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A modal/WKB inversion method for determining sound‐speed profiles in the ocean and ocean bottom

The Journal of the Acoustical Society of America 2005年第S1期84卷 S175-S175页

作者： Kevin D. Casey George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Woods Hole MA 02543 Department of Ocean Engineering Woods Hole Oceanographic Institute Woods Hole MA 02543

Two approaches to determining sound‐speed profiles in the ocean and ocean bottom using measured acoustic modal eigenvalues are examined. Both methods use measured eigenvalues and mode‐dependent assumed values of the WKB phase integral as input data and use the WKB phase integral as a starting point for relating the index of refraction to depth. Inversion method 1 is restricted to monotonic or symmetric sound‐speed profiles and requires a measurement of the sound speed at one depth to convert the index of refraction profile to a sound‐speed profile. Inversion method 2 assumes that the sound speed at the ocean surface and the minimum sound speed in the profile are known and is applicable to monotonic profiles and to general single duct sound‐speed profiles. For asymmetric profiles, inversion method 2 gives the depth difference between two points of equal sound speed in the portion of the profile having two turning points, and in the remainder of the profile it gives sound speed versus depth directly. A numerical implementation of the methods is demonstrated using idealized ocean sound‐speed profiles. The two methods are used also to determine the sediment sound‐speed profiles in two shallow water waveguide models, and inversion method 1 is used to find the sediment sound‐speed profile using data from an experiment perfomed in the Gulf of Mexico. [Work supported by ONR.]

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Using spectrometry and photography to study color underwater

Using spectrometry and photography to study color underwater

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oceanS

作者： Derya Akkaynak Eric Chan Justine J. Allen Roger T. Hanlon Joint Program in Oceanography Applied Ocean Science & Engineering Massachusetts Institute of Technology and Woods Hole Oceanographic Institution Cambridge MA USA Massachusetts Institute of Technology Cambridge MA US The Brown-MBL Graduate Biological and Environmental Sciences Providence RI USA Marine Biological Laboratory Woods Hole MA USA

Most underwater images are post-processed to look pleasing to human viewers. This often results in unrealistically saturated colors. Images taken for the purpose of studying color-sensitive topics such as marine animal coloration, must represent colors as accurately as possible and should not be arbitrarily enhanced. This first requires a transformation of colors from the camera color space to a device independent space. In this paper we present a method for transforming raw camera-RGB colors to a device independent space, optimizing this transformation for a particular underwater habitat. We have conducted an extensive study of the variation of color appearance underwater at a dive site in the Aegean Sea by taking 21 sets of spectrometry and irradiance readings with corresponding photographs of four different color standards. Spectral and photographic data were collected in the presence of natural daylight at various depths and under different weather conditions. In addition to the color charts, we have built a “habitat chart” to optimize this camera-specific transformation for a given dive site.

关键词： Image color analysis Cameras Lighting Sensitivity Humans Optical surface waves Optical sensors

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Low‐frequency diffraction from a free surface coupled to a semi‐infinite elastic surface as modeled by sea ice properties

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The Journal of the Acoustical Society of America 2005年第S1期85卷 S50-S50页

作者： Peter H. Dahl George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Department of Ocean Engineering Massachusetts Institute of Technology Cambridge MA 02139 Department of Ocean Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543

This paper discusses the solution of a low‐frequency plane wave incident upon a semi‐infinite elastic plate, such as an Arctic ice lend or free edge, using the Wiener‐Hopf method. By low‐frequency it is meant that the elastic properties of the plate are adequately described by the thin plate equation. For example, in a floating ice sheet, this translates into frequency‐ice thickness products that are ≲ 150. A key issue here is the fluid loading pertaining to sea ice and low‐frequency acoustics, which cannot be characterized by simplifying heavy or light fluid loading limits. An approximation to the exact kernel of the Wiener‐Hopf functional equation is used here, which is valid in this midrange fluid loading regime. The farfield diffracted pressure is found, which includes a fluid‐loaded, sub‐sonic (relative to the water) flexural wave in the ice plate. Comparisons are also made with the locally reacting approximation to the input impedance of an ice plate. The combined effects of the ice lead diffraction process represent loss mechanisms that contribute to the transmission loss in long‐range Arctic acoustic propagation.

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A self‐consistent theory of wave propagation and scattering through weakly inhomogeneous media

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The Journal of the Acoustical Society of America 2005年第S1期85卷 S70-S70页

作者： Dajun Tang George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Department of Ocean Engineering Massachusetts Institute of Technology Cambridge MA 02139 Department of Ocean Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543

A unified perturbation approach to wave propagation and scattering in weakly inhomogeneous media is presented. By separating the total wave field into an averaged coherent propagation part and a random scattering part, a set of coupled wave equations is found. The problem of a wave propagating in a random medium is changed to a problem of a pair of coupled waves propagating in a deterministic medium with randomly distributed sources. This method not only improves upon the conventional Born approximation for the scattered field, but also gives the attenuation behavior of the coherent propagating field related to the statistics of the random media. Examples of underwater acoustic waves in an inhomogeneous water column and an inhomogeneous bottom are given.

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An integral equation approach to range‐dependent boundary value problems in ocean acoustics

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The Journal of the Acoustical Society of America 2005年第S1期83卷 S117-S117页

作者： Peter H. Dahl George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543 Department of Ocean Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543

In ocean acoustics, the introduction of range discontinuities, for example, the water‐to‐ice canopy surface, creates a mixed boundary value problem. In this paper, an exact solution of certain mixed boundary value problems is discussed using the Wiener‐Hopf method. A key attribute of this approach is that it is not fundamentally numerical in nature and allows additional insight into the mathematical and physical structure of the acoustic field due to range discontinuities. The problem discussed here is a canonical one: A plane wave is incident upon a planar surface where the boundary condition changes from Dirichlet (free surface) to Neumann (hard). The boundary conditions addressed in this problem are highly idealized renditions of what happens, when, say, a plane wave is incident upon a water‐to‐ice canopy surface; nevertheless, important features of the diffraction process are produced here, and the solution gives considerable insight into the process. The solution of the diffracted potential is partitioned into two components: a field consisting of cylindrical waves weighted by a polar gain function, resulting from the artificial source created by the discontinuity in the boundary; and a field containing a residue contribution which restores field continuity along the line corresponding to specular reflection. Contour plots of equal pressure amplitude show how the component fields superimpose such that the boundary conditions are maintained, and how energy is redistributed across the angular spectrum in the diffraction process. The latter is related to mode coupling due to boundary changes in waveguide problems. [Work supported by ONR.]

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oceanic frontal divergence alters phytoplankton competition and distribution

arXiv

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arXiv 2022年

作者： Plummer, Abigail Freilich, Mara Benzi, Roberto Choi, Chang Jae Sudek, Lisa Worden, Alexandra Z. Toschi, Federico Mahadevan, Amala Department of Physics Harvard University CambridgeMA United States Princeton Center for Complex Materials Princeton University PrincetonNJ United States MIT-Woods Hole Oceanographic Institution Joint Program in Oceanography and Applied Ocean Science Woods HoleMA United States Scripps Institution of Oceanography University of California San Diego San DiegoCA United States Department of Physics Istituto Nazionale di Fisica Nucleare University of Rome Tor Vergata Rome Italy GEOMAR Helmholtz Centre for Ocean Research Kiel Germany University of California Santa Cruz Santa CruzCA United States Marine Biological Laboratory Woods HoleMA United States Department of Applied Physics Eindhoven University of Technology Eindhoven5600 MB Netherlands Istituto per le Applicazioni del Calcolo Consiglio Nazionale delle Ricerche Rome00185 Italy Department of Physical Oceanography Woods Hole Oceanographic Institution Woods HoleMA02543 United States

Ecological interactions among phytoplankton occur in a moving fluid environment. oceanic flows can modulate the competition and coexistence between phytoplankton populations, which in turn can affect ecosystem function and biogeochemical cycling. We explore the impact of submesoscale velocity gradients on phytoplankton ecology using observations, simulations, and theory. Observations reveal that the relative abundance of Synechoccocus oligotypes varies on 1–10 km scales at an ocean front with submesoscale velocity gradients at the same scale. Simulations in realistic flow fields demonstrate that regions of divergence in the horizontal flow field can substantially modify ecological competition and dispersal on timescales of hours to days. Regions of positive (negative) divergence provide an advantage (disadvantage) to local populations, resulting in up to ∼ 20% variation in community composition in our model. We propose that submesoscale divergence is a plausible contributor to observed taxonomic variability at oceanic fronts, and can lead to regional variability in community composition. © 2022, CC BY.

关键词： Phytoplankton

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Correction: Reverse engineering environmental metatranscriptomes clarifies best practices for eukaryotic assembly

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BMC bioinformatics 2023年第1期24卷 185页

作者： Arianna I Krinos Natalie R Cohen Michael J Follows Harriet Alexander MIT-WHOI Joint Program in Oceanography and Applied Ocean Science and Engineering Cambridge and Woods Hole MA USA. akrinos@mit.edu. Department of Biology Woods Hole Oceanographic Institution Woods Hole MA USA. akrinos@mit.edu. Department of Earth Atmospheric and Planetary Science Massachusetts Institute of Technology Cambridge MA USA. akrinos@mit.edu. Skidaway Institute of Oceanography University of Georgia Savannah GA USA. Department of Earth Atmospheric and Planetary Science Massachusetts Institute of Technology Cambridge MA USA. Department of Biology Woods Hole Oceanographic Institution Woods Hole MA USA. halexander@whoi.edu.

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Temporal and spatial variability in vessel noise on tropical coral reefs

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Proceedings of Meetings on Acoustics 2016年第1期27卷

作者： Maxwell B. Kaplan T. Aran Mooney Marc O. Lammers Eden Zang 1Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering Cambridge MA USA mkaplan@whoi.edu 2Biology Department Woods Hole Oceanographic Institution Woods Hole MA USA amooney@whoi.edu 3Hawaii Institute of Marine Biology Kaneohe HI Oceanwide Science Institute Honolulu HI USA lammers@hawaii.edu 4Oceanwide Science Institute Honolulu HI USA edenzang@***

Coral reef soundscapes are dynamic, demonstrating amplitude and spectral variability across timescales from seconds to seasons. Some of this variability can result from spatiotemporally heterogeneous patterns of human activity. To characterize this variability and the extent to which anthropogenic sound can modify the biological soundscape, seven Hawaiian reefs were equipped with acoustic recorders operating on a 10% duty cycle for 16 months. Spatially, vessel activity was acoustically detected unevenly across reefs; for example, vessels were acoustically present almost every day at a popular snorkeling reef but were rare in a protected area closed to boats, which indicates that exposure of reef fauna to vessel noise will vary by reef. Temporally, vessel activity was most likely to occur during daylight hours, which is consistent with patterns of human activity. This heterogeneity in exposure could have implications for physiology and behavior and underscores the need for long-term acoustic monitoring alongside more targeted studies investigating the potential for effects of noise on aquatic organisms.

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Quantifying air-sea gas exchange using noble gases in a coastal upwelling zone

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IOP Conference Series: Earth and Environmental science 2016年第1期35卷

作者： C C Manning R H R Stanley D P Nicholson M E Squibb Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering Woods Hole MA 02543 USA Department of Marine Chemistry and Geochemistry Woods Hole Oceanographic Institution Woods Hole MA 02543 USA Department of Chemistry Wellesley College Wellesley MA 02481 USA Center for Ocean Solutions Stanford University Stanford CA 94305 USA

The diffusive and bubble-mediated components of air-sea gas exchange can be quantified separately using time-series measurements of a suite of dissolved inert gases. We have evaluated the performance of four published air-sea gas exchange parameterizations using a five-day time-series of dissolved He, Ne, Ar, Kr, and Xe concentration in Monterey Bay, CA. We constructed a vertical model including surface air-sea gas exchange and vertical diffusion. Diffusivity was measured throughout the cruise from profiles of turbulent microstructure. We corrected the mixed layer gas concentrations for an upwelling event that occurred partway through the cruise. All tested parameterizations gave similar results for Ar, Kr, and Xe; their air-sea fluxes were dominated by diffusive gas exchange during our study. For He and Ne, which are less soluble, and therefore more sensitive to differences in the treatment of bubble-mediated exchange, the parameterizations gave widely different results with respect to the net gas exchange flux and the bubble flux. This study demonstrates the value of using a suite of inert gases, especially the lower solubility ones, to parameterize air-sea gas exchange.

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Corrigendum to “Hydrothermal vents: A previously unrecognized source of actinium-227 to the deep ocean” [Marine Chemistry, Volume 177, Part 4, December 2015]

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Marine Chemistry 2022年 240卷

作者： Lauren E. Kipp Matthew A. Charette Douglas E. Hammond Willard S. Moore Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering USA Department of Marine Chemistry and Geochemistry Woods Hole Oceanographic Institution Woods Hole MA 02543 USA Department of Geological Sciences University of Southern California Los Angeles CA 90089 USA Department of Earth and Ocean Sciences University of South Carolina Columbia SC 29208 USA

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