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  • 11
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    Characterization of heterogeneities in the sandy facies of the Opalinus Clay (Mont Terri underground rock laboratory, Switzerland) (2024)
    In:  Geophysical Journal International
    Details
    Publication Date: 2024-01-16
    Description: This contribution is presenting a multidisciplinary investigation of heterogeneities in a clay rock formation, based on seismic tomography, logging and core analysis, as a reconnaissance study for a diffusion experiment. Diffusion experiments in clay rock formations provide crucial experimental data on diffusive transport of radionuclides (RN) in extremely low hydraulic conductivity media. Previous diffusion experiments, conducted, for example, in the Mont Terri underground rock laboratory within the relatively homogeneous shaly facies of Opalinus Clay, and modelling studies of these experiments have demonstrated that the clay rock could sufficiently well be described as a homogeneous anisotropic medium. For other lithofacies, characterized by larger heterogeneity, such simplification may be unsuitable, and the description of heterogeneity over a range of scales will be important. The sandy facies of the Opalinus Clay exhibits a significantly more pronounced heterogeneity compared to the shaly facies, and a combined characterization and RN diffusion study has been initiated to investigate various approaches of heterogeneity characterization and subsequent diffusion in a heterogeneous environment. As an initial step, two inclined exploratory boreholes have been drilled to access the margins of the experiment location. These boreholes have been used to acquire a cross-hole tomographic seismic data set. Optical, natural gamma and backscattering logging were applied and rock cores were analysed. The integrated results of these investigations allowed the identification of an anomalous brighter layer within the investigated area of the sandy facies of approximately 1 m thickness and with its upper bound at roughly 10 m depth within the inclined exploratory wells. Mineralogical analyses revealed only slight variations throughout the rock cores and indicated that the anomalous layer exhibited a slightly higher quartz content, and locally significantly higher calcite contents, accompanied by a lower content of clay minerals. The anomalous layer was characterized by reduced natural gamma emissions, due to the lower clay content, and increased neutron backscattering likely indicating an increased porosity. Seismic P-wave velocities, derived from anisotropic tomography, exhibited a maximal gradient near the top of this layer. The transition from the overlaying darker rock matrix into this layer has been identified as an appropriate location for the setup of a tracer diffusion experiment in a heterogeneous environment.
    Type: info:eu-repo/semantics/article
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  • 12
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    On the reliability of the Matuyama–Brunhes record in the Sulmona Basin—Comment to ‘A reappraisal of the proposed rapid Matuyama–Brunhes geomagnetic reversal in the Sulmona Basin, Italy’ by Evans and Muxworthy (2018) (2019)
    In:  Evans, M.E. & Muxworthy, A.R., 2018. A re-appraisal of the proposed rapid Matuyama–Brunhes geomagnetic reversal in the Sulmona Basin, Italy, Geophys. J. Int., 213(3), 1744–1750.
    Details
    Publication Date: 2019-01-09
    Description: The Matuyama–Brunhes Boundary (MBB) recorded in the lacustrine sequence in the Sulmona basin (central Apennines, Italy) raised considerable scientific interest and has been the focus of various papers (Giaccio et al. 2013; Sagnotti et al. 2014; 2016). The interest comes from evidence for a very sharp geomagnetic polarity transition, that is radioisotopically dated. A paper recently published by Evans and Muxworthy (2018) questions the reliability of the Sulmona palaeomagnetic record. With new measurements on companion samples from the same stratigraphic block studied by Evans and Muxworthy, we show that directional results obtained by different demagnetization treatments (AF, thermal and thermal + AF) are in close agreement.We here propose a different interpretation of the magnetostratigraphy, and confirm that the palaeomagnetic record of the MBB geomagnetic reversal in the Sulmona basin is properly documented
    Description: Published
    Description: 296–301
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Keywords: Reversals: process, time scale, magnetostratigraphy ; Rock and mineral magnetism. ; 04.05. Geomagnetism ; 04.04. Geology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 13
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    The correct status of Elaps collaris Schlegel (1913)
    In:  Notes from the Leyden Museum (1872-9231) vol.35 (1913) nr.3/4 p.171
    Details
    Publication Date: 2014-11-24
    Description: In 1908 Dr. F. A. JENTINK, Director of the Natural History Museum at Leyden (Holland) and Dr. TH. W. VAN LIDTH DE JEUDE graciously extended the courtesy of allowing me to study for a few weeks in the Herpetological Department of the Leyden Museum. The type specimens of Elaps collaris which were described by SCHLEGEL in 1837 were examined. This species was correctly placed by its author in the genus Elaps. It belongs to the group that is characterized by Mr. BOULENGER as having the “symphysial in contact with the anterior chin-shields”. It is allied to E. narduccii JAN, which it resembles in having the sixth supralabial in contact with the parietal and in the colour pattern of the body. It is specifically distinct in the following details: The parietal shield is shorter, being less than the interorbital space; the nuchal band is sharply defined, and cannot be mistaken for the light band over the head, that is so common a mark in the genus; the gastrosteges are less numerous, the records are from two hundred twentyeight to two hundred twenty-nine, whereas the range in narduccii is from two hundred forty to three hundred fifteen.
    Repository Name: National Museum of Natural History, Netherlands
    Type: Article / Letter to the editor
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  • 14
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    Leaf growth of the seagrass Syringodium filiforme in outer Florida Bay, Florida (2021)
    In:  arthur@virginia.edu | http://aquaticcommons.org/id/eprint/14908 | 403 | 2014-03-11 22:34:30 | 14908 | United States National Ocean Service
    Details
    Publication Date: 2021-06-28
    Description: Leaf growth of the seagrass Syringodium filiforme (Kütz., 1860) was determined using a new technique based on the growth of emergent leaves (EL method) and compared to the more labor intensive repeated measurements (RM) and demographic allometric age reconstruction techniques (DA). All three techniques were used to compare leaf growth dynamics of plants with different morphologies at two sites, a shallow water (0.5 m) banktop and an adjacent deeper water (1.5 m) environment in outer Florida Bay, Florida. Leaf formation rates (Leaf Plastochrone Interval or PI) determined using the EL and RM methods were nearly identical, with means of 20 and 21 d leaf–1 at both sites, significantly faster than the 30 d leaf–1 calculated using the DA method. The EL method produced the highest estimate of leaf growth, 1.8 and 1.9 cm d–1 at the 0.5 m and 1.5 m sites, respectively, followed by the RM method (1.3 and 1.3 cm d–1) and the DA method (1.0 and 1.1 cm d–1). None of the methods detected differences in leaf PI, leaf growth or leaf fragmentation rates between sites. However, leaves at the 1.5 m site typically retained intact leaf tips longer than those at the 0.5 m site, and total leaf lifespan was longer at the 1.5 m site. Based on these results and the amount of field and laboratory work required by each of the methods, the new EL method is the preferred technique for monitoring leaf growth in S. filiforme.
    Keywords: Biology ; Ecology ; Management
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 571-585
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  • 15
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    Physically constrained maximum likelihood (PCML) mode filtering and its application as a pre-processing method for underwater acoustic communication (2009)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    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.
    Keywords: Underwater acoustics ; Acoustic models
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 16
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    Physically constrained maximum likelihood mode filtering (2010)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2010. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 127 (2010): 2385-2391, doi:10.1121/1.3327799.
    Description: Mode filtering is most commonly implemented using the sampled mode shapes or pseudoinverse algorithms. Buck et al. [J. Acoust. Soc. Am. 103, 1813–1824 (1998)] 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 [A. L. Kraay and A. B. Baggeroer, IEEE Trans. Signal Process. 55, 4048–4063 (2007)] 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. Shallow water simulation results are presented showing the benefit of using the PCML method in adaptive mode filtering.
    Description: This work was supported by the Office of Naval Research through ONR Grant Nos. N00014-05-10085 and N00014-06-10788 and through the WHOI Academic Programs Office.
    Keywords: Acoustic noise ; Acoustic signal processing ; Adaptive filters ; Array signal processing ; Maximum likelihood estimation ; Underwater acoustic propagation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 17
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    Sub-tropical seagrass ecosystem metabolism measured by eddy covariance (2015)
    Inter-Research
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2015. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 529 (2015): 75-90, doi:10.3354/meps11314.
    Description: The metabolism of seagrass ecosystems was examined at 4 sites in south Florida, USA, using the eddy covariance technique under in situ conditions. Three sites were located across a phosphorus-driven productivity gradient to examine the combined effects of dynamic variables (irradiance, flow velocity) and state variables (sediment phosphorus and organic content, seagrass biomass) on ecosystem metabolism and trophic status. Gross primary production and respiration rates varied significantly across Florida Bay in the summer of 2012 with the lowest rates (64 and –53 mmol O2 m–2 d–1, respectively) in low-phosphorus sediments in the northeast and the highest (287 and –212 mmol O2 m–2 d–1, respectively) in the southwest where sediment phosphorus, organic matter, and seagrass biomass are higher. Seagrass ecosystems offshore of the Florida Keys had similar large daily production and respiration rates (397 and –17 mmol O2 m–2 d–1, respectively) and were influenced by flow through the permeable offshore sediments. Across all sites, net ecosystem metabolism rates indicated that the seagrass ecosystems were autotrophic in the summertime. Substantial day-to-day variability in metabolic rates was found due to variations in irradiance and flow velocity. At all sites the relationship between photosynthesis and irradiance was linear and did not show any sign of saturation over the entire irradiance range (up to 1400 µmol photons m–2 s–1). This was likely due to the efficient use of light by the large photosynthetic surface area of the seagrass canopy, an effect which can only be examined by in situ measurements that integrate across all autotrophs in the seagrass ecosystem.
    Description: This study received financial support from the Jones Environmental and Barley Scholars Program at the University of Virginia and the National Science Foundation (Chemical Oceanography grant OCE- 0536431).
    Keywords: Seagrass ; Eddy covariance ; Metabolism ; Carbon cycling
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 18
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    Modal processing for acoustic communications in shallow water experiment (2008)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2008. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 124 (2008): EL177-EL181, doi:10.1121/1.2960954.
    Description: Acoustical array data from the Shallow Water Acoustics experiment was processed to show the feasibility of broadband mode decomposition as a preprocessing method to reduce the effective channel delay spread and concentrate received signal energy in a small number of independent channels. The data were collected by a vertical array designed at the Woods Hole Oceanographic Institution. Phase-shift Keying (PSK) m-sequence modulated signals with different carrier frequencies were transmitted at a distance 19.2 km from the array. Even during a strong internal waves activity a low bit error rate was achieved.
    Description: The research was supported by ONR.
    Keywords: Acoustic arrays ; Acoustic signal processing ; Array signal processing ; Modulation ; Underwater acoustic communication
    Repository Name: Woods Hole Open Access Server
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  • 19
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    Investigation of mode filtering as a preprocessing method for shallow-water acoustic communications (2011)
    IEEE
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © IEEE, 2010. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 35 (2010): 744-755, doi:10.1109/JOE.2010.2045444.
    Description: Acoustical array data from the 2006 Shallow Water Experiment (SW06) was analyzed to show the feasibility of broadband mode decomposition as a preprocessing method to reduce the effective channel delay spread and concentrate received signal energy in a small number of independent channels. The data were collected by a vertical array, which spans the water column from 12-m depth to the bottom in shallow water 80 m in depth. Binary-sequence data were used to phase-shift-keyed (PSK) modulate signals with different carrier frequencies. No error correction coding was used. The received signals were processed by a system that does not use training or pilot signals. Signals received both during periods of ordinary internal wave activity and during a period with unusually strong internal wave solitons were processed and analyzed. Different broadband mode-filtering methods were analyzed and tested. Broadband mode filtering decomposed the received signal into a number of independent signals with a reduced delay spread. The analysis of signals from the output of mode filters shows that even a simple demodulator can achieve a low bit error rate (BER) at a distance 19.2 km.
    Description: This work was supported by the U.S. Office of Naval Research (ONR).
    Keywords: Signal processing ; Underwater acoustic arrays ; Underwater acoustic communications
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 20
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    The correct status of Elaps collaris Schlegel (1913)
    In:  Notes from the Leyden Museum vol. 35 no. 3/4, pp. 171-175
    Details
    Publication Date: 2024-01-12
    Description: In 1908 Dr. F. A. JENTINK, Director of the Natural History Museum at Leyden (Holland) and Dr. TH. W. VAN LIDTH DE JEUDE graciously extended the courtesy of allowing me to study for a few weeks in the Herpetological Department of the Leyden Museum.\nThe type specimens of Elaps collaris which were described by SCHLEGEL in 1837 were examined. This species was correctly placed by its author in the genus Elaps. It belongs to the group that is characterized by Mr. BOULENGER as having the \xe2\x80\x9csymphysial in contact with the anterior chin-shields\xe2\x80\x9d. It is allied to E. narduccii JAN, which it resembles in having the sixth supralabial in contact with the parietal and in the colour pattern of the body. It is specifically distinct in the following details: The parietal shield is shorter, being less than the interorbital space; the nuchal band is sharply defined, and cannot be mistaken for the light band over the head, that is so common a mark in the genus; the gastrosteges are less numerous, the records are from two hundred twentyeight to two hundred twenty-nine, whereas the range in narduccii is from two hundred forty to three hundred fifteen.
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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