ALBERT

Description: This document, which is directed at the fishing sector, researchers, conservationists and fishery administrators, was developed by researchers who are members of the Specialists Group for Marine Turtle Research and conservation in the Southwestern Atlantic Ocean (SWA) in response to the urgent need to evaluate the impact generated on sea turtles by fisheries. Historically, sea turtle conservation efforts have focused almost exclusively on the protection of nesting beaches. Nevertheless, over the last decade, research has proved incidental mortality as a result of fishing activities to be one of the greatest threats to these animals. This type of interaction is not only problematic for turtles, but also generates financial losses for fishermen and businesses. In spite of the efforts that are currently underway, researchers still do not have a detailed understanding of the impact that bycatch produces on sea turtle populations in the SWA. We have a long way to go before its effects can be minimized. Further research is needed regarding the biology and ecology of the various turtle species as well as the effective application of mitigation measures. The life cycles of sea turtles are long and complex. Turtles occupy various ecosystems (nesting beaches, coastal, neritic and oceanic zones, as well as pelagic and demersal areas) throughout their lifetimes, transcending various Exclusive Economic Zones and International Waters. The five species that inhabit the SWA region perform vast feeding and reproductive migrations, traveling through areas where many different fishing fleets operate. Therefore, sea turtles in the SWA interact with virtually all fisheries. These circumstances make it necessary to carry out biological, fishing related and conservation studies on a regional level. The efficiency of the existing international and national legal instruments has yet to be determined, in terms of their effectiveness in protecting sea turtles. In some cases, legislation that is specifically related to the interaction between fisheries and turtles does exist, such as those laws requiring the mandatory use of turtle excluding devices (TEDs). There are also explicit bans on sea turtle capture. Nevertheless, none of these regulations prevent sea turtle bycatch. Although some regional legal instruments are needed, these and the existing legislation will only be effective if they are accompanied by a broader range of permanent education and control measures, to achieve the commitment of all the parties involved. The ecosystem approach is gaining popularity among fishery administration organizations. Research and conservation efforts should also be moving in that direction. A regional and international effort is required in order to compile information regarding the bycatch produced by the various types of fisheries and fleets operating in the area. The enormous increase in fishing pressure that these fleets are exerting in this area has not been accompanied by an increase in information regarding the bycatch of species that have no commercial value. Pelagic longlining is one of the fishing methods, which must be most closely monitored, due to the high levels of bycatch that it produces, as well its ample distribution throughout the region, and the high level of fishing effort that it accounts for. Coastal trawlers and gillnetters must also be considered critical players, because they too produce a large rate of bycatch. These are the three types of fisheries that are most broadly distributed throughout the region, accounting for the majority of the fishing effort. Most of the institutions that work toward sea turtle conservation in the area have only begun to address the issue of bycatch over the last decade. This timeframe is reflected in the scope and quantity of the available publications, as well as the progress of activities directed at mitigating this problem. All of the institutions that have been mentioned in this report have made the gathering of information regarding interaction between sea turtles and fisheries one of their top priorities. Some institutions are even developing working programs for monitoring fisheries and testing mitigation measures. Many of these institutions have managed to develop adequate relationships with fishermen, ship owners and administrators. Nevertheless, limited access to funding is an obstacle to the development and testing of mitigation measures. The SWA network, which is a very valuable instrument that was created in 2003, has allowed the region’s institutions and researchers to exchange information and share their experience, in addition to lending each other support in carrying out joint activities, thus strengthening sea turtle conservation efforts. The capacity demonstrated so far by the region’s researchers and institutions, testifies to their ability to continue to make progress in knowledge generation and tests of bycatch mitigation measures.

Description: Published

Description: Este documento, dirigido al sector pesquero, investigadores, conservacionistas y administradores de las pesquerías, surge como respuesta de investigadores pertenecientes al Grupo de Especialistas en Investigación y Conservación de Tortugas Marinas en el Atlántico Sud Occidental (ASO) a la urgente necesidad de evaluar el impacto de las pesquerías sobre las tortugas marinas. Históricamente, los esfuerzos referidos a la conservación de las tortugas marinas se han dirigido casi exclusivamente a proteger las playas de anidación. Sin embargo en la última década se ha podido comprobar que una de las mayores amenazas es la mortalidad incidental causada por las pesquerías. Esta interacción no implica únicamente un problema para las tortugas, sino que también genera pérdidas económicas para los pescadores y las empresas.

Description: This document, which is directed at the fishing sector, researchers, conservationists and fishery administrators, was developed by researchers who are members of the Specialists Group for Marine Turtle Research and Conservation in the Southwestern Atlantic Ocean (SWA) in response to the urgent need to evaluate the impact generated on sea turtles by fisheries. Historically, sea turtle conservation efforts have focused almost exclusively on the protection of nesting beaches. Nevertheless, over the last decade, research has proved incidental mortality as a result of fishing activities to be one of the greatest threats to these animals. This type of interaction is not only problematic for turtles, but also generates financial losses for fishermen and businesses.

Description: Cont. fotografías

Description: Published

Description: Sea Turtle, keeping

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 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: 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 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 2007

Description: Oceanic spreading centers are sites of magmatic, tectonic, and hydrothermal processes. In this thesis I present experimental and seismological constraints on the evolution of these complex regions of focused crustal accretion and extension. Experimental results from drained, triaxial deformation experiments on partially molten olivine reveal that melt extraction rates are linearly dependent on effective mean stress when the effective mean stress is low and non-linearly dependent on effective mean stress when it is high. Microearthquakes recorded above an inferred magma reservoir along the TAG segment of the Mid-Atlantic Ridge delineate for the first time the arcuate, subsurface structure of a long-lived, active detachment fault. This fault penetrates the entire oceanic crust and forms the high-permeability pathway necessary to sustain long-lived, high-temperature hydrothermal venting in this region. Long-lived detachment faulting exhumes lower crustal and mantle rocks. Residual stresses generated by thermal expansion anisotropy and mismatch in the uplifting, cooling rock trigger grain boundary microfractures if stress intensities at the tips of naturally occurring flaws exceed a critical stress intensity factor. Experimental results coupled with geomechanical models indicate that pervasive grain boundary cracking occurs in mantle peridotite when it is uplifted to within 4 km of the seafloor. Whereas faults provide the high-permeability pathways necessary to sustain high-temperature fluid circulation, grain boundary cracks form the interconnected network required for pervasive alteration of the oceanic lithosphere. This thesis provides fundamental constraints on the rheology, evolution, and alteration of the lithosphere at oceanic spreading centers.

Description: Research was funded by a MIT Presidential Fellowship and NSF grants OCE-0095936, OCE-9907224, OCE-0137329, OCE-6892222, and OCE-6897400.

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 1997

Description: A new tomographic technique is employed to investigate the structure and dynamics of the Pacific upper mantle. We invert band-center travel times of ScS reverberations and frequency-dependent travel times of direct S phases, upper-mantle guided waves such as SS and SSS, and the R1 and G1 surface waves for the 2D composite structure in the plane of two Pacific corridors. The frequency-dependent travel times of the turning and surface waves are measured from all three components of ground motion as phase delays relative to a radially-anisotropic, spherically-symmetric oceanic mantle model, and their 2D Fréchet kernels are constructed by a coupled-mode algorithm. The travel times of the primary ScSn and sScSn phases and their first-order reverberations from the 410 and 660 discontinuities are measured as individual phases and the 2D Fréchet kernels for these band-limited signals are calculated using the paraxial ray approximation. The model parameters include shear-speed variations throughout the mantle, perturbations to radial shear-wave anisotropy in the uppermost mantle, and the topography of the 410 and 660 discontinuities. We construct vertical tomograms through two mantle corridors: one between the Tonga subduction zone and Oahu, Hawaii, which traverses the central Pacific Ocean; and the other between the Ryukyu subduction zone and Oahu, which samples the northern Philippine Sea, the western Pacific, and the entire Hawaiian swell. Tests demonstrate that the data sets for the two corridors resolve the lateral structure in the upper mantle with a scale length of a few hundreds kilometers and greater but that the resolving power decreases rapidly in the lower mantle. The model for the Tonga-Hawaii corridor reveals several interesting features, the most significant being a regular pattern of high and low shear velocities in the upper mantle between Tonga and Hawaii. These variations, which are well resolved by the data set, have a horizontal wavelength of 1500 km, a vertical dimension of 700 km, and an amplitude of about 3%, and they show a strong positive correlation with seafloor topography and geoid-height variations along this corridor. The geoid highs correspond to a series of northwest-trending swells associated with the major hotspots of the Society, Marquesas, and Hawaiian Islands. Where these swells cross the corridor, they are underlain by high shear velocities throughout the uppermost mantle, so it is unlikely that their topography is supported by thermal buoyancy. This result is substantiated by the model from the Ryukyu-Hawaii corridor, which exhibits a prominent, fast region that extends beneath the entire Hawaiian swell. This anomaly, which resides in the uppermost 200-300 km of the mantle, is also positively correlated with the undulations of the Hawaiian-swell height. The other dominant features in the Ryukyu-Hawaii model include the high-velocity subducting slabs beneath the Ryukyu and Izu-Bonin seismic zones, which extend throughout the entire upper mantle; a very low-velocity in the uppermost 160 km of the mantle beneath the northern Philippine Sea, which is ascribed to the presence of extra water in this region; and a pronounced minimum in the amount of radial anisotropy near Hawaii, which is also seen along the Tonga-Hawaii corridor. A joint inversion of the data from the two corridors reveals the same anomaly pattern and clearly demonstrates that the swells in the Central Pacific are underlain by fast velocities. It is therefore implied that the topography of the swells in the central Pacific is supported by a chemical buoyancy mechanism which is generated by basaltic volcanism and the formation of its low-density peridotitic residuum. While the basaltic depletion mechanism can produce high shear velocities in the uppermost 200 km, it cannot explain the depth extent of the fast anomalies beneath the swells which, along Tonga-Hawaii corridor, extend well into the transition zone. It is therefore hypothesized that the central Pacific is underlain by a system of convective rolls that are confined above the 660-km discontinuity. It is likely that these rolls are predominantly oriented in the direction of plate motion (like "Richter rolls ") but the limited depth of the fast anomaly beneath the Hawaiian swell (200-300 km) suggests that their pattern is probably more complicated. Nevertheless, this convection pattern appears to be strongly correlated with the locations of the Tahitian, Marquesan, and Hawaiian hotspots, which raises interesting questions for Morgan's hypothesis that these hotspots are the surface manifestations of deep-mantle plumes.

Description: This research was supported by the National Science Foundation under grant EAR- 9628351 and by the Defense Special Weapons Agency under grant DSW A-F49620-95-1- 0051.

Description: Submitted in partial fulfillment of the requirements of the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2004

Description: Laterally extensive, well-developed clinoforms have been mapped in Early Cretaceous deposits located in the northeastern 27,000 km2 of the Colvile Basin, North Slope of Alaska. Using public domain 2-D seismic data, well logs, core photographs, and grain size data, depositional geometries within the Nanushuk and Torok formations were interpreted in order to constrain the transport conditions associated with progradation of the shoreline and construction of the continental margin out of detritus shed from the ancestral Brooks Range. Using STRATA, a synthetic stratigraphic modeling package, constructional clinoform geometries similar to those preserved in the North Slope clinoform volume (32,400 km3) were simulated. Sediment flux, marine and nonmarine diffusivities, and basin subsidence were systematically varied until a match was found for the foreset and topset slopes, as well as progradation rates over a 6 milion year period. The ability of STRATA to match the seismically interpreted geometries allows us to constrain measures of possible water and sediment discharges consistent with the observed development of the Early Cretaceous c1inoform suite. Simulations indicate that, in order to reproduce observed geometries and trends using constant input parameters, the subsidence rate must be very small, only a fraction of the most likely rate calculated from the seismic data. Constant sediment transport parameters can successfully describe the evolution of the prograding margin only in the absence of tectonic subsidence. However, further work is needed to constrain the absolute magnitude of these values and determine a unique solution for the NPR-A clinoforms.

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: Published

Description: From 1986 to 1991, observers on board tuna purse-seiners based in Seychelles allow analysis of data such as oceanographic parameters, aspects of tuna schools and their associated sightings, as well as fishing characteristics (success rate, catches, cpue, species composition, duration of fishing sets). Performances of the four concerned countries (France, Spain, Japan, USSR) are compared.

Description: Published

Description: Published

Description: Published

Description: Seychelles is composed of over 100 islands with a land area of approximately 455 km², centred close to 4°30'S and 55°30'E. The combined coastline is approximately 600 km long, the oceanic shelf totals about 50 000 km² and the Exclusive Economic Zone (EEZ) is over 1 370 000 km². The total population (1994 census) stands at just under 74 000. in 1994, the population registered a growth rate of 2.2%. The GDP (1994) was SR 2373.8 million, fisheries representing 4.8% of this sum. Licensing agreements for foreign fishing activities provided a yearly revenue of SR8 million. Port Victoria is seen as a prime centre for tuna fishing operations in the Indian Ocean. In the artisanal fishery just under 900 persons are working. The largest contributor to catch by vessel type are the traditional whaler vessels representing 47.8% of the total catch. Over 66.3% of the catch is by the handline method. Carangidae representing 24% and Lutjanidae 19% of total landings. There are six specific objectives to the fisheries sector policy, which aims as resource development and maximisation of potential benefits. Nearshore fishery resources are considered to be heavily exploited, however opportunities exist around the distant islands and in deeper waters off the Mahe plateau shelf. Aquaculture of molluscs and prawns is being developed and carried out. The main constraints to development are seen as the lack of skilled manpower and foreign exchange.

Description: Published

Description: This journal is published by NIOF, Alexandria, Egypt

Description: Spatial and temporal variability in the saprophytic (SB) and salt tolerant saprophytic (STSB) bacterial counts as well as total coliforms (TC), E. coli (EC) and fecal streptococci (FS) were investigated in the Egyptian surface coastal waters of Aqaba and Suez Gulfs as well as Red Sea. A total of 200 samples collected from 40 sites during January, March, May, July and September 2002 were investigated. Hydrographical parameters including water temperature (oC), salinity (S%o), dissolved oxygen (DO) and pH were also measured. According to the European and Egyptian current standards, out of 200 samples analyzed during 2002, 183 samples (91.5%) were accepted for marine recreational purposes. The obtained results indicated that water quality of the investigated coastal areas was generally affected by sewage disposal and (or) other anthropic influences. However in bathing and recreational areas, the water quality was mainly affected by the excessive human presence i.e. tourists-visitors and their recreational activities. In general, the final counts of all the investigated bacterial groups were found to be in good correlation with each other.

Description: NIOF

Description: Published

Description: NIOF, Alexandria, Egypt

Description: The present study deals with the physical and chemical characteristics of the water of Abu Za'baal Ponds. Determination of physical parameters (air and water temperatures, transparency, electrical conductivity, salinity, total solids, total dissolved solids and total suspended solids) and chemical parameters (pH, DO, BOD, COD, HCO3 -, CO3 --, Cl- , SO4 --,Ca2+, Mg2+, Na+, K+, NO2-, NO3-, NH3, PO4--, TP and SiO2-) were carried out to identify the nature and quality of the water of Abu Za'baal Ponds. The present results reveal that the values of most physical and chemical parameters were higher than those of freshwater, lower than those of saline water and in the same range of the brackishwater. Thus, the water of Abu Za'baal Ponds can be classified as brackishwater.

Description: National Institute of Oceanography and Fisheries- Alexandria, Egypt

Description: Published

Description: Shark species, both oceanic and coastal, are very common to Seychelle waters. In the past, however, the demand for shark and shark products has always been very erratic. The ever-increasing international concern for the species and potential conflicts between fishermen and conservation groups has highlighted the issue. In the Seychelles, the shark are caught by gillnets in inshore waters and by hook-and-line and purse seine offshore. Until very recently there were no regulations controlling the shark fishery, but, partly in response to initiatives by a local conservation group, fishing for sharks with nets has been banned since 1 August 1998. A review is provided of the present situation of the fishery whilst underscoring the difficulties of formulating a Management Plan based on the limited information available. The text of Chapter 82 of the Fisheries Act of 1986 is included as an appendix to the document.

Description: Published

Description: This report reviews the spiny lobster fishery on the Mahe Plateau during the 1994 - 1995 fishing season. Following the recommendations made after the 1992 fishing season, the fishery was reopened in 1993 for two months, November and December. The monitoring programme set up in 1992 was continued to gather more information on the spiny lobster stocks so as to improve the management of this resource around the Mahe Plateau. A total of 33 licenses were issued (compared to 28 in 1993); 25 on Mahe, 2 on Praslin and 6 on La Digue. A licensed fishing unit comprised, on average, of three men. Snorkelling was used by 27 fishing units as the only catching method, 3 fishing units used traps only whilst 3 fishing units combined snorkelling with the use of traps. Over the three month open season a total of 4.1 tonnes of spiny lobsters were estimated to have been landed compared to 4.2 tonnes in 1993, most landings were on Mahe (3.03 tonnes) A catch of 0.9 tonnes was landed in November, 1.2 tonnes landed in December and 2.0 tonnes landed in January. Altogether 159 trips were undertaken equivalent to 477 man-trips for the season with 28 trips in November, 63 trips in December and 68 trips in January. The snorkelling and trap capture methods represented 70.2% and 29.8% of the catch respectively. The catch per unit of effort (CPUE) for November through January was: -36 kg/trip (November), -39 kg/trip (December), -28.5 kg/trip (January). Three main species were targeted: Panulirus penicillatus (Homard Grosse Tete), Panulirus longipes (Homard Rouge), Panulirus versicolor (Homard Vert). The catch composition by fishing method was: a) Snorkellling: Homard Grosse Tete : 80.4% Homard Rouge : 19.2% Homard Vert : 0.4% b) Trap: Homard Grosse Tete : 100%

Description: Published

Description: This journal is published by the NIOF, Egypt

Description: Lake Manzalah; the largest delta Lake in Egypt represents a dynamic system that has been undergoing continuous and pronounced changes since long times. In the last year’s this Lake faced drastic problems that retarded its environmental and fisheries development; the most serious one is the discharge of waste water. It is attempted in the present study to investigate the chemical characters of Lake Manzalah water during 2001-2002. Water temperature ranged from an average of 12.35oC in January and 29.14oC in July. Dissolved Oxygen, pH and total dissolved solids were found in ranges optimum for the living of marine and freshwater fish species. The average concentrations of nutrients lied in the following ranges: 1.24 to 4.89 μmol PO4 -3 l-1 , 5.08 to 28.73 μmol SiO4 -2 l-1 and 1.81 to 17.7 μ_mol NO3-1 l-1 The concentrations of phosphorus and nitrogen compounds were found to be relatively higher at the southern regions of the Lake near to the outlets of the drains.

Description: NIOF

Description: Published

Description: The present report reviews the spiny lobster fishery on the Mahe Plateau for the 2001/2002 fishing season. The monitoring programme, set up in 1992, was continued this season to collect more information on the spiny lobster stock in order to improve and maintain proper management of this resource around the Mahe Plateau. For the 2001/2002 lobster fishing season, a total of 40 licenses were issued namely twenty seven on Mahe, five on Praslin and eight on La Digue. Similar to previous seasons, the most frequently used lobster fishing technique was snorkelling which involved 32 fishing units, whilst only four units used the trap method and one used both snorkelling and trap. For this three-month fishing season, a total of 5.5 tonnes of spiny lobsters were estimated to have been landed compared to 10.2 tonnes in 2000-2001 fishing season. Most landings were on Mahe, which accounted for 58.44 % of the total catch (3.214 tonnes) followed by Praslin with 13.89% (0.77 tonnes). Both La Digue and Silhouette groups had landings of 0.5 tonnes each. The month of November accounted for 1.36 tonnes, while 3.37 tonnes was landed in December and 0.81 tonnes in January. A total of 350 trips were undertaken equivalent to 803 man-trips for the season with 107 trips in November, 193 trips in December and 50 trips in January. The snorkelling and trap capture methods represented 96% and 4% of the total catch respectively. The catch rates represented by catch per unit effort(CPUE) throughout the season were as follows: - 12.75 kg/trip(November) - 17.49 kg/trip (December) - 16.35 kg/trip January). The main species targeted were: Homard Grosse Tete (Panuliruspenidilatus) Homard Rouge (Panulirus longipes) Homard Vert (Panulirus versicolor). The catch composition by fishing method was as follows: a.) Snorkelling: b.)Trap: Homard Grosse Tete: 65.68% Homard Grosse Tete: 14.21% Homard Rouge: 26.83% Homard Rouge: 85.79% Homard Vert: 7.07%

Description: Published

Description: Published

Description: Industrial tuna fishing

Description: Forty oyster spat collector bags were submerged at two different sites near Mahe island fofr a period between 3.2 and 11 months. Strong currents in the south-east monsoon period resulted in a few bags lying in the sand which was detrimental to spat settlement. The mean settlement rate was calculated at 15.6 oysters per bag, however 71_310= of the bags had more than 10 oysters per bag. Considering only those bags, the settlement averaged at 27 oysters per bag. The sizes of oysters in collector bags after different soaking times, indicate that growth rate in the first few months is higher than on French Polynesia. Growth rates of oysters maintained in a cage indicated an average increase of 21.7 mm in five months, between the size of 25.9 mm and 47.76 mm. The observed mortality over the same period was 29.2_310=. Oyster spat settlement did occur all year around, indicating that spawning also occurs all through the year. Pearlculture in Seychelles is technically feasible and pearl farms will depend,for their regular supply of oysters, on collecting methods of oyster spat produced by natural stocks. Natural oyster beds are reported to be limited in Seychelles and these beds are presently exploited for the supply of the artisanal craft industry and the jewellery industry. Suitable sites for farming operations, on the granitic and on the outer coraline islands, are limited. In view of these limitations, priority has to be given to the assessment of the actual status of oyster beds and then implement neccessary of the actual measures where needed. The continuation of the Sfa training and research program regarding optimum sites, settlement rates, growth rates and other biological information will be crucial for the future development of the industry.The successful development of the pearl oyster industry in Seychelles, will largely depend on the choice of adequate management options, concerning the resource as well as the potential commercial ventures. A guideline on pearlculture development has been produced to support future initiative in this field.

Description: Published

Description: Published

Description: A report of data collected by Mozambique, Seychelles and Somalia. As a result of a workshop funded and organised by the FAO/UNDP Indo-Pacific Tuna Programme held at the Seychelles Fishing Authority from 10-24th July 1986 these data have been processed and the statistics reported.

Description: Published

Description: Fishing performances of four different types of boats (pirogues, outboard, whalers, schooners) are studied through the analysis of the temporal evolution, between July 1985 and June 1988, for four parameters: numbers of active fishing boats,- total number of fishing trips, - average number of trips/boat, - average trip duration. The trends from these analysis reveals that the boats involved in the handline fishery in seychelles have evolved considerably. These changes must be taken into consideration in the case of an eventual reorganisation of the fleet.

Description: Published

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.

Description: Published

Description: Published

Description: Published

Description: Published

Description: FISHERY DEVELOPMENT, INTERNATIONAL AGREEMENTS, FISHERY ORGANIZATIONS

Description: Published

Description: Published

Description: Contents: Preface 1. Introduction 2. Linear Regression 3. Discretizing Continuous Inverse Problems 4. Rank Deficiency and Ill-Conditioning 5. Tikhonov Regularization 6. Iterative Methods 7. Other Regularization Techniques 8. Fourier Techniques 9. Nonlinear Regression 10. Nonlinear Inverse Problems 11. Bayesian Methods Appendix A: Review of Linear Algebra Appendix B: Review of Probability and Statistics Appendix C: Glossary of Notation; Bibliography; Index It is accompanied by a Web site that contains Matlab code corresponding to all examples. Audience: Students and professionals in Astrophysics, Applied Mathematics, Atmospheric Science, Geologiocal Engineering, Geophysics, Hydrology, Oceanography and related fields.

Description: Published