Multipurpose acoustic networks in the integrated arctic ocean observing system

The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory

Oceanus.

v. 34, no. 2 (1991

Scientific challenges and present capabilities in underwater robotic vehicle design and navigation for oceanographic exploration under-ice.

This paper reviews the scientific motivation and challenges, development, and use of underwater robotic vehicles designed for use in ice-covered waters, with special attention paid to the navigation systems employed for under-ice deployments. Scientific needs for routine access under fixed and moving ice by underwater robotic vehicles are reviewed in the contexts of geology and geophysics, biology, sea ice and climate, ice shelves, and seafloor mapping. The challenges of under-ice vehicle design and navigation are summarized. The paper reviews all known under-ice robotic vehicles and their associated navigation systems, categorizing them by vehicle type (tethered, untethered, hybrid, and glider) and by the type of ice they were designed for (fixed glacial or sea ice and moving sea ice). © 2020 by the authors

Acoustic signal and noise changes in the Beaufort Sea Pacific Water duct under anticipated future acidification of Arctic Ocean waters

Author Posting. © Acoustical Society of America, 2017. 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 142 (2017): 1926–1933, doi:10.1121/1.5006184.It is predicted that Arctic Ocean acidity will increase during the next century as a result of carbon dioxide accumulation in the atmosphere and migration into ocean waters. This change has implications for sound transmission because low-pH seawater absorbs less sound than high-pH water. Altered pH will affect sound in the 0.3−10 kHz range if the criterion is met that absorption is the primary cause of attenuation, rather than the alternatives of loss in the ice or seabed. Recent work has exploited sound that meets the criterion, sound trapped in a Beaufort Sea duct composed of Pacific Winter Water underlying Pacific Summer Water. Arctic pH is expected to drop from 8.1 to 7.9 (approximately) over the next 30−50 yr, and effects of this chemical alteration on the intensity levels of this ducted sound, and on noise, are examined here. Sound near 900 Hz is predicted to undergo the greatest change, traveling up to 38% further. At ranges of 100−300 km, sound levels from a source in the duct may increase by 7 dB or more. Noise would also increase, but noise is ducted less efficiently, with the result that 1 kHz noise is predicted to rise approximately 0.5 dB.This work was supported by Office of Naval Research Grant N00014-16-1-2372

A Virtual Ocean framework for environmentally adaptive, embedded acoustic navigation on autonomous underwater vehicles

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 2021.Autonomous underwater vehicles (AUVs) are an increasingly capable robotic platform, with embedded acoustic sensing to facilitate navigation, communication, and collaboration. The global positioning system (GPS), ubiquitous for air- and terrestrial-based drones, cannot position a submerged AUV. Current methods for acoustic underwater navigation employ a deterministic sound speed to convert recorded travel time into range. In acoustically complex propagation environments, however, accurate navigation is predicated on how the sound speed structure affects propagation. The Arctic’s Beaufort Gyre provides an excellent case study for this relationship via the Beaufort Lens, a recently observed influx of warm Pacific water that forms a widespread yet variable sound speed lens throughout the gyre. At short ranges, the lens intensifies multipath propagation and creates a dramatic shadow zone, deteriorating acoustic communication and navigation performance. The Arctic also poses the additional operational challenge of an ice-covered, GPSdenied environment. This dissertation demonstrates a framework for a physics-based, model-aided, real-time conversion of recorded travel time into range—the first of its kind—which was essential to the successful AUV deployment and recovery in the Beaufort Sea, in March 2020. There are three nominal steps. First, we investigate the spatio-temporal variability of the Beaufort Lens. Second, we design a human-in-the-loop graphical decision-making framework to encode desired sound speed profile information into a lightweight, digital acoustic message for onboard navigation and communication. Lastly, we embed a stochastic, ray-based prediction of the group velocity as a function of extrapolated source and receiver locations. This framework is further validated by transmissions among GPS-aided modem buoys and improved upon to rival GPS accuracy and surpass GPS precision. The Arctic is one of the most sensitive regions to climate change, and as warmer surface temperatures and shrinking sea ice extent continue to deviate from historical conditions, the region will become more accessible and navigable. Underwater robotic platforms to monitor these environmental changes, along with the inevitable rise in human traffic related to trade, fishing, tourism, and military activity, are paramount to coupling national security with international climate security.Office of Naval Research (N00014-14-1-0214) — GOATS’14 Adaptive and Collaborative Exploitation of 3-Dimensional Environmental Acoustics in Distributed Undersea Networks Draper Laboratory Incorporated (SC001-0000001039) — Positioning System for Deep Ocean Navigation (POSYDON) Office of Naval Research (N00014-16-1-2129) — MURI: The Information Content of Ocean Noise: Theory and Experiment Office of Naval Research (N00014-17-1-2474) — Environmentally Adaptive Acoustic Communication and Navigation in the New Arctic Office of Naval Research (N00014-19-1-2716) — TFO: Assessing Realism and Uncertainties in Navy Decision Aids Department of Defense, Office of Naval Research — National Defense, Science, and Engineering Graduate Fellowshi

The Brazil current and intermediate Western Boundary Current flows through the Vitória-Trindade ridge

In order to contribute to the description of the flows of the Brazil Current (BC) and the Intermediate Western Boundary Current (IWBC) through the submerged seamounts of the Vitória-Trindade Ridge (VTR), this work compiles data from three oceanographic commissions that took place in 2013 and 2014, between 19 e 23°S. One of the commissions was specially designed for the study of the flows in the main passages between the CVT seamounts, and the other two were systematic oceanographic surveys conducted by the Brazilian Navy in the region. The study analyzes a total of 83 oceanographic stations and vessel-mounted ADCP measurements. A combined analysis of remote sensing data was performed on mesoscale features that were sampled during the cruises. As the latitude increased, the BC was intensified. In the region of the seamounts, BC cores were observed between the Abrolhos Bank and the Besnard Bank, between the Besnard Bank and Vitória Seamount, and to the south of the Vitória Seamount. The zone between ~ 20 and ~ 21.5 ° S was characterized as a region where the BC flow got reorganized by the continental slope. To the south of 21,5 ° S, the flow presented high intensity. The IWBC was also intensified along its trajectory towards north. The flow was divided into three paths at the seamounts region. Through the channel between the Besnard Bank and Monte Vitória, the greater volume transport was observed. The importance of SACW and AAIW in the IWBC flow was comparable between 22 and 19 °S. At 19.5 ° S it was possible to verify that the IWBC was organized as a single and intense branch. Cyclonic and anti-cyclonic eddies, which were sampled during the cruises, reached depths greater than 500m, thus influencing the circulation of the BC and IWBC in the region.Com o objetivo de contribuir para a descrição dos fluxos da Corrente do Brasil (CB) e da Corrente de Contorno Intermediária (CCI) através da Cadeia Vitória-Trindade (CVT), este trabalho compila dados de três comissões oceanográficas realizadas em 2013 e 2014 entre 19 e 23°S. Uma das comissões foi especialmente desenhada para o estudo dos fluxos nas principais passagens entre os montes da CVT e as outras duas foram levantamentos oceanográficos sistemáticos realizados pela Marinha do Brasil na região. O estudo analisa um total de 83 estações oceanográficas e dados de ADCP de casco. Uma análise conjunta de dados de sensoriamento remoto foi realizada em feições de mesoescala que foram amostradas durante os cruzeiros. A CB sofreu um processo de intensificação com o aumento da latitude. Na região dos montes submersos, núcleos da CB foram observados entre o Banco de Abrolhos e o Banco Besnard, entre o Banco Besnard e o Monte Vitória e ao sul do Monte Vitória. A zona entre ~20 e ~21,5 °S apresentou-se como uma região de reorganização da CB junto ao talude continental e ao sul de 21,5°S, o fluxo apresentou-se com grande intensidade. A CCI também foi intensificada ao longo de sua trajetória para o norte. O fluxo da corrente foi observado em três caminhos preferenciais entre os montes da CVT. No canal entre o Banco Besnard e Monte Vitória, o maior volume de transporte pôde ser observado. A importância da ACAS e AIA no fluxo da CCI foi comparável entre 19 e 22 °S. Em 19,5 °S pôde-se verificar a CCI organizada em um ramo único e intenso. Vórtices ciclônicos e anti-ciclônicos, amostrados durante os cruzeiros, atingiram profundidades superiores a 500m, influenciando assim a circulação tanto a CB como da CCI

Impacts of ocean warming on acoustic propagation over continental shelf and slope regions

Author Posting. © The Oceanography Society, 2018. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 31(2), (2018):174–181, doi:10.5670/oceanog.2018.219.Gradients of heat and salt affect the propagation of sound energy in the ocean. Anticipated changes in oceanic conditions will alter thermohaline conditions globally, thus altering sound propagation. In this context, we examine changes in shallow- water propagation. Because these waters are close to the surface, they will be the earliest to change as the atmospheric state and radiative conditions change. We compare current and possible future propagation patterns near fronts and across fronts on continental shelves. Changes in sound pathways between the deep ocean and coastal regions are also examined, including an example from the Arctic Ocean.GG was supported by the Office of Naval Research under grants N00014-16-1-3071 and N00014-16-1-2774

Oceanus.

v. 25, no. 2 (1982