ALBERT

Description: Dataset: BLOOFINZ-GoM flow cytometry abundance

Description: Phytoplankton and bacteria abundance from flow cytometry from samples collected in the Gulf of Mexico on R/V Nancy Foster cruises NF1704 and NF1802 in May 2017 and May 2018 For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/835414

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1851558, National Oceanic and Atmospheric Administration (NOAA) NA16NMF4320058

Description: Dataset: Coral Associated Microbes on Mo'orean Coral Reefs

Description: Three species of coral, plus water and sediment, were sampled at 21 sites around the island of Mo’orea, French Polynesia during the dry and rainy seasons in 2017 and 2018. Coral associated microbes (bacteria and archaea) were investigated and their community composition characterized through sequencing of the 16S rRNA gene. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/845039

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1635798, NSF Division of Ocean Sciences (NSF OCE) OCE-1635913

Description: Dataset: CTD Profile Casts

Description: CTD Depth Profile Cast Data for the InVirT-2019-BATS (Bermuda Atlantic Time Series) project taken in the on board of the R/V Atlantic Explorer AE1926 in 2019. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/835593

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1829636

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gosselin, K. M., Nelson, R. K., Spivak, A. C., Sylva, S. P., Van Mooy, B. A. S., Aeppli, C., Sharpless, C. M., O’Neil, G. W., Arrington, E. C., Reddy, C. M., & Valentine, D. L. Production of two highly abundant 2-methyl-branched fatty acids by blooms of the globally significant marine cyanobacteria Trichodesmium erythraeum. ACS Omega, 6(35), (2021): 22803–22810, https://doi.org/10.1021/acsomega.1c03196.

Description: The bloom-forming cyanobacteria Trichodesmium contribute up to 30% to the total fixed nitrogen in the global oceans and thereby drive substantial productivity. On an expedition in the Gulf of Mexico, we observed and sampled surface slicks, some of which included dense blooms of Trichodesmium erythraeum. These bloom samples contained abundant and atypical free fatty acids, identified here as 2-methyldecanoic acid and 2-methyldodecanoic acid. The high abundance and unusual branching pattern of these compounds suggest that they may play a specific role in this globally important organism.

Description: This work was funded with grants from the National Science Foundation grants OCE-1333148, OCE-1333162, and OCE-1756254 and the Woods Hole Oceanographic Institution (IR&D). GCxGC analysis made possible by WHOI’s Investment in Science Fund.

Description: Dataset: MO - biogeochemical and microbial field surveys

Description: Biogeochemical and microbial field surveys from the BATS site, Bermuda from R/V Atlantic Explorer cruises from 2009-2013. This dataset includes water samples collected from 2009-2013 at the Bermuda Hydrostation that were analyzed for DOC, POC, bacterial abundance, leucine, and thymidine incorporation. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/543314

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-0802004

Description: Dataset: Diatom Matrix RNAseq

Description: Transcriptome data for bacteria Ruegeria pomeroyi DSS-3, Stenotrophomonas sp. SKA14, Polaribacter dokdonensis MED152, and Dokdonia MED134 collected eight hours after individual inoculation into a diatom Thalassiosira psuedonana culture. The sequence data description for PRHNA448168 is at https://www.ncbi.nlm.nih.gov/bioproject/?term=PRJNA448168. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/818765

Description: NSF Division of Integrative Organismal Systems (NSF IOS) IOS-1656311

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Oceanographic Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2019.

Description: Marine microbes are key drivers of biogeochemical transformations within the world’s oceans. Although seawater appears uniform at scales that humans often interact with and sample, the world that marine microbes inhabit can be highly heterogeneous, with numerous biological and physical processes giving rise to resource hotspots where nutrient concentrations exceed background levels by orders of magnitude. While the impact of this microscale heterogeneity has been investigated in the laboratory with microbial isolates and theoretical models, microbial ecologists have lacked adequate tools to interrogate microscale processes directly in the natural environment. Within this thesis I introduce three new technologies that enable interrogation of microbial processes at the microscale in natural marine communities. The IFCB-Sorter acquires images and sorts individual phytoplankton cells, directly from seawater, allowing studies exploring connections between the diversity of forms present in the plankton and genetic variability at the single-cell level. The In Situ Chemotaxis Assay (ISCA) is a field-going microfluidic device designed to probe the distribution and role of motility behavior among microbes in aquatic environments. By creating microscale hotspots that simulate naturally occurring ones, the ISCA makes it possible to examine the role of microbial chemotaxis in resource acquisition, phytoplankton-bacteria interactions, and host-symbiont systems. Finally, the Millifluidic In Situ Enrichment (MISE) is an instrument that enables the study of rapid shifts in gene expression that permit microbial communities to exploit chemical hotspots in the ocean. The MISE subjects natural microbial communities to a chemical amendment and preserves their RNA in a minute-scale time series. Leveraging an array of milliliter-volume wells, the MISE allows comparison of community gene expression in response to a chemical stimulus to that of a control, enabling elucidation of the strategies employed by marine microbes to survive and thrive in fluctuating environments. Together, this suite of instruments enables culture-independent examination of microbial life at the microscale and will empower microbial ecologists to develop a more holistic understanding of how interactions at the scale of individual microbes impact processes in marine ecosystems at a global scale.

Description: I’d like to thank the Gordon and Betty Moore Foundation, the National Science Foundation, and NSERC for funding portions of my research.

Description: I’d like to thank the Gordon and Betty Moore Foundation, the National Science Foundation, and NSERC for funding portions of my research.

Description: Dataset: qPCR

Description: These data include the quantification of specific microbial taxa within the sediments collected during Integrated Ocean Drilling Program (IODP) Expedition 347: Baltic Sea. DNA was extracted from the interior of frozen whole round cores sampled from Little Belt, Anholt Loch, Landsort Deep, and Bornholm Basin at The University of Tennessee. For a more detailed description of drill sites, access the data set, "IODP-347 drill site locations". Primers specifically targeting the 16S rRNA gene of bacteria, archaea, anaerobic methane oxidizers (ANME-1), and Miscellaneous Crenarchaeota Group (MCG; taxonomically reassigned as the Bathyarchaeota phylum of Archaea) were used to assess abundance of these microbial groups. Abundance data was generated using quantitative-PCR (qPCR) and a non-specific, intercalating DNA stain, SYBR Green. Values were compared against a standard curve to generate copies/uL. These data were collected by Alex Shumaker as part of Dr. Karen Lloyd and Dr. Andrew Steen’s project funded by the National Science Foundation entitled, "Quantifying the contribution of the deep biosphere in the marine sediment carbon cycle using deep-sea sediment cores from the Baltic Sea". For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/641358

Description: NSF Division of Ocean Sciences (NSF OCE) OCE-1431598

Description: Dataset: Inferno vent plume proteins-Av1

Description: Proteins identified from the black smoker chimney Inferno hydrothermal vent plume waters at Axial Seamount, an active volcano along the Juan de Fuca Ridge spreading center, were identified using tandem mass spectrometry (MS/MS). These data are reported as Supplementary Table 3 and discussed in the on-line publication “Sulfur oxidizers dominate carbon fixation at a biogeochemical hot spot in the dark ocean” by Mattes, et al., 2013. doi for that publication: 10.1038/ismej.2013.113. This is the first of two replicate datasets. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/627835

Description: NSF Ocean Sciences (NSF OCE) OCE-1232840

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2015

Description: The spatial and temporal evolution of stratified shear instabilities is quantified in a highly stratified and energetic estuary. The measurements are made using high-resolution acoustic backscatter from an array composed of six calibrated broadband transducers connected to a six-channel high-frequency (120-600 kHz) broadband acoustic backscatter system. The array was mounted on the bottom of the estuary and looking upward. The spatial and temporal evolution of the waves is described in terms of their wavelength, amplitude and turbulent dissipation as a function of space and time. The observed waves reach an arrested growth stage nearly 10 times faster than laboratory and numerical experiments performed at much lower Reynolds number. High turbulent dissipation rates are observed within the braid regions of the waves, consistent with the rapid transition to arrested growth. Further, it appears that the waves do not undergo periodic doubling and do not collapse once their maximum amplitude is reached. Under some conditions long internal waves may provide the perturbation that decreases the gradient Richardson number so as to initiate shear instability. The initial Richardson number for the observed instabilities is likely between 0.1 and 0.2 based on the slope and growth rate of the shear instabilities.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2014

Description: Motivated by inspection of complex underwater environments, we have developed a system for multi-sensor SLAM utilizing both structured and unstructured environmental features. We present a system for deriving planar constraints from sonar data, and jointly optimizing the vehicle and plane positions as nodes in a factor graph. We also present a system for outlier rejection and smoothing of 3D sonar data, and for generating loop closure constraints based on the alignment of smoothed submaps. Our factor graph SLAM backend combines loop closure constraints from sonar data with detections of visual fiducial markers from camera imagery, and produces an online estimate of the full vehicle trajectory and landmark positions. We evaluate our technique on an inspection of a decomissioned aircraft carrier, as well as synthetic data and controlled indoor experiments, demonstrating improved trajectory estimates and reduced reprojection error in the final 3D map.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2014

Description: Underwater acoustic communication is an extremely complex field that faces many challenges due to the time-varying nature of the ocean environment. Vector sensors are a proven technology that when utilizing their directional sensing capabilities allows us to minimize the effect of interfering noise sources. A traditional pressure sensor array has been the standard for years but suffers at degraded signal to noise ratios (SNR) and requires maneuvers or a lengthly array aperture to direction find. This thesis explores the effect of utilizing a vector sensor array to steer to the direction of signal arrival and the effect it has on equalization of the signal at degraded SNRs. It was demonstrated that utilizing a single vector sensor we were able steer to the direction of arrival and improve the ability of an equalizer to determine the transmitted signal. This improvement was most prominent when the SNR was degraded to levels of 0 and 10 dB where the performance of the vector sensor outperformed that of the pressure sensor in nearly 100% of cases. Finally, this performance improvement occured with a savings in computational expense.

Description: ONR Grants #N00014-11-10426 and #N00014-07-10738

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2014

Description: Viral predation on bacteria in the ocean liberates carbon from the particulate fraction, where it is accessible to higher trophic levels, and redirects it to the dissolved fraction, where it supports microbial growth. Although viruses are highly abundant in the ocean little is known about how their interactions with bacteria are structured. This challenge arises because the diversity of both bacteria and viruses is exceedingly high and interactions between them are mediated by specific molecular interactions. This thesis uses heterotrophic bacteria of the genus Vibrio as a model to quantify virus-host interactions in light of host population structure and ecology. The methods developed in this thesis include streamlining of standard bacteriophage protocols, such as the agar overlay, and facilitate higher throughput in the isolation and characterization of novel environmental virus-host systems. Here, 〉1300 newly isolated Vibrio are assayed for infection by viral predators and susceptibility is found to be common, though total concentrations of predators are highly skewed, with most present at low abundance. The largest phylogenetically-resolved host range cross test available to date is conducted, using 260 viruses and 277 bacterial strains, and highly-specific viruses are found to be prevalent, with nearly half infecting only a single host in the panel. Observations of blocks of multiple viruses with nearly identical infection profiles infecting sets of highly-similar hosts suggest that increases in abundance of particular lineages of bacteria may be important in supporting the replication of highly specific viruses. The identification of highly similar virus genomes deriving from different sampling time points also suggests that interactions for some groups of viruses and hosts may be stable and persisting. Genome sequencing reveals that members of the largest broad host-range viral group recovered in the collection have sequence homology to non-tailed viruses, which have been shown to be dominant in the surface oceans but are underrepresented in culture collections. By integrating host population structure with sequencing of over 250 viral genomes it is found that viral groups are genomically cohesive and that closely-related and co-occurring populations of bacteria are subject to distinct regimes of viral predation.

Description: I also gratefully acknowledge the WHOI Ocean Ventures Fund, which provided funding for the sequencing of over 250 viral genomes of the Nahant Collection and thereby contributed immensely to the impact of the thesis work presented here. Work presented in this thesis was also made possible by support from National Science Foundation grant DEB 0821391, National Institute of Environmental Health Sciences grant P30- ES002109, the Moore Foundation and the Broad Institute’s SPARC program.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1993

Description: There is a growing consensus that the sound generated by breaking waves is responsible for much of the ambient noise level in the ocean. While numerous field measurements have shown a strong correlation between the ambient noise spectrum level (N) in the range 100Hz to 25kHz and wind speed in the ocean, very little has been done to establish a comparable correlation between the ambient noise spectrum level and surface wave field parameters. The difficulty in establishing this relationship is remarkable given that the frequency and intensity of wave breaking are dependent on the characteristics of the wave field. In Fall 1991, an experiment was conducted from the research platform Flip 130 kilometers off the coast of Oregon, where the ambient noise between 2.5 and 25 kHz, the wind speed, and the sea surface elevation using wire wave gauges were measured. The correlation between N and the root mean square wave amplitude a was found to be poor but could be improved if the swell was filtered out from the wave elevation time series. The influence of swell on the value of a was disproportionate to the level of ambient noise since its characteristics were not directly due to the local wind-wave conditions. Observations of the dependence of the high frequency wind waves and the directional wave spectrum under turning winds suggested that the high frequency wave components responded more quickly to changes in the wind speed and wind direction than the energy-containing frequencies. The ambient noise level also correlated well with the root mean square wave slopes. This is consistent with previous laboratory measurements which showed that the steepness of a packet of waves correlates with the strength of wave breaking and with characteristics of breaking waves such as loss of momentum flux, dissipation, initial volume of air entrained, mixing, and sound generation. Comparisons of surface wave dissipation estimates using field measurements and models developed by Phillips (1985) and Hasselmann (1974) show that although the two models have very different forms, they give values that are comparable in magnitude. The relationship between the ambient noise level and log of dissipation give correlation coefficients (0.93-0.95) that are comparable to those between ambient noise and wind speed. The mean square acoustic pressure was shown to vary with the dissipation, with p2 ∝ D0.6-0.8. The results suggest that measurements of ambient sound may prove to be useful in inferring surface wave dissipation.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1997

Description: Acoustic propagation in the ocean inevitably encounters inhomogeneities of various types, which give rise to scattering. Acoustic scattering from rough water /bottom interfaces comprised of exposed rocks and sea mountains gives way to volumetric scattering in areas with fiat interfaces and thick sediment cover. The data analysis of the ARSRP backscattering experiment revealed that random inhomogeneities in two irregular layers beneath the seafloor were the primary contributors to oblique backscattering in a sediment pond on the western flank of the Mid-Atlantic Ridge. In this thesis, an attempt has been made to model monostatic backscattering from 3-D volume inhomogeneities in the sediment and to compare the results with the ARSRP backscattering data. A scattering process cannot be modeled correctly without a proper account of the incident field . Several approximate propagation models have been evaluated against the exact solution, while the appropriateness of using the equivalent surface scattering strength in volume scattering characterizations is studied. This study concludes that precautions need to be taken in modeling both the propagation effects and the scattering mechanisms associated with the bottom volume scattering process. A volume scattering model based on perturbation theory and the Born approximation is developed incorporating contributions from both sound speed and density fluctuations. With the propagation part handled accurately by OASES and random fluctuations generated effectively by a new scheme modified from the spectral method, the model is capable of simulating the monostatic backscattered field and time series due to 3-D volumetric sediment inhomogeneities. Both the characteristic length scale and power spectrum descriptions of the random inhomogeneities are shown to have great impact on the backscattered field by parameter studies in a free-space scenario. The important roles played by horizontal anisotropy and the vertical correlation of the random field have been demonstrated. Density fluctuations are further confirmed to be the dominant force in backscattering. The model matches the ARSRP backscattering data very well, with the fluctuations of sound speed and density in the two irregular layers described by a power law type of power spectrum.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1997

Description: This work is concerned with coherent communication by means of acoustic signals over underwater communication channels. The estimated scattering functions of real data ranging from the Arctic environment to tropical waters show that underwater communication channels can not be captured by a single, simple channel model. This thesis considers mainly a subset of underwater communication channels where the Doppler spread is more severe than the delay spread. An appropriate representation of the linear time- variant channel is introduced, and the wide sense stationary uncorrelated scattering (WSSUS) channel assumption enables characterization in terms of scattering functions. The concept of Doppler lines, which are frequency domain filters, is used in the derivation of a receiver for Doppler spread channels. The channel is simulated by means of a ray representation for the acoustic field and a time-variant FIR filter. The impact of physical ocean processes on the Doppler spread is demonstrated, and from this modeling explanations for the Doppler spread observed in real data are obtained. A decision feedback equalizer (DFE) adapted with recursive least squares (RLS) is analyzed, and its limit with respect to pure Doppler spread is found. By using the DFE with a phase locked loop (PLL) suboptimal system behavior is found, and this is verified on real data. In the case of a simple Doppler shift the cross-ambiguity function is used to estimate the shift, and the received signal is phase rotated to compensate this before it enters the receiver. A modified RLS called the time updated RLS (TU-RLS) is presented, and it is used in a new receiver. This receiver is initialized by means of the cross-ambiguity function and the performance is characterized by probability of decoding error vs delay spread, Doppler spread and SNR. The receiver uses Doppler lines to compensate both discrete and continuous Doppler spread. The receiver stability depends on the conditioning of the block diagonal correlation matrix propagated by the TU-RLS. The receiver is used to decode both real and simulated data, and some of these data are severely Doppler spread.

Description: The work in this thesis was funded in part by the Norwegian Research Counsil under a general PhD contract, the education office of Woods Hole Oceanographic Institution and the Office of Naval Research under contracts N00014-95-0153 and N00014-95-l-0322.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1997

Description: As part of the Shallow Water Acoustics in a Random Medium (SWARM) experiment [1], a sixteen element WHOI vertical line array (WVLA) was moored in 70 meters of water off the New Jersey coast. This array was sampled at 1395 Hz or higher for the seven days it was deployed. Tomography sources with carrier frequencies of 224 and 400 Hz were moored about 32 km shoreward, such that the acoustic path was anti-parallel to the primary propagation direction for shelf generated internal wave solitons. Two models for the propagation of normal modes through a 2-D waveguide with solitary internal wave (soliton) scattering included are developed to help in understanding the very complicated mode arrivals seen at the WVLA. The simplest model uses the Preisig and Duda [2] sharp interface approximation for solitons, allowing for rapid analysis of the effects of various numbers of solitons on mode arrival statistics. The second model, using SWARM thermistor string data to simulate the actual SWARM waveguides, is more realistic, but much slower. The analysis of the actual WVLA data yields spread, bias, wander, and intensity fluctuation signals that are modulated at tidal frequencies. The signals are consistent with predicted relationships to the internal wave distributions in the waveguides.

Description: The funds for my education were provided by the Office of Naval Research through an ONR Fellowship (MIT award 002734-001); the funds for SWARM were also provided by the Office of Naval Research through ONR Grant N00014-95-0051.

Description: This is the first volume of an international scientific journal that is dedicated to issues of geoethics and geological culture. Its goal is to inform the Italian and international scientific communities about what emerged at the GeoItalia 2011 conference, attended by not only Italian geoscientists. At this conference, the geoscientists questioned their role in society and the responsibilities that they have to assume as scholars of the planet Earth and experts of the territory. They highlighted the need for rediscovery of the cultural values of geology as a science that can contribute to the construction of correct social knowledge, and the need to be aware that geoethics cannot exist without a real awareness among geoscientists of the cultural value of the Earth sciences.

Description: Published

Description: 331

Description: 5.9. Formazione e informazione

Description: JCR Journal

Description: open

Description: Prof. Giulio Giorello is amongst the most prominent philosophers of science in Italy and in the world. He is currently Professor of the Philosophy of Science at the University of Milan, Director of the Series ‘Science and Ideas’ (Raffaele Cortina Books Editor), and Literary Journalist of the cultural pages of the Corriere della Sera, one of the most important of the Italian newspapers. In this keynote presentation, in interview form, he talks about the value that the Earth sciences have had through history, framing this group of disciplines in ethical and epistemological terms, and highlighting some important elements that have to be considered in geological activities.

Description: Published

Description: 343-346

Description: 5.9. Formazione e informazione

Description: JCR Journal

Description: open

Description: The international debate in the field of geoethics focuses on some of the most important environmental emergencies, while highlighting the great responsibilities of geoscientists, whatever field they work in, and the important social, cultural and economic repercussions that their choices can have on society. The GeoItalia 2009 and 2011 conferences that were held in Rimini and Turin, respectively, and were organized by the Italian Federation of Earth Science, were two important moments for the promotion of geoethics in Italy. They were devoted to the highlighting of how, and with what tools and contents, can the geosciences contribute to the cultural renewal of society. They also covered the active roles of geoscientists in the dissemination of scientific information, contributing in this way to the correct construction of social knowledge. Geology is culture, and as such it can help to dispel misconceptions and cultural stereotypes that concern natural phenomena, disasters, resources, and land management. Geological culture consists of methods, goals, values, history, ways of thinking about nature, and specific sensitivity for approaching problems and their solutions. So geology has to fix referenced values, as indispensable prerequisites for geoethics. Together, geological culture and geoethics can strengthen the bond that joins people to their territory, and can help to find solutions and answers to some important challenges in the coming years regarding natural risks, resources, and climate change. Starting from these considerations, we stress the importance of establishing an ethical criterion for Earth scientists, to focus attention on the issue of the responsibility of geoscientists, and the need to more clearly define their scientific identity and the value of their specificities.

Description: Published

Description: 335-341

Description: 5.9. Formazione e informazione

Description: JCR Journal

Description: open

Description: Franco Ferrarotti, Professor emeritus at ‘La Sapienza’ University of Rome; since winning the first Chair in this discipline in Italy in 1961, he has been considered the Father of Italian Sociology. An independent Member of Italian Parliament in the third government (1958-1963), a member of the New York Academy of Sciences, and a ‘visiting Professor’ at many universities in Europe, North America, Russia, Japan and Latin America. Franco Ferrarotti has taught and still teaches in Europe and America, and he has received many awards throughout his career. In this interview, he talks about the social aspects and consequences of Earth sciences studies.

Description: Published

Description: 347-348

Description: 5.9. Formazione e informazione

Description: JCR Journal

Description: open

Description: We argue here that the introduction of an ethical code of conduct that follows the example of the Hippocratic Oath of physicians will help geologists to acquire binding awareness of their professional and social responsibilities. The ethical behavior and obligations of modern geologists involve, but are not limited to, the following issues: correct land/ environment use and management; respect of truth and science; and protection of the Earth systems, on both the local and global scales, and therefore, of our well-being. We believe that for geoligists, the explicit acceptance of an ethical code will help to promote: (i) an awareness of their social role, expertise and sense of belonging to a professional community; (ii) an understanding of the expectations of citizens and society; and (iii) cultural growth, with better use of research and implementation of scientific and professional skills. All this should enhance the public recognition of the social mission of geologists, which is essential for the well-being of society. Therefore, we suggest that like in the majority of medical schools, ethical training should be a part of the university curriculum for students in geology.

Description: Published

Description: 365-369

Description: 5.9. Formazione e informazione

Description: JCR Journal

Description: open

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2012

Description: Adaptive equalization is an important aspect of communication systems in various environments. It is particularly important in underwater acoustic communication systems, as the channel has a long delay spread and is subject to the effects of time- varying multipath fading and Doppler spreading. The design of the adaptation algorithm has a profound influence on the performance of the system. In this thesis, we explore this aspect of the system. The emphasis of the work presented is on applying concepts from inference and decision theory and information theory to provide an approach to deriving and analyzing adaptation algorithms. Limited work has been done so far on rigorously devising adaptation algorithms to suit a particular situation, and the aim of this thesis is to concretize such efforts and possibly to provide a mathematical basis for expanding it to other applications. We derive an algorithm for the adaptation of the coefficients of an equalizer when the receiver has limited or no information about the transmitted symbols, which we term the Soft-Decision Directed Recursive Least Squares algorithm. We will demonstrate connections between the Expectation-Maximization (EM) algorithm and the Recursive Least Squares algorithm, and show how to derive a computationally efficient, purely recursive algorithm from the optimal EM algorithm. Then, we use our understanding of Markov processes to analyze the performance of the RLS algorithm in hard-decision directed mode, as well as of the Soft-Decision Directed RLS algorithm. We demonstrate scenarios in which the adaptation procedures fail catastrophically, and discuss why this happens. The lessons from the analysis guide us on the choice of models for the adaptation procedure. We then demonstrate how to use the algorithm derived in a practical system for underwater communication using turbo equalization. As the algorithm naturally incorporates soft information into the adaptation process, it becomes easy to fit it into a turbo equalization framework. We thus provide an instance of how to use the information of a turbo equalizer in an adaptation procedure, which has not been very well explored in the past. Experimental data is used to prove the value of the algorithm in a practical context.

Description: Support from the agencies that funded this research- the Academic Programs Office at WHOI and the Office of Naval Research (through ONR Grant #N00014-07-10738 and #N00014-10-10259).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1998

Description: Work on the forward problem in zooplankton bioacoustics has resulted in the identification of three categories of acoustic scatterers: elastic-shelled (e.g. pteropods), fluid-like (e.g. euphausiids), and gas-bearing (e.g. siphonophores). The relationship between backscattered energy and animal biomass has been shown to vary by a factor of —19,000 across these categories, so that to make accurate estimates of zooplankton biomass from acoustic backscatter measurements of the ocean, the acoustic characteristics of the species of interest must be well-understood. This thesis describes the development of both feature based and model based classification techniques to invert broadband acoustic echoes from individual zooplankton for scatterer type, as well as for particular parameters such as animal orientation. The feature based Empirical Orthogonal Function Classifier (EOFC) discriminates scatterer types by identifying characteristic modes of variability in the echo spectra, exploiting only the inherent characteristic structure of the acoustic signatures. The model based Model Parameterisation Classifier (MPC) classifies based on correlation of observed echo spectra with simplified parameterisations of theoretical scattering models for the three classes. The Covariance Mean Variance Classifiers (CMVC) are a set of advanced model based techniques which exploit the full complexity of the theoretical models by searching the entire physical model parameter space without employing simplifying parameterisations. Three different CMVC algorithms were developed: the Integrated Score Classifier (ISC), the Pairwise Score Classifier (PSC) and the Bayesian Probability Classifier (BPC); these classifiers assign observations to a class based on similarities in covariance, mean, and variance, while accounting for model ambiguity and validity. These feature based and model based inversion techniques were successfully applied to several thousand echoes acquired from broadband (-350 kHz - 750 kHz) insonifications of live zooplankton collected on Georges Bank and the Gulf of Maine to determine scatterer class. CMVC techniques were also applied to echoes from fluid-like zooplankton (Antarctic krill) to invert for angle of orientation using generic and animal-specific theoretical and empirical models. Application of these inversion techniques in situ will allow correct apportionment of backscattered energy to animal biomass, significantly improving estimates of zooplankton biomass based on acoustic surveys.

Description: Thanks to the WHOI/MIT Joint Program Education Office for partial funding. Other sources of funding for my thesis work include the Ocean Acoustics, Oceanic Biology and URIP programs of the Office of Naval Research grant numbers N00014-89- J-1729, N00014-95-1-0287 and N00014-924-1527, and the Biological Oceanography program of the National Science Foundation grant number OCE-9201264.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990

Description: Travel-times of acoustic signals were measured between a bottom-mounted source near Oahu and four bottom-mounted receivers located near Washington, Oregon, and California in 1988 and 1989. This paper discusses the observed tidal signals. At three out of four receivers, observed travel times at M2 and S2 periods agree with predictions from barotropic tide models to within ±30° in phase and a factor of 1.6 in amplitude. The discrepancy at the fourth receiver can be removed by including predicted effects of phase-locked baroclinic tides generated by seamounts. Our estimates of barotropic M2 tidal dissipation by seamounts vary between 2 x 1016 and 1 X 1018 erg·s-1. The variation by two orders of magnitude is due to uncertainties in the numbers and sizes of seamounts. The larger dissipation (1 x 1018 erg·s-1) is the same order as previous estimates and amounts to 4% of the total dissipation at M2.

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution January 1994

Description: In 1991 the Heard Island Feasibility Test demonstrated that it is possible to transmit coded acoustic signals nearly half way around the world. One of the key issues in the feasibility test was to determine the spatial structure of the received transmissions. In this thesis, data from the Canadian Defense Research Establishment Pacific horizontal line array is used to form an estimate of the directional power spectrum. This spectrum determines if any horizontal multipath is detectable. The preliminary signal conditioning, including frequency spectrum estimation and demodulation required before beamforming is described. Conventional and adaptive beamforming methods are examined with synthetic data to demonstrate the limitations on the directional spectrum results. The principle result of this work is that no stable horizontal multipath is evident. The mean arrival angle for the five hours of data analyzed is 212° ± 1.5°.

Description: The Office of Naval Research provided funding for the author under the ONR fellowship program.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1989

Description: The problem of a low-frequency acoustic plane wave incident upon a free surface coupled to a semi-infinite elastic plate surface, is solved using an analytic approach based on the Wiener-Hopf method. By low-frequency it is meant that the elastic properties of the plate are adequately described by the thin plate equation (kH ≲ 1). The diffraction problem relates to issues in long range sound propagation through partially ice-covered Arctic waters, where open leads or polynya on the surface represent features from which acoustic energy can be diffracted or scattered. This work focusses on ice as the material for the elastic plate surface, and, though the solution methods presented here have applicability to general edge diffraction problems, the results and conclusions are directed toward the ice lead diffraction process. The work begins with the derivation of an exact solution to a canonical problem: a plane wave incident upon a free surface (Dirichlet boundary condition) coupled to a perfectly rigid surface (Neumann boundary condition). Important features of the general edge diffraction problem are included here, with the solution serving as a guideline to the more complicated solutions presented later involving material properties of the boundary. The ice material properties are first addressed using the locally reacting approximation for the input impedance of an ice plate, wherein the effects of elasticity are ignored. This is followed by use of the thin plate equation to describe the input impedance, which incorporates elements of elastic wave propagation. An important issue in working with the thin plate equation is the fluid loading pertaining to sea ice and low-frequency acoustics, which cannot be characterized by simplifying heavy or light fluid loading limits. An approximation to the exact kernel of the Wiener-Hopf functional equation is used here, which is valid in this mid-range fluid loading regime. Use of this approximate kernel allows one to proceed to a complete and readily interpretable solution for the far field diffracted pressure, which includes a subsonic flexural wave in the ice plate. By using Green's theorem, in conjunction with the behavior of the diffracted field along the two-part planar boundary, the functional dependence of ∏D (total diffracted power) in terms of k (wavenumber), H (ice thickness), α (grazing angle) and the combined elastic properties of the ice sheet and ambient medium, is determined. A means to convert ∏D into an estimate of dB loss per bounce is developed using ray theoretical methods, in order to demonstrate a mechanism for acoustic propagation loss attributed directly to ice lead diffraction effects. Data from the 1984 MIZEX (Marginal Ice Zone Experiments) narrow-band acoustic transmission experiments are presented and discussed in this context.

Description: I also gratefully acknowledge financial support provided by the WHOI Education Office and the Office of Naval Research.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1989

Description: Variability of the Florida Current has been monitored via acoustic tomography. A reciprocal tomography experiment was conducted in the eastern half of the Florida Straits during mid October and November, 1983. A triangular array of transceivers, with leg separations of approximately 45 kilometers, was deployed at 27°N. The presence of a surface mixed layer in the region allowed for the ducted propagation of acoustic energy in the surface layer. A deeper layer was sampled by an unresolved group of refracted, bottom reflected ray arrivals. Incorporating the complete set of arrivals, we are able to obtain depth dependent estimates of the temperature field, current velocity, and relative vorticity. The oceanography of the region has been shown to be dominated by the lateral shifting of the surface and subsurface core of the Florida Current. The influx of westward flowing water through the Northwest Providence Channel at 26°N also appears as a large scale signal in the eastern Florida Straits. Low frequency fluctuations of temperature, current velocity, and vorticity occur at periods ranging from several days to nearly two weeks, and are intimately related to meandering of the Florida Current system.

Description: This research was carried out under ONR contract N00014-86-K-0751.

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990

Description: The propagation of low frequency seismo-acoustic waves in the Arctic Ocean ice canopy is examined through the analysis of hydrophone and geophone data sets collected in 1987 at an ice camp designated PRUDEX in the Beaufort Sea. Study of the geophone time series generated by under-ice explosive detonations reveals not only the expected longitudinal and flexural waves in the ice plate, but also an unexpected horizontally-polarized transverse (SH) wave arriving at a higher amplitude than the other wave types. The travel paths of all three observed wave types are found to be refracted in the horizontal plane along a line coincident with a known ridge separating the ice canopy locally into two distinct half-plates, the first of thin first year ice and the second of thicker multi-year ice. The origin of the SH wave appears to be near the detonation and not associated with the interaction of longitudinal, flexural or waterborne waves with the ridge line. The need to determine the exact location of each detonation from the received time series highlights the dramatic superiority of geophones over hydrophones in this application, as does the ability to detect the anomalous SH waves and the refracted ray paths, neither of which are visible in the hydrophone data. Inversion of the geophone data sets for the low frequency elastic parameters of the ice is conducted initially by treating the ice as a single homogeneous isotropic plate to demonstrate the power of SAFARI numerical modeling in this application. A modified stationary phase approach is then used to extend SAFARI modeling to invert the data sets for the elastic parameters of the two ice half-plates simultaneously. The compressional/shear bulk wave speeds estimated in the half-plates, 3500/1750 m/s in the multi-year ice and 3000/1590 m/ s in the new ice, are comparable to previously obtained values; however, the compressional/shear attenuation values in the two half-plates, 1.0/2.99 d/Bλ. and 1.0/2.67 dB/λ, respectively, are somewhat greater than previously measured values and four times greater than estimates extrapolated from high frequency data.

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990

Description: Pulse-like acoustic signals are transmitted from an acoustic source near Oahu to seven receivers off the west coast of the United States for a 124-day period in 1988. Acoustic travel-time oscillations are observed in the received signal at periods between 15 and 23 hours, which are caused by barotropic (or first or second mode baroclinic) flu ctuations in the ocean. It is shown that these fluctuations cannot be local processes isolated to either the source or to the receivers. It is further shown that resonant barotropic gravity wave modes (Platzman et al., 1981) are not consistent with the data. The cause of these flu ctuations remains unresolved, but the data and other oceanographic measurements put many constraints on the process causing these fluctuations.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1996

Description: The shallow water acoustic channel supports far-field propagation in a discrete set of modes. Ocean experiments have confirmed the modal nature of acoustic propagation, but no experiment has successfully excited only one of the suite of mid-frequency propagating modes propagating in a coastal environment. The ability to excite a single mode would be a powerful tool for investigating shallow water ocean processes. A feedback control algorithm incorporating elements of adaptive estimation, underwater acoustics, array processing and control theory to generate a high-fidelity single mode is presented. This approach also yields a cohesive framework for evaluating the feasibility of generating a single mode with given array geometries, noise characteristics and source power limitations. Simulations and laboratory waveguide experiments indicate the proposed algorithm holds promise for ocean experiments.

Description: Josko Catipovic funded my research for summer of 1992 on the Office of Naval Research Grant Number N00014-92-J-1661 and from June 1993 through August 1995 on Defense Advanced Research Projects Agency Grant Number MDA972-92-J- 1041. The Office of Naval Research Grant N00014-95-1-0362 to MIT supported the computer facilities used to do much of this work.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1998

Description: The goal of this thesis is to develop a methodology to interpret sound scattered from the seafloor in terms of seafloor structure and subseafloor geological properties. Specifically, this work has been directed towards the interpretation of matched-filtered, beamformed monostatic acoustic reverberation data acquired on the west flank of the Mid-Atlantic Ridge when the seafloor is insonified by a band-limited, low-grazing-angle acoustic pulse. This research is based on the hypothesis that observed backscatter signals are produced by a combination of seafloor (interface) scattering and subseafloor (volume) scattering from structure having variations at scale lengths similar to the wavelength of the insonifying acoustic field. Analysis of monostatic reverberation data acquired during the Site A experiment (Run 1) of the Acoustic Reverberation Special Research Program 1993 Acoustics Cruise suggests that the scattered signals cannot be accounted for quantitatively in terms of large-scale slope, even though a strong correspondence between high intensity backscatter and seafloor ridges is observed. In order to investigate and quantify the actual sources of seafloor scattering, a numerical modeling study of seafloor models is undertaken using a finite-difference solution to the elastic wave equation. Geological data available at Site A and published reports describing geological properties of similar deep ocean crustal regions are used to develop a realistic seafloor model for the study area with realistic constraints on elastic parameters. Wavelength-scale heterogeneity in each model, in the form of seafloor roughness and subseafloor volume heterogeneity is defined using stochastic distributions with Gaussian autocorrelations. These distributions are quantified by their correlation lengths and standard deviation in amplitude. In order to incorporate all seafloor structure in a single parameterization of seafloor scattering, large-scale slope and wavelength-scale seafloor spatial parameters (rms height and correlation length), are included, along with the acoustic beam grazing-angle relative to a horizontal seafloor, in the definition of an 'effective grazing angle'. The Rayleigh roughness parameter, which depends on grazing angle of the insonification, is then redefined using the effective grazing angle and calculated for a variety of seafloor models. Scattering strengths are shown to vary systematically but nonlinearly with the 'effective Rayleigh roughness parameters' of horizontal rough seafloor models. This leads to an approximate interpretation scheme for backscatter intensity. In general, variation in backscattering is found to be dominated by the scattering from rough seafloor. If the seafloor is smooth or very low velocity (e.g., sediment), then scattering from volume heterogeneity becomes an important factor in the backscattered field. Both wavelength-scale seafloor roughness and volume heterogeneity are shown to be capable of producing the levels of variation in intensity observed in monostatic reverberation experiments. Variations in large-scale seafloor slope and subseafloor average velocity are shown to influence the backscatter response of seafloor models.

Description: My first year of study at MIT was supported by a Chevron Fellowship. The work in this thesis was funded by the Office of Naval Research under grant numbers N00014-93-1-1352, N00014-90-J-1493, and N00014-95-1-0506.

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1995

Description: The data analysis of a deep-sea bottom backscattering experiment, carried out over a sediment pond on the western flank of the Mid-Atlantic Ridge in July 1993 with a 250- 650 Hz chirp source and a vertical receiving array suspended near the fiat seafloor, is presented in this thesis. Reflected signals in the normal incidence direction as the output of endfire beamforming are used to determine the sediment structure. The sediment is found to be horizontally stratified, except for two irregular regions, each about 20 m t hick, located around 18 m and 60 m beneath the water-sediment interface. Multiple constraints beamforming is shown to be effective in removing coherent reflections from internal stratified layers, which is critical to the analysis of bottom backscattering. With backscattered signals obtained by beamforming, the above-mentioned two inhomogeneous regions are found to be the dominant factors on the bottom backscattered field, both in the normal incidence and oblique directions. The backscattering strength as a function of grazing angle is estimated for each of the two regions.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution March 1990

Description: This thesis introduces a new procedure for the enhancement of acoustic images of the bottom of the sea produced by side-scan sonars. Specifically, it addresses the problem of estimating and correcting geometric distortions frequently observed in such images as a consequence of motion instabilities of the sonar array. This procedure estimates the geometric distortions from the image itself, without requiring any navigational or attitude measurements. A mathematical model for the distortions is derived from the geometry of the problem, and is applied to estimates of the local degree of geometric distortion obtained by cross-correlating segments of adjacent lines of the image. The model parameters are then recursively estimated through deterministic least-squares estimation. An alternative approach based on adaptive Kalman filtering is also proposed, providing a natural framework in which a priori information about the array dynamics may be easily incorporated. The estimates of the parameters of the distortion model are used to rectify the image, and may also be used for estimating the attitude parameters of the array. A simulation is employed to evaluate the effectiveness of this technique and examples of its application to high-resolution side-scan sonar images are provided.

Description: This work was produced under sponsorship of the Conselho Nacional de Desenvolvimento Cient{jico e Tecnol6gico (CNPq), an agency of the Government of the Federative Republic of Brazil, and was supported in part by the Defense Advanced Research Projects Agency monitored by the Office of Naval Research under Grant No. N00014-89-J-1489, in part by the National Science Foundation under Grant No. MIP 87-14969, and in part by Sanders Associates, Incorporated.

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1991

Description: A model is developed for the prediction of the seismo-acoustic noise spectrum in the microseism peak region (0.1 to 0.7 Hz). The model uses a theory developed by Cato [J. Acoust. Soc. Am., 89 , 1096-1112 (1991)] for an infinite depth ocean in which the surface orbital motion caused by gravity waves may produce acoustic waves at twice the gravity wave frequency. Using directional wave spectra as inputs, acoustic source levels are computed and incorporated into a more realistic environment consisting of a horizontally stratified ocean with an elastic bottom. Noise predictions are made using directional wave spectra obtained from the SWADE surface buoys moored off the coast of Virginia and the SAFARI sound propagation code, with a bottom model derived using wave speeds measured in the EDGE deep seismic reflection survey. The predictions are analyzed for noise level variations with frequency, wave height, wind direction, and receiver depth. These predictions are compared to noise measurements made in ECONOMEX using near-bottom receivers located close to the surface buoys. Good agreement is found between the predictions and observations under a variety of environmental conditions.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1992

Description: An ultra-short baseline acoustic navigation system has been developed which is capable of determining bearing to a sound source with an error of less than 1° in typical operational conditions. The system has a demonstrated ability to operate in an environment in which multipath interference is significant. A DSP microprocessor is used to process signals received by two hydrophones from a 26 kHz toneburst sound source. This processing power is used to implement features not commonly available with commercial systems. The system has the capability to make an on-line measurement of the signal-tonoise ratio, which can be used to estimate the confidence which should be placed in the data. Estimates of phase difference and signal power are generated many times within each received pulse, so the effects of multi path interference throughout the pulse can be observed. Results of tests at several ranges are presented, and compared to performance models developed in the thesis. System performance is quantified, and an effort is made to understand the effects of multipath arrivals.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1993

Description: This thesis examines the use of a single, omnidirectional hydrophone as a receiving sensor to passively localize an acoustic beacon. The localization problem is presented as a constrained, nonlinear parameter estimation problem, and Lagrange multipliers are introduced to solve for the maximum likelihood estimate of the acoustic beacon's position. An iterative algorithm is developed using range difference measurements to solve for the maximum likelihood estimate of a stationary acoustic beacon's position. This algorithm is then _extended to include linear, constant velocity motion of the acoustic beacon. Finally, design specifications for a receiver to implement the maximum likelihood estimation algorithms are developed. To test the maximum likelihood estimate algorithms, Monte Carlo simulations are conducted. Results from six representative scenarios are presented. Test results show that as the number of range differences used increases, or the distance that the observer travels between received beacon signals increases, the accuracy of the estimated position improves. Also, tests show that accuracy of the estimated beacon position is directly related to the accuracy in which the observer's position is measured. To test the receiver's design specifications, a prototype receiver is built using commonly available components. It is then shown that the prototype receiver meets or exceeds the design specifications.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution February 1994

Description: This thesis presents the design and simulation of an acoustic listen-only navigation system for use in a time-varying high-multipath environment. The system uses a ray tracing model of sound propagation in a horizontally stratified ocean to associate each multipath arrival with a particular ray path through the ocean. This ray path identification allows an inversion for both vehicle position and sound speed profile parameters. Tracking changes in the sound speed profile allows the vehicle to maintain navigation accuracy in a time-varying acoustic environment. Simulation results for typical Arctic conditions indicate the potential for accurate navigation from acoustic beacons at ranges up to tens of kilometers.

Description: I also wish to acknowledge the support received from a National Science Foundation Graduate Fellowship under Grant #RCD-9154652 and from the Office of Naval Research Arctic Programs Office, which made possible this work.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution February 1994

Description: Ambient noise in the sea has been observed for over 100 years. Previous studies conclude that the primary source of microseisms is nonlinear interaction of surface gravity waves at the sea surface. Though this source relationship is generally accepted, the actual processes by which the wave generated acoustic noise in the water column couples and propagates to and along the sea floor are not well understood. In this thesis, the sources and propagation of sea floor and sub-sea floor microseismic noise between 0.2 and 10 Hz are investigated. This thesis involves a combination of theoretical, observational and numerical analysis to probe the nature of the microseismic field in the Blake Bahama Basin. Surface waves are the primary mechanism for noise propagation in the crust and fall into two separate groups depending on the relative wavelength/water depth ratio. Asymptotic analysis of the Sommerfeld integral in the complex ray parameter plane shows results that agree with previous findings by Strick (1959) and reveal two fundamental interface wave modes for short wavelength noise propagation in the crust: the Stoneley and pseudo-Rayleigh wave. For ocean sediments, where the shear wave velocity is less than the acoustic wave velocity of water, only the Stoneley interface wave can exist. For well consolidated sediments and basalt, the shear velocity exceeds the acoustic wave velocity of water and the pseudo-Rayleigh wave can also exist. Both interface waves propagate with retrograde elliptic motion at the sea floor and attenuate with depth into the crust, however the pseudo-Rayleigh wave travels along the interface with dispersion and attenuation and "leaks" energy into the water column for a half-space ocean over elastic crust model. For finite depth ocean models, the pseudo-Rayleigh wave is no longer leaky and approaches the Rayleigh wave velocity of the crust. The analysis shows that longer wavelength noise propagates as Rayleigh and Stoneley modes of the ocean+crust waveguide. These long wavelength modes are the fundamental mechanism for long range noise propagation. During the Low Frequency Acoustic Seismic Experiment (LFASE) a four-node, 12- channel borehole array (SEABASS) was deployed in the Blake Bahama Basin off the coast of eastern Florida (DSDP Hole 534B). This experiment is unique and is the first use of a borehole array to measure microseismic noise below the sea floor. Ambient background noise from a one week period is compared between an Ocean Bottom Seismometer (OBS) and SEABASS at sub-bottom depths of 10, 40, 70 and 100 meters below the sea floor. The 0.3 H z microseism peak is found to be nearly invariant with depth and has a power level of 65 and 75 dB rel 1 (nm/ s2)2)/ H z for the vertical and horizontal components respectively. At 100 m depth, the mean microseismic noise levels above 0.7 Hz are 10 dB and 15-20 dB quieter for the vertical and horizontal components respectively. Most of this attenuation occurs in the upper 10 m above 1.0 Hz, however higher modes in the spectra show narrow bandwidth variability in the noise field that is not monotonic with depth. Dispersion calculations show normal mode Stoneley waves below 0.7 Hz and evidence of higher modes above 0.8 Hz. A strong correlation between noise levels in the borehole and local sea state conditions is observed along with clear observation of the nonlinear frequency doubling effect between ocean surface waves and microseisms. Particle motion analysis further verifies that noise propagates through the array as Rayleigh/Stoneley waves. Polarization direction indicates at least two sources; distant westerly swell during quiescent times and local surface waves due to a passing storm. Above 1.0 Hz the LFASE data shows little coherence and displays random polarization. Because of this, we believe scattered energy is a significant component of the noise field in the Blake Bahama Basin. A fully 3-D finite difference algorithm is used to model both surface and volume heterogeneities in the ocean crust. Numerical modeling of wave propagation for hard and soft bottom environments shows that heterogeneities on the order of a seismic wavelength radiate energy into the water column and convert acoustic waves in the water into small wavelength Stoneley waves observed at the borehole. Sea floor roughness is the most important elastic scattering feature of the ocean crust. Comparisons of 2D and 3D rough sea floor models show that out-of-plane effects necessitate the use of 3D methods. The out-of-plane energy that is present in the LFASE data comes from either heterogeneities in the source field (i.e. mixed gravity wave directions) or, equally likely, scattering of the source field from surface or volume heterogeneities in the sea floor.

Description: This research was supported by Office of Naval Research grants N00014-89-C-0018, N00014-89-J-1012, N00014-90-C-0098, N00014-90-J-1493 and N00014-93-1-1352.

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990

Description: This paper develops a beam pattern design procedure for general multidimensional irregular sonar arrays that incorporates the not well understood effects of array geometry into the design process. The procedure is implemented by generating a "penalty function" in a spectral covariance function form. Processing the penalty function causes beam pattern high sidelobes to be penalized and the main lobe to be emphasized. This is accomplished by forming the penalty function in terms of an isotropic noise field of specified strength modified with a finite sector of low coherent energy and stabilized with incoherent sensor noise. By inputting the penalty function into a minimum variance beamformer, the beam pattern and aperture weights are calculated based on the given array geometry. The beamformer used is Capon's Maximum Likelihood Method. The array used to test the procedure is located on a sixty degree sector of a cylindrical surface. The procedure is implemented by two different methods, each with some desirable characteristics. One method suppresses sidelobes directly by the placement of nulls. The other method suppresses sidelobes indirectly by the enhancement of the main lobe with anti-nulls. Both methods are evaluated in terms of a sensitivity factor which constrains the maximum white noise array gain. Results show that both methods result in sidelobe levels that range from 20 to 35 dB lower compared to a conventional beam pattern with uniform aperture weighting and that the design procedure is applicable to beam patterns steered to both true broadside and to off-broadside directions.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2012

Description: Signal detection and synchronization in the time varying ocean environment is a difficult endeavor. The current common methods include using a linear frequency modulated chirped pulse or maximal length sequence as a detection pulse, then match filtering to that signal. In higher signal to noise ratio (SNR) environments (~0 dB and higher) this has been a suitable solution. As the SNR drops lower however, this solution no longer provides an acceptable probability of detection for a given tolerable probability of false alarm. The issue derives from the inherent coherence issues in the ocean environment which limit the useful matched filter length. This thesis proposes an alternative method of detection based on a recursive least squares linearly adaptive equalizer which we term the Adaptive Linear Equalizer Detector (ALED). This detectors performance has demonstrated reliable probability of detection with minimal interfering false alarms with SNR as low as -20 dB. Additionally this thesis puts forth a computationally feasible method for implementing the detector.

Description: Support from the Office of Naval Research (through ONR grant #N00014-07-10738 and #N00014-11-10426).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1999

Description: During July and August of 1996, a large acoustics/physical oceanography experiment was fielded in the Mid-Atlantic Bight, south of Nantucket Island, MA. Known as the Shelfbreak Front PRIMER Experiment, the study combined acoustic data from a moored array of sources and receivers with very high resolution physical oceanographic measurements. This thesis addresses two of the primary goals of the experiment, explaining the properties of acoustic propagation in the region, and tomographic inversion of the acoustic data. In addition, this thesis develops a new method for predicting acoustic coherence in such regions. Receptions from two 400 Hz tomography sources, transmitting from the continental slope onto the shelf, are analyzed. This data, along with forward propagation modeling utilizing SeaSoar thermohaline measurements, reveal that both the shelfbreak front and tidally-generated soliton packets produce stronger coupling between the acoustic waveguide modes than expected. Arrival time wander and signal spread show variability attributable to the presence of a shelf water meander, changes in frontal configuration, and variability in the soliton field. The highly-coupled nature of the acoustic mode propagation prevents detailed tomographic inversion. Instead, methods based on only the wander of the mode arrivals are used to estimate path-averaged temperatures and internal tide "strength". The modal phase structure function is introduced as a useful proxy for acoustic coherence, and is related via an integral transform to the environmental sound speed correlation function. Advantages of the method are its flexibility and division of the problem into independent contributions, such as from the water column and seabed.

Description: Office of Naval Research for providing funding for this thesis through AASERT Grant N00014-96-1-0918, and through ONR Grant N00014-98-1-0059.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1999

Description: In this thesis the analysis of natural ice events is carried out based on direct measurements of ice-borne seismo-acoustic waves generated by ice fracturing processes. A major reason for studying this phenomenon is that this acoustic emission is a significant contributor to Arctic ocean ambient noise. Also the Arctic contains rich mineral and oil resources and in order to design mining facilities able to withstand the harsh environmental conditions, we need to have a better understanding of the processes of sea ice mechanics. The data analyzed in this thesis were collected during the Sea Ice Mechanics Initiative SIMI’94 experiment which was carried out in the spring of 1994 in the Central Arctic. One of the contributions of this thesis was the determination of the polarization characteristics of elastic waves using multicomponent geophone data. Polarization methods are well known in seismology, but they have never been used for ice event data processing. In this work one of the polarization methods so called Motion Product Detector method has been successfully applied for localization of ice events and determination of polarization characteristics of elastic waves generated by fracturing events. This application demonstrates the feasibility of the polarization method for ice event data processing because it allows one to identify areas of high stress concentration and "hot spots" in ridge building process. The identification of source mechanisms is based on the radiation patterns of the events. This identification was carried out through the analysis of the seismo-acoustic emission of natural ice events in the ice sheet. Previous work on natural ice event identification was done indirectly by analyzing the acoustic energy radiated into the water through coupling from elastic energy in the ice sheet. After identification of the events, the estimation of the parameters of fault processes in Arctic ice is carried out. Stress drop, seismic moment and the type of ice fracture are determined using direct near-field measurements of seismo-acoustic signals generated by ice events. Estimated values of fracture parameters were in good agreement with previous work for marginal ice zone. During data processing the new phenomenon was discovered: "edge waves", which are waves propagating back and forth along a newly opened ice lead. These waves exhibit a quasi-periodic behavior suggesting some kind of stick-slip generation mechanism somewhere along the length of the lead. The propagation characteristics of these waves were determined using seismic wavenumber estimation techniques. In the low frequency limit the dispersion can be modeled approximately by an interaction at the lead edges of the lowest order, antisymmetric modes of the infinite plate.

Description: Support for this thesis was provided by Office of Naval Research.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1999

Description: An algorithm is developed for underwater acoustic signal processing with an array of hydrophones. With various acoustic signals coming from different directions, the maximum likelihood approach is used to estimate the source bearings and time series. Simulated annealing is used to implement the resulting time-domain beamformer. Broadband signals in spatially correlated noise are treated. Previous time-domain beamformers did not consider the correlation between random noise, and they did not use the concept of maximum likelihood, which is asymptotically optimal. We show that improved resolution can be achieved using this new method.

Description: Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1988

Description: Two approaches to determining the ocean sound speed profile using measured acoustic modal eigenvalues are examined. Both methods use measured eigenvalues and mode dependent assumed values of the WKB phase integral as input data and use the WKB phase integral as a starting point for relating the index of refraction to depth. Inversion method one is restricted to monotonic or symmetric sound speed profiles and requires a measurement of the sound speed at one depth to convert the index of refraction profile to a sound speed profile. Inversion method two assumes that the sound speed at the surface and the minimum sound speed in the profile are known and is applicable to monotonic profiles and to general single duct sound speed profiles. For asymmetric profiles, inversion method two gives the depth difference between two points of equal sound speed in the portion of the profile having two turning points, and in the remainder of the profile it gives sound speed versus depth directly. A numerical implementation of the methods is demonstrated using idealized ocean sound speed profiles numerical experiments used to test the performance of the inversions using noisy data. The two methods are used to determine the sediment sound speed profiles in two shallow water waveguide models, and inversion method one is used to find the sediment sound speed profile using data from an experiment performed in the Gulf of Mexico.

Description: Funding through the Office of Naval Research Fellowship Program.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2011

Description: Current underwater acoustic channel estimation techniques generally apply linear MMSE estimation. This approach is optimal in a mean square error sense under the assumption that the impulse response fluctuations are well characterized by Gaussian statistics, leading to a Rayleigh distributed envelope. However, the envelope statistics of the underwater acoustic communication channel are often better modeled by the K-distribution. In this thesis, by presenting and analyzing field data to support this claim, I demonstrate the need to investigate channel estimation algorithms that exploit K-distributed fading statistics. The impact that environmental conditions and system parameters have on the resulting distribution are analyzed. In doing so, the shape parameter of the K-distribution is found to be correlated with the source-to-receiver distance, bandwidth, and wave height. Next, simulations of the scattering behavior are carried out in order to gain insight into the physical mechanism that cause these statistics to arise. Finally, MAP and MMSE based algorithms are derived assuming K-distributed fading models. The implementation of these estimation algorithms on simulated data demonstrates an improvement in performance over linear MMSE estimation.

Description: This work was supported by the Office of Naval Research grant #N00014-05-10085 and the National Science Foundation grant #OCE-0519903.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 8, 1988

Description: Several experiments are presented in this thesis which examine methods to measure and monitor fluid flow from hydrothermal vent fields. Simultaneous velocity, temperature, and conductivity data were collected in the convective flow emanating from a hydrothermal vent field located at 10°S6'N, 103° 41'W on the East Pacific rise. The horizontal profiles obtained indicate that the flow field approaches an ideal plume in the temperature and velocity distribution. Such parameters as total heat flow and maximum plume height can be estimated using either the velocity or the temperature information. The results of these independent calculations are in close agreement, yielding a total heat flow from this vent site of 3.7 ± 0.8 MW and a maximum height of 150±10 m. The nonlinear effects of large temperature variations on heat capacity and volume changes slightly alter the calculations applied to obtain these values. In Guaymas Basin, a twelve day time series of temperature data was collected from a point three centimeters above a diffuse hydrothermal flow area. Using concurrent tidal gauge data from the town of Guaymas it is shown that the effects of tidar currents can be strong enough to dominate the time variability of a temperature signal at a fixed point in hydrothermal flow and are a plausible explanation for the variations seen in the Guaymas Basin temperature data. Theoretical examination of hot, turbulent, buoyant jets exiting from hydrothermal chimneys revealed acoustic source mechanisms capable of producing sound at levels higher than ambient ocean noise. Pressure levels and frequency generated by hydrothermal jets are dependent on chimney dimensions, fluid velocity and temperature and therefore can be used to monitor changes in these parameters over time. A laboratory study of low Mach number jet noise and amplification by flow inhomogeneities confirmed theoretical predictions for homogeneous jet noise power and frequency. The increase in power due to convected flow inhomogeneities, however, was lower in the near field than expected. Indirect evidence of hydrothermal sound fields (Reidesel et al., 1982; Bibee and Jacobson, 1986) showing anomalous high power and low frequency noise associated with vents is due to processes other than jet noise. On Axial Seamount, Juan de Fuca Ridge, high quality acoustic noise measurements were obtained by two hydrophones located 3 m and 40 m from an active hydrothermal vent, in an effort to determine the feasibility of monitoring hydrothermal vent activity through floW noise generation. Most of the noise field could be attributed to ambient ocean noise sources of microseisms, distant shipping and weather, punctuated by local ships and biological sources. Water/rock interface waves of local origin, were detected which showed high pressure amplitudes near the seafloor and, decaying with vertical distance, produced low pressures at 40 m above the bottom. Detection of vent signals was hampered by unexpected spatial non- stationarity due to shadowing effects of the caldera wall. No continuous vent signals were deemed significant based on a criterion of 90% probability of detection and 5% probability of false alarm. However, a small signal near 40 Hz, with a power level of 1x10-4 Pa2/Hz was noticed on two records taken near the Inferno black smoker. The frequency of this signal is consistent with predictions and the power level suggests the occurrence of jet noise amplification due to convected density inhomogeneities. Ambient noise from the TAG (Trans-Atlantic Geotraverse) hydrothermal area on the Mid-Atlantic Ridge near 26°N, in the frequency band 1-30 Hz at a range of 0.75-14 km from the site of an extremely active high temperature hydrothermal vent field (Rona, 1986) was examined. The ambient noise field exhibits great temporal and spatial variations attributed in part to typical ocean noise sources such as distant shipping and microseisms. Power spectral levels as measured at each of six ocean bottom hydrophones (OBH) were used to estimate the location of point sources of sound in the area, if any. The hydrothermal vent did not produce enough sound to be located as a point source using data from the OBH array. The only consistently identifiable point source found with the data set was generating sound in a 0.8-3.5 Hz bandwidth and located outside the median valley. It appears to be harmonic tremor associated with the tip of a ridge on the western side of the spreading axis and may be volcanic in origin.

Description: This work was supported by the WHOI/MIT Education Office, the Center for Analysis of Marine Systems, the National Science Foundation (grant OCE83-l0l75), NOAA National Sea Grant College Program Office, Dept. of Commerce under grant #NA86-AA-D-SG090, WHOI Sea Grant (R/6-l4), the Office of Naval Research grant #N0014-87-K-0007, and the NOAA Vents Program.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1998

Description: In practical applications with bathymetric sidescan sonars, the multipath reflections and other directional interferences are the key limiting factors for a better performance. This thesis proposes a new scheme to deal with the interferences using a multiple-row bathymetric sidescan sonar. Instead of smoothing the measurements over some time or angle intervals, which was previously widely investigated, we resolve the multipath interferences from the direct signal. Two approaches on signal direction-of-arrival DOA and amplitude estimation are developed, the correlated signal direction estimate CSDE for three-row systems and the ESPRIT-based method. These approaches are compared using different sonar data models, including a stochastic model from the statistical analysis on bottom scattering and a coherent model from the analysis on interference field; the simulations show the ESPRIT-based approach is quite robust at the angular separation of 100 between two sources and at the signal-to-noise ratio above 10dB except for highly coherent or temporally correlated signals, for which CSDE works very well. The computer simulation results and the discussions on practical algorithm implementation indicate the proposed scheme can be applied to a real multiple-row bathymetric sidescan sonar. With the capability to simultaneously resolve two or more directional signals, the new sonar model should work better for a wider variety of practical situations in shallow water with out significant increase of the system cost.

Description: Funding supporting my thesis research project was provided by the Office of Naval Research ONR.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1988

Description: In order to determine the efficacy of tomographic reconstructions of the ocean sound speed structure in improving acoustic field predictions for source localization, a 150 km by 350 km volume of ocean 3000 meters deep was synthetically modeled to be similar to the Gulf Stream system, including an eddy and a front. The features were Gaussian, with the eddy's maximum sound speed perturbation being 10ms-1 and the front's maximum perturbation 15ms-1. Two vertical slices through this system were inverted in a synthetic tomography experiment using linear optimal estimation theory. Inversions were also performed using XSV and satellite sea surface temperature data. Gaussian fits to the reconstructed features were constructed for use with a three dimensional raytrace program (HARPO). Three dimensional rays were propagated both through the reconstructions and the original model. Travel time versus intensity (transmission loss) for the eigenrays was used as a basis for intercomparison. Tomographic results showed good reconstruction for a first iteration of the inversion, but inadequate vertical resolution. Iterations and the use of more refractive eigenrays are needed for improvement of the reconstruction, especially for the front. Reconstructed results for the acoustic field should improve conventional beamforming, but are probably inadequate for matched field processing.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1984

Description: The distribution and feeding behavior of bacterivorous micro flagellates (2-20 μm protozoa) and their ingestion by copepods were examined in an attempt to assess the importance of these protozoa as a trophic link between planktonic bacteria and zooplankton. The abundance of microflagellates relative to other picoplankton (0.2-2.0 μm) and nanoplankton (2-20 μm) populations in water samples in the North Atlantic and in Lake Ontario and on macroaggregates in the North Atlantic was determined using direct microscopical and culture estimation techniques. Seasonal, vertical and geographical changes in the density of microflagellates were generally not greater than one order of magnitude. Microscopical counts of heterotrophic nanoplankton (presumably microflagellates) typically ranged from a few hundred to a few thousand m1-1 for a variety of planktonic environments. They constituted approximately 1/3 to 1/2 of the nanoplankton in the euphotic zone and dominated the nanoplankton in the aphotic zone. Most Probable Number (MPN) estimation of the density of bacterivorous protozoa indicated that microflagellates were, on average, an order of magnitude more abundant than bacterivorous ciliates and amoebae. MPN and direct microscopical counts of microflagellates differed by as much as 104. This discrepancy was smaller in eutrophic environments (e.g. Continental Shelf and Lake Ontario) and on macroscopic detrital aggregates. All microbial populations enumerated were highly concentrated on macroscopic detrital aggregates relative to their abundance in the water surrounding the aggregates. Enrichment factors (the ratio of abundance of a population on a macroaggregate to its abundance in the surrounding water) increased along a eutrophic-to-oligotrophic gradient because of the combined effects of an increased abundance of microorganisms on macroaggregates in oligotrophic environments and a decreased abundance in the surrounding water in these same environments. Average enrichment factors for direct microscopical counts of heterotrophic nanoplankton (range = 17-114) were not as large as enrichment factors observed for MPN estimates of the number of bacterivorous microflagellates (range = 273-18400). Microflagellates numerically dominated the bacterivorous protozoa cultured from macroaggregates by one to two orders of magnitude, but ciliates and amoebae were also highly enriched on macroaggregates. Microenvironments are therefore a potentially important aspect for the ecology of planktonic microorganisms. Observations on the microbial colonization of mucus sloughed by ctenophores and discarded appendicularian houses suggest that these materials may be important sources of macroaggregates. Batch and continuous culture experiments were conducted with clonal cultures of microflagellates to test their ability to grow on various types and densities of bacteria. The doubling time of Monas sp. 1 ranged from 43 hr (when fed the cyanobacterium Synechococcus Strain WH 8101) to 6.9 hr (when fed the heterotrophic bacterium Serratia marinorubra). Cell yields (i.e. the conversion of bacterial biomass into protozoan biomass) of Monas sp. 1 fed two species of heterotrophic bacteria were greater than yields for the microflagellate fed two species chroococcoid cyanobacteria (range = 7-68%). Cell yields of two other species of microflagellates (Monas sp. 2 and Cryptobia maris) were 48% and 61%, respectively, on the bacterium Pseudomonas halodurans. Microflagellates grew in continuous culture at concentrations of bacteria which were lower than bacterial densities required for the growth of ciliates as shown by other investigations. Therefore, microflagellates appear to be well-adapted for grazing bacterioplankton. Microflagellates were also investigated for their ability to graze bacteria attached to particles. Bodo nanorensis and Rhynchomonas nasuta both showed a marked ability to graze attached bacteria and a limited ability to graze unattached cells. These results suggest that microflagellates may also be important consumers of bacteria attached to particles in the plankton and may explain the highly elevated densities of microflagellates on macroaggregates. Grazing experiments performed with the copepod Acartia tonsa indicated that heterotrophic microflagellates were ingested by the copepods at rates comparable to the ingestion of phytoplankton of similar size. The presence of heterotrophic microflagellates did not depress filtration rates of the copepods, and one species (Cryptobia maris) appeared to be selectively grazed. Survival of A. tonsa on a diet of heterotrophic microflagellates was similar to survival on a diet of phytoplankton and was significantly longer than survival of starved Controls or copepods fed only bacteria. Due to their ability to grow at in-situ densities of planktonic bacteria, their relatively high cell yields, and their acceptability as food for zooplankton, it is concluded that bacterivorous microflagellates may constitute an important trophic link between bacteria and zooplankton. This link may provide a mechanism whereby organic material and energy from the detrital food chain can be returned to the classical phytoplankton-copepod-fish food chain.

Description: This research was supported by National Science Foundation grants OCE80-2444l and OCE82-l4928 and Ocean Industry Program grant 4473 awarded to Dr. Laurence P. Madin, NSF Doctoral Dissertation grant OCE8l-l299l, the Woods Hole Oceanographic Institution Education Program and the Wood Hole Oceanographic Institution Biology Department.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1985

Description: The acoustic properties of marine sediments have a direct effect on the propagation of sound in the ocean. In the frequency range of interest (50 - 500 Hz) the sediment can be modelled as a fluid. Assuming horizontal stratification of the ocean bottom, the acoustic parameters of interest are the compressional wave speed, the compressional wave attenuation and density as a function of depth. An inverse method based on a perturbation technique is presented in this thesis for the determination of these parameters. A monochromatic source experiment is proposed because of the desirability of such an experiment for determining the acoustic properties of an anelastic medium. The input information is the plane wave reflection coerricent as a function of the angle of incidence at a fixed frequency. A nonlinear integral equation relating the variations of these acoustic properties from a known reference value to the plane wave reflection coefficient is derived. This is then linearised using the Born approximation. The region of validity of the Born approximation is derived and based on this the optimum angular aperture for the input data is obtained. The linearised integral equation is a Fredholm integral equation of the first kind. An acceptable stable solution of the integral equation is obtained by imposing a priori constraints on the solution. The inversion method is tested using synthetic data and inversions are carried out for various examples of the attenuation coefficient profile and the sound speed profile. The results obtained with noise free data show good agreement between the true profiles and the reconstructed profiles. The resolution obtainable with the data set is studied using the resolving power theory of Backus and Gilbert and the inversion method is shown to provide adequate resolution. The effect of additive noise in data is examined and inversions performed with noisy data yielded stable acceptable results.

Description: I acknowledge the financial support provided by the education office in the Woods Hole Oceanographic Institution and the Office of Naval Research.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1986

Description: The dual issues of modal decomposition for tonal sound fields and the temporal coherence of the modal amplitudes are investigated for the case of the central Arctic sound channel at very low frequencies (15-80 Hz). A detailed study of the Arctic modal structure for these frequencies reveals the central role played by the strong Arctic surface duct. The performance of each of four different modal beamforming algorithms when applied to the vertical array deployed during the FRAM IV Arctic Acoustic Experiment is analyzed. A multiple beam (or decoupled beam) least squares processor produces the most acceptable results for Arctic conditions. The modal decomposition is sensitive to vertical array tilt caused by hydrodynamic drag; a technique for its estimation from the acoustie data is developed. Tonal data taken from both the horizontal and vertical arrays deployed during FRAM IV is analyzed. Horizontal array results confirm the modal amplitudes generated from vertical array data. The rough surface scattering from the ice canopy places an upper limit of 40 Hz on efficient surface duct propagation. Attenuation measurements for the first mode show excellent agreement with predictions made for ice scattering using the method of small perturbations and experimental ice statistics. The high levels of coherence observed (O.95 to 0.99) show that tonal signal propagation in the Arctic channel is essentially deterministic for time periods well in excess of one hour. The various modes may then be considered to maintain a constant phase relationship over time.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1991

Description: Breaking waves dissipate energy, transfer momentum from the wind to surface currents and breaking enhances the transfer of gas and mass across the air-sea interface. Breaking waves are believed to be the dominant source of sea surface sound at frequencies greater than 500 Hz and the presence of breaking waves on the ocean surface has been shown to enhance the scattering of microwave radiation. Previous studies have shown that breaking waves can be detected by measuring the microwave backscatter and acoustic radiation from breaking waves. However, these techniques have not yet proven effective for studying the dynamics of breaking. The primary motivation for the research presented in this thesis was to determine whether measurements of the sound generated by breaking waves could be used to quantitatively study the dynamics of the breaking process. Laboratory measurements of the microwave backscatter and acoustic radiation from two-dimensional breaking waves are described in Chapter 2. The major findings of this Chapter are: 1) the mean square acoustic pressure and backscattered microwave power correlate with the wave slope and dissipation for waves of moderate slope, 2) the mean square acoustic pressure and backscattered microwave power correlate strongly with each other, and 3) the amount of acoustic energy radiated by an individual breaking event scaled with the amount of mechanical energy dissipated by breaking. The observed correlations with the mean square acoustic pressure are only relevant for frequencies greater than 2200 Hz because lower frequencies were below the first acoustic cut-off frequency of the wave channel. In order to study the lower frequency sound generated by breaking waves another series of two-dimensional breaking experiments was conducted. Sound at frequencies as low as 20 Hz was observed and the mean square acoustic pressure in the frequency band from 20 Hz-l kHz correlated strongly with the wave slope and dissipation. A characteristic low frequency signal was observed immediately following the impact of the plunging wave crest. The origin of this low frequency signal was found to be the pulsating cylinders of air which are entrained by the plunging waves. The pulsation frequency correlated with both the wave slope and dissipation. Following the characteristic constant frequency signal, approximately 0.25 s after the initial impact of the plunging crest, another low frequency signal was typically observed. These signals were generally lower in frequency initially and then increased in frequency as time progressed. To determine if three-dimensional effects were important in the sound generation process and to measure the sound beneath larger breaking waves a series of experiments was conducted in a large multi-paddle wave basin. Three-dimensional breaking waves were generated and the sound produced by breaking was measured in the frequency range from 10 Hz to 20 kHz. The observed sound spectra showed significant increases in level across the entire bandwidth from 10 Hz to 20 kHz and the spectra sloped at -5 to-6 dB per octave at frequencies greater than 1 kHz. The mean square acoustic pressure in the frequency band from 10 Hz to 150 Hz correlated with the wave amplitude similar to the results obtained in the two-dimensional breaking experiments. Large amplitude low frequency spectral peaks were observed approximately 0.75 s after the initial impact of the plunging crests. It was postulated that the low frequency signals observed some time after the initial impact of the plunging crests for both the two and three-dimensional breakers were caused by the collective oscillation of bubble clouds. Void fraction measurements taken by Eric Lamarre were available for five breaking events and therefore the average sound speed inside the bubble clouds and their radii were known. Using this information the resonant frequencies of a two-dimensional cylindrical bubble cloud of equal radius and sound speed were calculated. The frequencies of the observed signals matched closely with the calculated resonant frequencies of the first and second mode of the two-dimensional cylindrical bubble cloud. The close agreement supports the hypothesis that the low frequency signals were produced by the collective oscillation of bubble clouds. In Chapter 4 a model of the sound produced by breaking waves is presented which uses the sound radiated by a single bubble oscillating at its linear resonant frequency and the bubble size distribution to estimate the sound spectrum. The model generates a damped sinusiodal pulse for every bubble formed, as calculated from the bubble size distribution. If the range to the receiver is known then the only unknown parameters are ε, the initial fractional amplitude of the bubble oscillation and L, the dipole moment arm or twice the depth of the bubble below the free surface. It was found that if the product εxL is independent of the bubble radius the model reproduces the shape and magnitude of the observed sound spectrum accurately. The success of the model implies that it may be possible to calculate the bubble size distribution from the sound spectrum. The model was validated using data from experiments where the breaking events were small scale gently spilling waves (Medwin and Daniel, 1990).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2001

Description: Matched-field methods concern estimation of source location and/or ocean environmental parameters by exploiting full wave modeling of acoustic waveguide propagation. Typical estimation performance demonstrates two fundamental limitations. First, sidelobe ambiguities dominate the estimation at low signal-to-noise ratio (SNR), leading to a threshold performance behavior. Second, most matched-field algorithms show a strong sensitivity to environmental/system mismatch, introducing some biased estimates at high SNR. In this thesis, a quantitative approach for ambiguity analysis is developed so that different mainlobe and sidelobe error contributions can be compared at different SNR levels. Two large-error performance bounds, the Weiss-Weinstein bound (WWB) and Ziv-Zakai bound (ZZB), are derived for the attainable accuracy of matched-field methods. To include mismatch effects, a modified version of the ZZB is proposed. Performance analyses are implemented for source localization under a typical shallow water environment chosen from the Shallow Water Evaluation Cell Experiments (SWellEX). The performance predictions describe the simulations of the maximum likelihood estimator (MLE) well, including the mean square error in all SNR regions as well as the bias at high SNR. The threshold SNR and bias predictions are also verified by the SWellEX experimental data processing. These developments provide tools to better understand some fundamental behaviors in matched-field performance and provide benchmarks to which various ad hoc algorithms can be compared.

Description: Financial support for my research was provided by the Office of Naval Research and the WHOI Education Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2000

Description: A channel characterization experiment for the underwater acoustic communication channel was carried out at Scripps Pier in May 1999. The experiment investigated acoustic transmission in very shallow water and breaking waves. In analyzing the data, several questions arose. The majority of the acoustic channel probe data was corrupted by crosstalk in the receiver array cable. This thesis investigates methods to correct for the effects of the crosstalk, to attempt to recover the channel probe data. In selected regions, the crosstalk could be removed quite effectively using a linear least-squares method to estimate the crosstalk coefficients. The bulk of the data could not be corrected, however, primarily due to crosstalk from a receiver channel which was not recorded, and hence could not be well estimated. A second question addressed by this thesis is concerned with acoustic propagation in shallow water under bubble clouds. The breaking waves injected air deep into the water column. The resulting bubble clouds heavily attenuated acoustic signals, effectively causing total dropouts of the acoustic communication channel. Due to buoyancy, the bubbles gradually rise, and the communication channel clears. The channel clearing was significantly slower than predicted by geometric ray acoustic propagation models, however. Proposed explanations included secondary, unobserved, breaking events causing additional bubble injection; delayed rising of bubbles due to turbulent currents; or failure of the geometric ray model due to suppression by bubble clouds of acoustic signals which are not along the geometric ray paths. This thesis investigated the final hypothesis, modeling the acoustic propagation in Scripps Pier environment, using the full wave equation modeling package OASES. It was determined that the attenuation of the propagating acoustic signal is not accurately predicted by the bubble-induced attenuation along the geometric ray path.

Description: For financial support, thanks to the National Science Foundation for funding me on a Graduate Research Fellowship, and thanks to the WHOI Education Office for supplementing that fellowship.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1987

Description: This thesis presents the theoretical and computational underpinnings of a novel approach to the determination of the acoustic parameters of the ocean bottom using a monochromatic source. The problem is shown to be equivalent to that of the reconstruction of the potential in a Schrodinger equation from the knowledge of the plane-wave reflection coefficient as a function of vertical wavenumber, r(kz) for all real positive k z. First, the reflection coefficient is shown to decay asymptotically at least as fast as (1/kz2) for large kz and is therefore inteqrable. The Gelfand-Levitan inversion procedure is extended to include the case of basement velocity higher than the velocity of sound in water. The neglect of bound states is shown to be justified in both clayey silt and silty clay at the 220 Hz frequency of operation. Three methods for the numerical solution of the integral equation are investigated. The first one is an "Improved Born approximation" wherein the solution is given as a series expansion the first term of which is the Born approximation while the second term represents a substantial and yet easy to implement improvement over Born. The two other methods are based on a discretization of the Gelfand-Levitan integral equation, and both avoid a matrix inversion: one by employing a recursive procedure, and the other by coupling the Gelfand-Levitan equation with a partial differential equation. Bounds are obtained on errors in the solution due either to discretization or to data inaccuracy. These methods are tested on synthetic data obtained from known geoacoustic models of the ocean bottom. Results are found to be very accurate particularly at the top of the sediment layer with resolution of less than the wavelength of the acoustic source in the water. Several effects are investigated, such as sampling, attenuation, and noise. Also examined is the gradual restriction of the reflection coefficient to a finite range of vertical wave numbers and the consequent progressive deterioration of the reconstruction. The analysis shows how to reconstruct velocity profiles in the presence of density variation when the experiment is conducted at two frequencies. Our results provide a good understanding of the issues involved in conducting a monochromatic deep ocean bottom experiment and constitute a promising technique for processing the experimental data when it becomes available.

Description: Support for this thesis was provided in part by the education office at WHOI and by the Office of Naval Research.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2002

Description: One of the major problems in wireless communications is compensating for the time-varying intersymbol interference (ISI) due to multipath. Underwater acoustic communications is one such type of wireless communications in which the channel is highly dynamic and the amount of ISI due to multipath is relatively large. In the underwater acoustic channel, associated with each of the deterministic propagation paths are macro-multipath fluctuations which depend on large scale environmental features and geometry, and micro-multipath fluctuations which are dependent on small scale environmental inhomogeneities. For arrivals which are unsaturated or partially saturated, the fluctuations in ISI are dominated by the macro-multipath fluctuations resulting in correlated fluctuations between different taps of the sampled channel impulse response. Traditional recursive least squares (RLS) algorithms used for adapting channel equalizers do not exploit this structure. A channel subspace post-filtering algorithm that treats the least squares channel estimate as a noisy time series and exploits the channel correlation structure to reduce the channel estimation error is presented. The improvement in performance of the algorithm with respect to traditional least squares algorithms is predicted theoretically, and demonstrated using both simulation and experimental data. An adaptive equalizer structure that explicitly uses this improved estimate of the channel impulse response is discussed. The improvement in performance of such an equalizer due to the use of the post-filtered estimate is also predicted theoretically, and demonstrated using both simulation and experimental data.

Description: This research was supported by an ONR Graduate Traineeship Award Grant #N00014-00-10049.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2009

Description: A confluence of several coastal oceanographic features creates an acoustically interesting region with high variability along the New England Shelfbreak. Determining the effect of the variability on acoustic propagation is critical for sonar systems. In the Nantucket Shoals area of the Middle Atlantic Bight, two experiments, the New England Shelfbreak Tests (NEST), were conducted in May and June, 2007 and 2008, to study this variability. A comprehensive climatology of the region along with the experimental data provided detailed information about the variability of the water column, particularly the temperature and sound speed fields. Empirical orthogonal function (EOF) analysis of the ocean sound speed field defined a set of perturbations to the background sound speed field for each of the NEST Scanfish surveys. Attenuation due to bottom sediments is the major contributor of transmission loss in the ocean. In shallow water, available propagation paths most often include bottom interaction. Perturbations in the ocean sound speed field can cause changes in the angle of incidence of sound rays with the bottom, which can result in changes to the amount of sound energy lost to the bottom. In lieu of complex transmission loss models, the loss/bounce model provides a simpler way to predict transmission loss changes due to perturbations in the background sound speed field in the ocean. Using an acoustic wavenumber perturbation method, sound speed perturbations, defined by the ocean EOF modes, are translated into a change in the horizontal wavenumber, which in turn changes the modal angle of incidence. The loss/bounce model calculates the loss of sound energy (dB) per bottom bounce over a given distance based on the change in angle of incidence. Evaluated using experimental data from NEST, the loss/bounce model provided accurate predictions of changes to transmission loss due to perturbations of the background sound speed field.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2009

Description: Mode filtering is most commonly implemented using the sampled mode shape or pseudoinverse algorithms. Buck et al placed these techniques in the context of a broader maximum a posteriori (MAP) framework. However, the MAP algorithm requires that the signal and noise statistics be known a priori. Adaptive array processing algorithms are candidates for improving performance without the need for a priori signal and noise statistics. A variant of the physically constrained, maximum likelihood (PCML) algorithm is developed for mode filtering that achieves the same performance as the MAP mode filter yet does not need a priori knowledge of the signal and noise statistics. The central innovation of this adaptive mode filter is that the received signal's sample covariance matrix, as estimated by the algorithm, is constrained to be that which can be physically realized given a modal propagation model and an appropriate noise model. The first simulation presented in this thesis models the acoustic pressure field as a complex Gaussian random vector and compares the performance of the pseudoinverse, reduced rank pseudoinverse, sampled mode shape, PCML minimum power distortionless response (MPDR), PCML-MAP, and MAP mode filters. The PCML-MAP filter performs as well as the MAP filter without the need for a priori data statistics. The PCML-MPDR filter performs nearly as well as the MAP filter as well, and avoids a sawtooth pattern that occurs with the reduced rank pseudoinverse filter. The second simulation presented models the underwater environment and broadband communication setup of the Shallow Water 2006 (SW06) experiment. Data processing results are presented from the Shallow Water 2006 experiment, showing the reduced sensitivity of the PCML-MPDR filter to white noise compared with the reduced rank pseudoinverse filter. Lastly, a linear, decision-directed, RLS equalizer is used to combine the response of several modes and its performance is compared with an equalizer applied directly to the data received on each hydrophone.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009

Description: Marine mammal whistle calls present an attractive medium for covert underwater communications. High quality models of the whistle calls are needed in order to synthesize natural-sounding whistles with embedded information. Since the whistle calls are composed of frequency modulated harmonic tones, they are best modeled as a weighted superposition of harmonically related sinusoids. Previous research with bottlenose dolphin whistle calls has produced synthetic whistles that sound too “clean” for use in a covert communications system. Due to the sensitivity of the human auditory system, watermarking schemes that slightly modify the fundamental frequency contour have good potential for producing natural-sounding whistles embedded with retrievable watermarks. Structured total least squares is used with linear prediction analysis to track the time-varying fundamental frequency and harmonic amplitude contours throughout a whistle call. Simulation and experimental results demonstrate the capability to accurately model bottlenose dolphin whistle calls and retrieve embedded information from watermarked synthetic whistle calls. Different fundamental frequency watermarking schemes are proposed based on their ability to produce natural sounding synthetic whistles and yield suitable watermark detection and retrieval.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2002

Description: Sound propagation in shallow water is highly dependent on the interaction of the sound field with the bottom. In order to fully understand this problem, it is necessary to obtain reliable estimates of bottom geoacoustic properties that can be used in acoustic propagation codes. In this thesis, perturbative inversion methods and exact inverse methods are discussed as a means for inferring geoacoustic properties of the bottom. For each of these methods, the input data to the inversion is the horizontal wavenumber spectrum of a point-source acoustic field. The main thrust of the thesis work concerns extracting horizontal wavenumber content for fully three-dimensionally varying waveguide environments. In this context, a high-resolution autoregressive (AR) spectral estimator was applied to determine wavenumber content for short aperture data. As part of this work, the AR estimator was examined for its ability to detect discrete wavenumbers in the presence of noise and also to resolve closely spaced wavenumbers for short aperture data. As part of a geoacoustic inversion workshop, the estimator was applied to extract horizontal wavenumber content for synthetic pressure field data with range-varying geoacoustic properties in the sediment. The resulting wavenumber content was used as input data to a perturbative inverse algorithm to determine the sound speed profile in the sediment. It was shown using the high-resolution wavenumber estimator that both the shape and location of the range-variability in the sediment could be determined. The estimator was also applied to determine wavenumbers for synthetic data where the water column sound speed contained temporal variations due to the presence of internal waves. It was shown that reliable estimates of horizontal wavenumbers could be obtained that are consistent with the boundary conditions of the waveguide. The Modal Mapping Experiment (MOMAX), an experimental method for measuring the full spatial variability of a propagating sound field and its corresponding modal content in two-dimensions, is also discussed. The AR estimator is applied to extract modal content from the real data and interpreted with respect to source/receiver motion and geometry. For a moving source, it is shown that the wavenumber content is Doppler shifted. A method is then described that allows the direct measure of modal group velocities from Doppler shifted wavenumber spectra. Finally, numerical studies are presented addressing the practical issues associated with using MOMAX type data in the exact inversion method of Gelfand-Levitan.

Description: I am especially grateful to ONR for providing the funding for me to do this work.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2009

Description: Trichodesmium is a colonial, N2-fixing cyanobacterium found in tropical oceans. Species of Trichodesmium are genetically similar but several species exist together in the same waters. In order to coexist, Trichodesmium spp. may occupy different niche spaces through differential utilization of resources such as nutrients and light, and through responses to physical characteristics such as temperature and turbulence. To investigate niche differentiation in Trichodesmium, I characterized cultured strains of Trichodesmium, identified and enumerated Trichodesmium clades in the field, and investigated P stress and N2 fixation in field populations. Species of Trichodesmium grouped into two clades based on sequences from 16S rDNA, the internal transcribed spacer (ITS), and the heterocyst differentiation gene hetR. Clade I contained Trichodesmium erythraeum and Trichodesmium contortum, and clade II contained Trichodesmium thiebautii, Trichodesmium tenue, Trichodesmium hildebrandtii, and Trichodesmium pelagicum. Each clade was morphologically diverse, but species within each clade had similar pigmentation. I developed a quantitative polymerase chain reaction (qPCR) method to distinguish between these two clades. In field populations of the Atlantic and Pacific Oceans, the qPCR method revealed that clade II Trichodesmium spp. were more prominent than clade I in the open ocean. Concentrations of Trichodesmium did not correlate with nutrient concentrations, but clade I had wider temperature and depth distributions than clade II. Temperature and light are physical characteristics that may define niche spaces for species of Trichodesmium. Clade I and II concentrations correlated with each other in the Pacific but not in the Atlantic, indicating that the two clades were limited by the same factors in the Pacific while different factors were limiting the abundance of the two clades in the Atlantic. Trichodesmium populations in the North Atlantic were more P stressed and had higher N2 fixation rates than populations in the western Pacific. While nutrient concentrations didn’t directly correlate with Trichodesmium concentrations, the contrasting nutrient regimes found in the Atlantic and Pacific Oceans might influence distributions of the two clades differently. Unraveling the differences among species of Trichodesmium begins to explain their coexistence and enables us to understand factors controlling global N2 fixation.

Description: National Science Foundation (NSF) Biocomplexity Program Grant (OCE-0323332); the Center for Microbial Oceanography Research and Education (C-MORE), an NSF Science and Technology Center (EF-0424599); the Woods Hole Oceanographic Institution (WHOI) Ocean Life Institute (OLI) grant to J. Waterbury, and the WHOI Academic Programs Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2007

Description: This thesis covers a comprehensive analysis of long-range, deep-ocean, low-frequency, sound propagation experimental results obtained from the North Pacific Ocean. The statistics of acoustic fields after propagation through internal-wave-induced sound-speed fluctuations are explored experimentally and theoretically. The thesis starts with the investigation of the North Pacific Acoustic Laboratory 98-99 data by exploring the space-time scales of ocean sound speed variability and the contributions from different frequency bands. The validity of the Garret & Munk internal-wave model is checked in the upper ocean of the eastern North Pacific. All these results impose hard bounds on the strength and characteristic scales of sound speed fluctuations one might expect in this region of the North Pacific for both internal-wave band fluctuations and mesoscale band fluctuations. The thesis then presents a detailed analysis of the low frequency, broadband sound arrivals obtained in the North Pacific Ocean. The observed acoustic variability is compared with acoustic predictions based on the weak fluctuation theory of Rytov, and direct parabolic equation Monte Carlo simulations. The comparisons show that a resonance condition exists between the local acoustic ray and the internal wave field such that only the internal-waves whose crests are parallel to the local ray path will contribute to acoustic scattering: This effect leads to an important filtering of the acoustic spectra relative to the internal-wave spectra. We believe that this is the first observational evidence for the acoustic ray and internal wave resonance. Finally, the thesis examined the evolution with distance, of the acoustic arrival pattern of the off-axis sound source transmissions in the Long-range Ocean Acoustic Propagation EXperiment. The observations of mean intensity time-fronts are compared to the deterministic ray, parabolic equation (with/without internal waves) and (one-way coupled) normal mode calculations. It is found the diffraction effect is dominant in the shorter-range transmission. In the longer range, the (internal wave) scattering effect smears the energy in both the spatial and temporal scales and thus has a dominant role in the finale region.

Description: The funding that made this research possible came from the Office of Naval Research, and the WHOI Academic Programs Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2003

Description: A novel distributed underwater acoustic networking (UAN) protocol suitable for ad-hoc deployments of both stationary and mobile nodes dispersed across a relatively wide coverage area is presented. Nodes are dynamically clustered in a distributed manner based on the estimated position of one-hop neighbor nodes within a shallow water environment. The spatial dynamic cellular clustering scheme allows scalable communication resource allocation and channel reuse similar in design to land-based cellular architectures, except devoid of the need for a centralized controlling infrastructure. Simulation results demonstrate that relatively high degrees of interference immunity, network connectivity, and network stability can be achieved despite the severe limitations of the underwater acoustic channel.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2002

Description: This thesis investigates the complexities of acoustic scattering by finite bodies in general and by fish in particular through the development of an advanced acoustic scattering model and detailed laboratory acoustic measurements. A general acoustic scattering model is developed that is accurate and numerically effcient for a wide range of frequencies, angles of orientation, irregular axisymmetric shapes and boundary conditions. The model presented is an extension of a two-dimensional conformal mapping approach to scattering by irregular, finite-length bodies of revolution. An extensive series of broadband acoustic backscattering measurements has been conducted involving alewife fish (Alosa pseudoharengus), which are morphologically similar to the Atlantic herring (Clupea harengus). A greater-than-octave bandwidth (40-95 kHz), shaped, linearly swept, frequency modulated signal was used to insonify live, adult alewife that were tethered while being rotated in 1-degree increments over all angles of orientation in two planes of rotation (lateral and dorsal/ventral). Spectral analysis correlates frequency dependencies to morphology and orientation. Pulse compression processing temporally resolves multiple returns from each individual which show good correlation with size and orientation, and demonstrate that there exists more than one significant scattering feature in the animaL. Imaging technologies used to exactly measure the morphology of the scattering features of fish include very highresolution Phase Contrast X-rays (PCX) and Computerized Tomography (CT) scans, which are used for morphological evaluation and incorporation into the scattering modeL. Studies such as this one, which combine scattering models with high-resolution morphological information and high-quality laboratory data, are crucial to the quantitative use of acoustics in the ocean.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1983

Description: Ocean acoustic tomography was proposed in 1978 by Munk and Wunsch as a possible technique for monitoring the evolution of temperature, density, and current fields over large regions. In 1981, the Ocean Tomography Group deployed four 224 Hz acoustic sources and five receivers in an array which fit within a box 300 km. on a side centered on 26°N, 70°W (southwest of Bermuda). The experiment was intended both to demonstrate the practicality of tomography as an observation tool and to extend the understanding of mesoscale evolution in the low-energy region far from the strong Gulf Stream recirculation. The propagation of 224 Hz sound energy in the ocean can be described as a set of rays traveling from source to receiver, with each ray taking a different path through the ocean in a vertical plane connecting the source and receiver. The sources transmitted a phase-coded signal which was processed at the receiver to produce a pulse at the time of arrival of the signal. Rays can be distinguished by their different pulse travel times, and these travel times change in response to variations in sound speed and current in the ocean through which the rays passed. In order to reconstruct the ocean variations from the observed travel time changes, it is necessary to specify models for both the variations and their effect on the travel times. The dependence of travel time on the oceanic sound speed and current fields can be calculated using ray paths traced by computer. The vertical structure of the sound speed and current fields in the ocean were modelled as a combination of Empirical Orthogonal Functions (EOFs) from MODE. The horizontal structure was continuous, but was constrained to have a gaussian covariance with a 100 km. e- folding scale. The resulting estimator closely resembles objective mapping as used in meteorology and physical oceanography. The tomographic system has at present only been used to estimate sound speed structure for comparison with the traditional measurements, especially the first two NOAA CTD surveys, but the method provides means for estimating density, temperature or velocity fields, and these will be produced in the future. The sound speed estimates made using the tomographic system match the traditional measurements to within the associated error bars, and there are several possibilities for improving the signal to noise ratio of the data. Given high-precision data, tomographic systems can resolve ocean structures at small scales, such as in the Gulf Stream, or at large scales, over entire ocean basins. Work is in progress to evaluate the usefulness of tomography as an observation tool in these applications.

Description: My support for the first 3 years came from an NSF graduate fellowship, and I was then supported as a research assistant by NSF Grant OCE-8017791.

Description: Submitted in partial fulfillment of the requirements for the degree of Electrical Engineer at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology June 1979

Description: For a spherical acoustic wave incident on a horizontally stratified ocean bottom, the reflected pressure field and the plane-wave reflection coefficient are related through a two-dimensional spatial-wavenumber Fourier transform. An algorithm is proposed to evaluate the plane-wave reflection coefficient from the bottom reflected field as a function of angle of incidencè. The algorithm is based on the "Projection-Slice" theorem associated with the two-dimensional Fourier transform. This technique is implemented to evaluate the plane-wave reflection coefficient for a perfectly reflecting ocean bottom and for an isovelocity-low speed ocean bottom model.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2008.

Description: In this thesis, I provide quantitative descriptions of toothed whale echolocation and foraging behavior, including assessment of the effects of noise on foraging behavior and the potential influence of ocean acoustic propagation conditions on biosonar detection ranges and whale noise exposure. In addition to presenting some novel basic science findings, the case studies presented in this thesis have implications for future work and for management. In Chapter 2, I describe the application of a modified version of the Dtag to studies of harbor porpoise echolocation behavior. The study results indicate how porpoises vary the rate and level of their echolocation clicks during prey capture events; detail the differences in echolocation behavior between different animals and in response to differences in prey fish; and show that, unlike bats, porpoises continue their echolocation buzz after the moment of prey capture. Chapters 3-4 provide case studies that emphasize the importance of applying realistic models of ocean acoustic propagation in marine mammal studies. These chapters illustrate that, although using geometric spreading approximations to predict communication/target detection ranges or noise exposure levels is appropriate in some cases, it can result in large errors in other cases, particularly in situations where refraction in the water column or multi-path acoustic propagation are significant. Finally, in Chapter 5, I describe two methods for statistical analysis of whale behavior data, the rotation test and a semi-Markov chain model. I apply those methods to test for changes in sperm whale foraging behavior in response to airgun noise exposure. Test results indicate that, despite the low-level exposures experienced by the whales in the study, some (but not all) of them reduced their buzz production rates and altered other foraging behavior parameters in response to the airgun exposure.

Description: Work presented in this thesis was supported by a National Science Foundation Graduate Research Fellowship, the WHOI Ocean Life Institute (Grant Numbers 32031300 and 25051351), the Office of Naval Research, the U.S. Department of the Interior Minerals Management Service (Cooperative Agreement Numbers 1435-01-02-CA-85186 and NA87RJ0445; WHOI Grant Number 15205601), the Industry Research Funding Coalition, and the WHOI/MIT Joint Program in Oceanography/Applied Ocean Science & Engineering (including a Fye Teaching Fellowship).

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2008

Description: Oceanographic applications of robotics are as varied as the undersea environment itself. As underwater robotics moves toward the study of dynamic processes with multiple vehicles, there is an increasing need to distill large volumes of data from underwater vehicles and deliver it quickly to human operators. While tethered robots are able to communicate data to surface observers instantly, communicating discoveries is more difficult for untethered vehicles. The ocean imposes severe limitations on wireless communications; light is quickly absorbed by seawater, and tradeoffs between frequency, bitrate and environmental effects result in data rates for acoustic modems that are routinely as low as tens of bits per second. These data rates usually limit telemetry to state and health information, to the exclusion of mission-specific science data. In this thesis, I present a system designed for communicating and presenting science telemetry from untethered underwater vehicles to surface observers. The system's goals are threefold: to aid human operators in understanding oceanographic processes, to enable human operators to play a role in adaptively responding to mission-specific data, and to accelerate mission planning from one vehicle dive to the next. The system uses standard lossy compression techniques to lower required data rates to those supported by commercially available acoustic modems (O(10)-O(100) bits per second). As part of the system, a method for compressing time-series science data based upon the Discrete Wavelet Transform (DWT) is explained, a number of low-bitrate image compression techniques are compared, and a novel user interface for reviewing transmitted telemetry is presented. Each component is motivated by science data from a variety of actual Autonomous Underwater Vehicle (AUV) missions performed in the last year.

Description: National Science Foundation Center for Subsurface Sensing and Imaging (CenSSIS ERC)

Description: Red Pompeian paintings, very famous for their deep intensity, are currently suffering from darkening. The origins of this darkening degradation are not clearly identified yet and remain a major issue for curators. In the specific case of cinnabar (HgS)-based red pigment, a photoinduced conversion into black metacinnabar is usually suspected. This work is focused on the blackening of red cinnabar paintings coated on a sparry calcite mortar. Different samples exhibiting different levels of degradation were selected upon visual observations and analyzed by synchrotron-based microanalytical techniques. Atomic and molecular compositions of the different debased regions revealed two possible degradation mechanisms. On one hand, micro X-ray fluorescence elemental maps show peculiar distributions of chlorine and sulfur. On the other hand, X-ray absorption spectroscopy performed at both Cl and S K-edges confirms the presence of characteristic degradation products: (i) Hg- Cl compounds (e.g., corderoite, calomel, and terlinguaite), which may result from the reaction with exogenous NaCl, in gray areas; (ii) gypsum, produced by the calcite sulfation, in black coatings. Metacinnabar is never detected. Finally, a cross section was analyzed to map the in-depth alteration gradient. Reduced and oxidized sulfur distributions reveal that the sulfated black coating consists of a 5-ím-thick layer covering intact cinnabar.

Description: Published

Description: 7484-7492

Description: reserved

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2006

Description: This thesis develops methods for estimating wideband shallow-water acoustic communication channels. The very shallow water wideband channel has three distinct features: large dimension caused by extensive delay spread; limited number of degrees of freedom (DOF) due to resolvable paths and inter-path correlations; and rapid fluctuations induced by scattering from the moving sea surface. Traditional LS estimation techniques often fail to reconcile the rapid fluctuations with the large dimensionality. Subspace based approaches with DOF reduction are confronted with unstable subspace structure subject to significant changes over a short period of time. Based on state-space channel modeling, the first part of this thesis develops algorithms that jointly estimate the channel as well as its dynamics. Algorithms based on the Extended Kalman Filter (EKF) and the Expectation Maximization (EM) approach respectively are developed. Analysis shows conceptual parallels, including an identical second-order innovation form shared by the EKF modification and the suboptimal EM, and the shared issue of parameter identifiability due to channel structure, reflected as parameter unobservability in EKF and insufficient excitation in EM. Modifications of both algorithms, including a two-model based EKF and a subspace EM algorithm which selectively track dominant taps and reduce prediction error, are proposed to overcome the identifiability issue. The second part of the thesis develops algorithms that explicitly find the sparse estimate of the delay-Doppler spread function. The study contributes to a better understanding of the channel physical constraints on algorithm design and potential performance improvement. It may also be generalized to other applications where dimensionality and variability collide.

Description: Financial support for this thesis research was provided by the Office of Naval Research and the WHOI Academic Program Office.

Description: Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Applied Ocean Sciences at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2007

Description: This thesis introduces an algorithm for inverting for the geoacoustic properties of the seafloor in shallow water. The input data required by the algorithm are estimates of the amplitudes of the normal modes excited by a low-frequency pure-tone sound source, and estimates of the water column sound speed profiles at the source and receiver positions. The algorithm makes use of perturbation results, and computes the small correction to an estimated background profile that is necessary to reproduce the measured mode amplitudes. Range-dependent waveguide properties can be inverted for so long as they vary slowly enough in range that the adiabatic approximation is valid. The thesis also presents an estimator which can be used to obtain the input data for the inversion algorithm from pressure measurements made on a vertical line array (VLA). The estimator is an Extended Kalman Filter (EKF), which treats the mode amplitudes and eigenvalues as state variables. Numerous synthetic and real-data examples of both the inversion algorithm and the EKF estimator are provided. The inversion algorithm is similar to eigenvalue perturbation methods, and the thesis also presents a combination mode amplitude/eigenvalue inversion algorithm, which combines the advantages of the two techniques.

Description: The funding that made this research possible came from the Office of Naval Research, and the WHOI Academic Programs Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April 1978

Description: The structure of the membrane-free nucleoid of Escherichia coli and of unfolded chromosomal DNA was investigated by sedimentation on neutral sucrose gradients after irradiation with 60Co gamma-rays and ultraviolet light (2S4nm). Irradiation both in vivo and in vitro was used as a molecular probe of the constraints on DNA~packaging in the bacterial chromosome. The extremely gentle lysis and unfolding procedures which were developed yielded undamaged, replicating genomes, thus permitting direct measurement of the formation and repair of DNA double-strand breaks at biologically-significant doses of ionizing radiation. In vitro UV-irradiation of nucleoids resulted in an increase in the observed rate of sedimentation due to the formation of an unknown photo-product. In contrast, UV-irradiation of wild-type cells in vivo showed evidence of the formation of incision breaks which resulted in the relaxation of supercoiling in the nucleoid. Strand breakage was also observed following in vivo UV-irradiation of a uvrB-5 strain, but at a lower rate and also accompanied by considerable unfolding of the chromosome. Such lesions may have been the result of direct photochemical reactions in the nucleoid, or enzyme activity associated with a uvr-independent mode of repair. The number of domains of supercoiling was estimated at 170 per genome equivalent of DNA based on measurements of relaxation caused by single-strand break formation in in vivo- and in vitro-gamma-irradiated folded chromosomes. Similar estimates based on the target size of RNA molecules responsible for maintaining the compact packaging of the nucleoid predicted negligible unfolding due to the formation of RNA single-strand breaks at doses up-to 10 Krad, and were born out by experimental measurements. Unfolding of the nucleoid in vitro by limit-digestion with RNase or by heating at 70° resulted in DNA complexes with sedimentation coefficients of 1030±59S and 625±15S respectively. The difference in these rates was apparently due to more complete deproteinization and thus less mass in the heated material. These structures are believed to represent intact, replicating genomes in the form of complex-theta structures containing 2-3 genome equivalents of DNA. The rate of formation of double-strand breaks was determined from molecular weight measurements of thermally unfolded chromosomal DNA gamma-irradiated in vitro. Break formation was linear with dose up to 10 Krad, resulting in 0.27 double-strand breaks per kilorad per genome equivalent of DNA and requiring 1080 eV/double-strand break. The influence of possible non-linear DNA conformations of these calculations is discussed. Repair of ionizing radiation damage to folded chromosomes was observed within 2-3 hours of post-irradiation incubation in growth medium. A model based on recombinational repair is proposed to explain the formation of 2200-2300S material during early stages of incubation and subsequent changes in the gradient profiles. Such behavior is not observed for post-irradiation incubation of wild-type cells in buffer or for a recA-13 strain incubated in growth medium. Association of unrepaired DNA with plasma membrane is proposed to explain the formation of a peak of rapidly sedimenting material (〉〉3100S) during the later stages of repair. Direct evidence of repair of double-strand breaks during post-irradiation incubation in growth medium was obtained from gradient profiles of DNA from RNAse-digested chromosomes. The sedimentation coefficient of broken molecules was restored to the value of unirradiated DNA after 2-3 hours of incubation, and the fraction of the DNA repaired in this fashion was equal to the fraction of cells which survived at the same dose. An average of 2.7 double-strand breaks per genome per lethal event was observed, suggesting that 1-2 double-strand breaks per genome are repairable in this strain of E. coli.

Description: Submitted in partial fulfillment of the requirements for Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2005

Description: This thesis develops and utilizes a method for analyzing data from the North Pacific Acoustic Laboratory's (NPAL) Basin Acoustic Seamount Scattering Experiment (BASSEX). BASSEX was designed to provide data to support the development of analytical techniques and methods which improve the understanding of sound propagation around underwater seamounts. The depth-dependent sound velocity profile of typical ocean waveguides force sound to travel in convergence zones about a minimum sound speed depth. This ducted nature of the ocean makes modeling the acoustic field around seamounts particularly challenging, compared to an isovelocity medium. The conical shape of seamounts also adds to the complexity of the scatter field. It is important to the U.S. Navy to understand how sound is diffracted around this type of topographic feature. Underwater seamounts can be used to conceal submarines by absorbing and scattering the sound they emit. BASSEX measurements have characterized the size and shape of the forward scatter field around the Kermit-Roosevelt Seamount in the Pacific Ocean. Kermit- Roosevelt is a large, conical seamount which shoals close to the minimum sound speed depth, making it ideal for study. Acoustic sources, including M-sequence and linear frequency-modulated sources, were stationed around the seamount at megameter ranges. A hydrophone array was towed around the seamount to locations which allowed measurement of the perturbation zone. Results from the method developed in this thesis show that the size and shape of the perturbation zone measured coincides with theoretical and experimental results derived in previous work.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2005

Description: This thesis investigates the application of acoustic measurements in the deep and shallow ocean to infer the sound velocity profile (svp) in the seabed. For the deep water ocean, an exact method based on the Gelfand-Levitan integral equation is evaluated. The input data is the complex plane-wave reflection coefficient estimated from measurements of acoustic pressure in water. We apply the method to experimental data and estimate both the reflection coefficient and the seabed svp. A rigorous inversion scheme is hence applied in a realistic problem. For the shallow ocean, an inverse eigenvalue technique is developed. The input data are the eigenvalues associated with propagating modes, measured as a function of source-receiver range. We investigate the estimation of eigenvalues from acoustic fields measured in laterally varying environments. We also investigate the errors associated with estimating varying modal eigenvalues, analogous to the estimation of time-varying frequencies in multicomponent signals, using time-varying autoregressive (TVAR) methods. We propose and analyze two AR sequential estimators, one for model coefficients, another for the zeros of the AR characteristic polynomial. The decimation of the pressure field defined in a discrete range grid is analyzed as a tool to improve AR estimation. The nonlinear eigenvalue inverse problem of estimating the svp from a sequence of eigenvalues is solved by iterating linearized approximations. The solution to the inverse problem is proposed in the form of a Kalman filter. The resolution and variance of the eigenvalue inverse problem are analyzed in terms of the Cramer-Rao lower bound and the Backus-Gilbert (BG) resolution theory. BG theory is applied to the design of shallow-water experiments. A method is developed to compensate for the Doppler deviation observed in experiments with moving sources.

Description: I am grateful for the support of my work provided by the WHOI Academic Programs Office and the Office of Naval Research.

Description: Submitted to the MIT Department of Biology and the WHOI Biology Department in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2006

Description: The physical and biological forces that drive zooplankton distribution and patchiness in an antarctic continental shelf region were examined, with particular emphasis on the Antarctic krill, Euphausia superba. This was accomplished by the application of acoustic, video, and environmental sensors during surveys of the region in and around Marguerite Bay, west of the Antarctic Peninsula, in the falls and winters of 2001 and 2002. An important component of the research involved the development and verification of methods for extracting estimates of ecologically-meaningful quantities from measurements of scattered sound. The distribution of acoustic volume backscattering at the single frequency of 120 kHz was first examined as an index of the overall biomass of zooplankton. Distinct spatial and seasonal patterns were observed that coincided with advective features. Improved parameterization was then achieved for a theoretical model of Antarctic krill target strength, the quantity necessary in scaling measurements of scattered sound to estimates of abundance, through direct measurement of all necessary model parameters for krill sampled in the study region and survey period. Methods were developed for identifying and delineating krill aggregations, allowing the distribution of krill to be distinguished from that of the overall zooplankton community. Additional methods were developed and verified for estimating the length, abundance, and biomass of krill in each acoustically-identified aggregation. These methods were applied to multifrequency acoustic survey data, demonstrating strong seasonal, inter-annual, and spatial variability in the distribution of krill biomass. Highest biomass was consistently associated with regions close to land where temperatures at depth were cool. Finally, the morphology, internal structure, and vertical position of individual krill aggregations were examined. The observed patterns of variability in aggregation characteristics between day and night, regions of high versus low food availability, and in the presence or absence of predators, together reinforced the conclusion that aggregation and diel vertical migration represent strategies to avoid visual predators, while also allowing the krill access to shallowly-distributed food resources. The various findings of this work have important implications to the fields of zooplankton acoustics and Antarctic krill ecology, especially in relation to the interactions of the krill with its predators.

Description: Funding was provided by a Fulbright Scholarship, a Natural Sciences and Engineering Research Council of Canada Post-Graduate Scholarship, an Office of Naval Research Graduate Traineeship Award in Ocean Acoustics (Grant N00014-03-1-0212), the Comer Science and Education Foundation, and the Woods Hole Oceanographic Institution (WHOI) Academic Programs Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May, 1976

Description: The acoustic-internal wave interaction in an acoustic waveguide is investigated using wave techniques. Refractive index fluctuations due to the vertical displacements of the internal waves create an inhomogeneous waveguide. The analysis uses weak scattering theory based upon the Rytov perturbation technique. It is found that the internal wave field acts as a diffraction grating in permtting only certain scattered acoustic waves to propagate through the waveguide. Since the internal waves are continuously distributed in wavenumer space, the acoustic fluctuations become a statistical average with a bias toward particular spatial internal wavelengths. The multimode nature of acoustic propagation precludes the linear relationship of internal wave statistics to acoustic amplitude and phase fluctuations. Assuming statistical independence between amplitude and phase fluctuations within a mode and between different modes, it is shown that the total phase-rate fluctuation is a weighted sum of the phase-rate fluctuations in the individual modes. Using a statistical internal wave model [C. Garrett and W. Munk, Geophys. Fluid Dynam., 2, 225-264 (1972)] predictions of acoustic fluctuations are made. Over much of the internal wave frequency band the slope of the phase rate frequency spectrum is between -0.5 and -1.0. The depth dependence for the mean-square phase rate fluctuation has been found. Largest fluctuations occur for shallow and deep receivers. The predicted fluctuations compare favorably with experimental data.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2006

Description: Hurricanes, powerful storms with wind speeds that can exceed 80 m/s, are one of the most destructive natural disasters known to man. While current satellite technology has made it possible to effectively detect and track hurricanes, expensive 'hurricanehunting' aircraft are required to accurately classify their destructive power. Here we show that passive undersea acoustic techniques may provide a promising tool for accurately quantifying the destructive power of a hurricane and so may provide a safe and inexpensive alternative to aircraft-based techniques. It is well known that the crashing of wind-driven waves generates underwater noise in the 10 Hz to 10 kHz range. Theoretical and empirical evidence are combined to show that underwater acoustic sensing techniques may be valuable for measuring the wind speed and determining the destructive power of a hurricane. This is done by first developing a model for the acoustic intensity and mutual intensity in an ocean waveguide due to a hurricane and then determining the relationship between local wind speed and underwater acoustic intensity. Acoustic measurements of the underwater noise generated by hurricane Gert are correlated with meteorological data from reconnaissance aircraft and satellites to show that underwater noise intensity between 10 and 50 Hz is approximately proportional to the cube of the local wind speed. From this it is shown that it should be feasible to accurately measure the local wind speed and quantify the destructive power of a hurricane if its eye wall passes directly over a single underwater acoustic sensor. The potential advantages and disadvantages of the proposed acoustic method are weighed against those of currently employed techniques. It has also long been known that hurricanes generate microseisms in the 0.1 to 0.6 Hz frequency range through the non-linear interaction of ocean surface waves. Here we model microseisms generated by the spatially inhomogeneous waves of a hurricane with the non-linear wave equation where a second-order acoustic field is created by first-order ocean surface wave motion. We account for the propagation of microseismic noise through range-dependent waveguide environments from the deep ocean to a receiver on land. We compare estimates based on the ocean surface wave field measured in hurricane Bonnie with seismic measurements from Florida.

Description: Finally, I am grateful to have been awarded the Office of Naval Research Graduate Traineeship Award in Ocean Acoustics. I also thank the MIT Sea Grant office for funding portions of this research.