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Conference on Lasers and Electro-Optics (CLEO)

作者： Beckett Colson Anna P. M. Michel Woods Hole Oceanographic Institution Woods Hole MA USA Massachusetts Institute of Technology Cambridge MA USA MIT-WHOI Joint Program in Oceanography/Applied Ocean Science & Engineering Cambridge and Woods Hole MA USA

The measurement of dissolved carbon dioxide is important for understanding many ocean processes. Here we present the design and field deployment of a TDLAS sensor for the measurement of dissolved carbon dioxide.

ISBN: (纸本)9781943580910

关键词： Spectroscopy Semiconductor lasers Oceans Instruments Sea measurements Measurement by laser beam Carbon dioxide

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Vertical Glider Robots for Subsea Equipment Delivery

Vertical Glider Robots for Subsea Equipment Delivery

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2011 IEEE International Conference on Robotics and Automation(2011年IEEE世界机器人与自动化大会 ICRA 2011)

作者： Brooks Reed Charles Ambler Franz Hover Julio Guerrero Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanogr Department of Mechanical Engineering at MIT CambridgeMA 02139 USA Department of Mechanical Engineering at MIT Cambridge MA 02138 USA

We have developed an underwater vehicle that offers significant performance improvements over existing subsea elevators. Our Vertical Glider Robot falls under its own weight to a precise location on the seafloor, employing streamlining, active steering, and basic navigation *** examine typical at-sea mission requirements, mention several key governing parameters, and outline our design approach. We then describe a prototype device, and present results from model-scale experiments.

关键词： Vehicles Cameras Elevators Navigation Sensors Sea measurements Marine vehicles

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Robotic Planning under Uncertainty in Spatiotemporal Environments in Expeditionary Science

arXiv

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arXiv 2022年

作者： Preston, Victoria Flaspohler, Genevieve Michel, Anna P.M. Fisher, John W. Roy, Nicholas MIT-WHOI Joint Program Massachusetts Institute of Technology CambridgeMA02139 United States Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution United States Computer Science and Artificial Intelligence Laboratory Massachusetts Institute of Technology CambridgeMA02139 United States

In the expeditionary sciences, spatiotemporally varying environments - hydrothermal plumes, algal blooms, lava flows, or animal migrations - are ubiquitous. Mobile robots are uniquely well-suited to study these dynamic, mesoscale natural environments. We formalize expeditionary science as a sequential decision-making problem, modeled using the language of partially-observable Markov decision processes (POMDPs). Solving the expeditionary science POMDP under real-world constraints requires efficient probabilistic modeling and decision-making in problems with complex dynamics and observational models. Previous work in informative path planning, adaptive sampling, and experimental design have shown compelling results, largely in static environments, using data-driven models and information-based rewards. However, these methodologies do not trivially extend to expeditionary science in spatiotemporal environments: they generally do not make use of scientific knowledge such as equations of state dynamics, they focus on information gathering as opposed to scientific task execution, and they make use of decision-making approaches that scale poorly to large, continuous problems with long planning horizons and real-time operational constraints. In this work, we discuss these and other challenges related to probabilistic modeling and decision-making in expeditionary science, and present some of our preliminary work that addresses these gaps. We ground our results in a real expeditionary science deployment of an autonomous underwater vehicle (AUV) in the deep ocean for hydrothermal vent discovery and characterization. Our concluding thoughts highlight remaining work to be done, and the challenges that merit consideration by the reinforcement learning and decision-making community. Copyright © 2022, The Authors. All rights reserved.

关键词： Decision making

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A technique for generating synthetic acoustic fields in shallow water

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The Journal of the Acoustical Society of America 2005年第S1期76卷 S11-S11页

作者： Michael S. Wengrovitz George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Woods Hole MA 02543 Woods Hole Oceanographic Institution Woods Hole MA 02543

A numerical scheme for generating both the trapped mode and continuum portions of acoustic fields for a horizontally stratified ocean and bottom is presented. The technique is based on the fact that the branch line integral corresponding to the continuum portion of the field can be performed by Hankel transforming a modified Green's function. The modified Green's function is obtained by removing the pole contributions from the actual Green's function. The continuum portion is then added to the trapped mode portion to form the total synthetic field. The technique has the advantage that it is fast, accurate, and can be used for a more general geoacoustic model than the Pekeris waveguide. Synthetic results for several examples are presented and discussed.

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Scattering off rough boundaries in ray and normal mode theory with applications to ocean acoustic tomography and shallow water acoustics

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The Journal of the Acoustical Society of America 2005年第S1期77卷 S101-S101页

作者： James F. Lynch George V. Frisk James H. Miller Woods Hole Oceanographic Institution Woods Hole MA 02543 MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Woods Hole MA 02543

Two quantities which can be important, both in acoustic tomography and in shallow water acoustics, are the spread and wander in time of received acoustic pulses due to boundary scattering. These effects limit the pulse travel time resolution one may achieve and then ultimately the resolution of features in the water column (tomography) or ocean bottom (shallow water acoustics). In order to calculate these effects, a breakup of the scattering into adiabatic (leading to pulse wander) and coupled (leading to pulse spreading) ray and mode components was made, and moments of the deterministic propagation results were generated. Applications of this work to coherent array processing and further extensions of this work will be discussed. [Work supported by ONR.]

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Estimating sea surface spectra with acoustic tomography

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The Journal of the Acoustical Society of America 2005年第S1期80卷 S82-S82页

作者： James H. Miller Ching‐Sang Chiu James F. Lynch MIT/WHOI Joint Program in Oceanographic Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543 Woods Hole Oceanographic Institution Woods Hole MA 02543

A technique for estimating space‐ and time‐varying sea surface spectra using acoustic tomography is described. The technique uses acoustic (mode and/or ray) phase or travel time perturbations as data for the inversions. The inverse problems for spatially homogeneous and spatially nonhomogeneous frequency‐directional wave spectra are discussed. Resolution and accuracy of the technique are addressed. Results of inversions of synthetic data are presented as well as an application of this technique to data taken during the MIZEX '84 preliminary tomography experiment. Directions of future research are indicated.

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

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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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Characterization of range‐dependent shallow water waveguides

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The Journal of the Acoustical Society of America 2005年第S1期80卷 S52-S52页

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

A technique for characterizing range‐dependent shallow water waveguides is described. The method consists of determining the beamformed output of a horizontal array over short apertures for signals due to a cw point source. By modeling the acoustic field locally as a sum of damped normal modes and using Prony's method to perform the beamforming, the local modal structure of the waveguide can be resolved. As a result, the modal composition of the waveguide as a function of range can be determined and interpreted in terms of range‐dependent mode theories (e.g., adiabatic mode theory). In addition to identifying important propagation characteristics such as mode cutoff, the method can be used to determine range‐dependent acoustic properties of the bottom. Examples of the application of the technique to the case of propagation in a wedge‐shaped ocean are presented. [Work supported by ONR.]

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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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Lagrangian surface signatures reveal upper-ocean vertical displacement conduits near oceanic density fronts

arXiv

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arXiv 2022年

作者： Aravind, H.M. Verma, Vicky Sarkar, Sutanu Freilich, Mara A. Mahadevan, Amala Haley, Patrick J. Lermusiaux, Pierre F.J. Allshouse, Michael R. Mechanical and Industrial Engineering Northeastern University BostonMA02115 United States Mechanical and Aerospace Engineering University of California San Diego La Jolla CA92093 United States MIT–WHOI Joint Program in Oceanography CambridgeMA02139 United States Woods Hole Oceanographic Institution Woods HoleMA02543 United States Department of Mechanical Engineering Massachusetts Institute of Technology CambridgeMA02139 United States

Vertical transport in the ocean plays a critical role in the exchange of freshwater, heat, nutrients, and other biogeochemical tracers. While there are situations where vertical fluxes are important, studying the vertical transport and displacement of material requires analysis over a finite interval of time. One such example is the subduction of fluid from the mixed layer into the pycnocline, which is known to occur near density fronts. Divergence has been used to estimate vertical velocities indicating that surface measurements, where observational data is most widely available, can be used to locate these vertical transport conduits. We evaluate the correlation between surface signatures derived from Eulerian (horizontal divergence, density gradient, and vertical velocity) and Lagrangian (dilation rate and finite time Lyapunov exponent) metrics and vertical displacement conduits. Two submesoscale resolving models of density fronts and a data-assimilative model of the western Mediterranean were analyzed. The Lagrangian surface signatures locate significantly more of the strongest displacement features and the difference in the expected displacements relative to Eulerian ones increases with the length of the time interval considered. Ensemble analysis of forecasts from the Mediterranean model demonstrates that the Lagrangian surface signatures can be used to identify regions of strongest downward vertical displacement even without knowledge of the true ocean state. © 2022, CC BY.

关键词： Surface measurement

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