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

2021 ◽  
Author(s):  
◽  
EeShan Bhatt
Keyword(s):  
Travel Time ◽  
Sound Speed ◽  
Environmental Changes ◽  
Multipath Propagation ◽  
Autonomous Underwater Vehicles ◽  
Underwater Vehicles ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Human In The Loop ◽  
Spatio Temporal

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.

scholarly journals An improved sea ice detection algorithm using MODIS: application as a new European sea ice extent indicator

2021 ◽  
Vol 15 (6) ◽  
pp. 2803-2818
Author(s):  
Joan Antoni Parera-Portell ◽  
Raquel Ubach ◽  
Charles Gignac
Keyword(s):  
Sea Ice ◽  
Regional Scale ◽  
Ice Cover ◽  
Detection Algorithm ◽  
Temporal Variations ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Monitoring Tools ◽  
Spatio Temporal ◽  
Ice Detection

Abstract. The continued loss of sea ice in the Northern Hemisphere due to global warming poses a threat to biota and human activities, evidencing the necessity of efficient sea ice monitoring tools. Aiming at the creation of an improved sea ice extent indicator covering the European regional seas, the new IceMap500 algorithm has been developed to classify sea ice and water at a resolution of 500 m at nadir. IceMap500 features a classification strategy built upon previous MODIS sea ice extent algorithms and a new method to reclassify areas affected by resolution-breaking features inherited from the MODIS cloud mask. This approach results in an enlargement of mapped area, a reduction of potential error sources and a better delineation of the sea ice edge, while still systematically achieving accuracies above 90 %, as obtained by manual validation. Swath maps have been aggregated at a monthly scale to obtain sea ice extent with a method that is sensitive to spatio-temporal variations in the sea ice cover and that can be used as an additional error filter. The resulting dataset, covering the months of maximum and minimum sea ice extent (i.e. March and September) over 2 decades (from 2000 to 2019), demonstrates the algorithm's applicability as a monitoring tool and as an indicator, illustrating the sea ice decline at a regional scale. The European sea regions located in the Arctic, NE Atlantic and Barents seas display clear negative trends in both March (−27.98 ± 6.01 × 103 km2yr−1) and September (−16.47 ± 5.66 × 103 km2yr−1). Such trends indicate that the sea ice cover is shrinking at a rate of ∼ 9 % and ∼ 13 % per decade, respectively, even though the sea ice extent loss is comparatively ∼ 70 % greater in March.

Path Following of Underactuated Marine Underwater Vehicles in the Presence of Unknown Ocean Currents

2014 ◽  
Author(s):  
Signe Moe ◽  
Walter Caharija ◽  
Kristin Y. Pettersen ◽  
Ingrid Schjølberg
Keyword(s):  
Oil And Gas ◽  
Autonomous Underwater Vehicle ◽  
Autonomous Underwater Vehicles ◽  
Path Following ◽  
Oil And Gas Industry ◽  
Underwater Vehicle ◽  
Underwater Vehicles ◽  
Ocean Currents ◽  
The Arctic ◽  
Ocean Current

The use of autonomous marine vehicles, and especially autonomous underwater vehicles, is rapidly increasing within several fields of study. In particular, such vehicles can be applied for sea floor mapping, oceanography, environmental monitoring, inspection and maintenance of underwater structures (for instance within the oil and gas industry) and military purposes. They are also highly suitable for operations below ice-covered areas in the Arctic. However, there are still many challenges related to making such underwater vehicles autonomous. A fundamental task of an autonomous underwater vehicle vessel is to follow a general path in the presence of unknown ocean currents. There exist several results for underwater vehicles to follow a general path when no ocean currents are present [1] and to follow a geometrically simple path such as a straight line when ocean currents affect the vehicle [2, 3], but the problem of general path following in the presence of unknown ocean currents has not been solved yet. This paper presents a method to achieve this. The results are an extension of the results in [1], and introduce a virtual Serret-Frenet reference frame that is anchored in and propagates along the desired path. The closed-loop system consists of an ocean current observer, a guidance law, a controller and an update law to drive the Serret-Frenet frame along the path, and is shown to be asymptotically stable given that certain assumptions are fulfilled. This guarantees that the autonomous underwater vehicle will converge to the desired path and move along it with the desired velocity. Simulation results are presented to verify and illustrate the theoretical results.

scholarly journals Nonlinear acoustics methods in the investigations of elastic wave interactions in the ocean

2019 ◽  
Vol 127 ◽  
pp. 02017
Author(s):  
Sergei Tarasov ◽  
Petr Pivnev ◽  
Wenjian Chen ◽  
Dmitry Durov
Keyword(s):  
Autonomous Underwater Vehicles ◽  
Single Mode ◽  
Nonlinear Acoustics ◽  
Underwater Vehicles ◽  
The Arctic ◽  
Intensity Increase ◽  
Wave Interactions ◽  
Underwater Environment ◽  
Broadband Signal ◽  
Mode Excitation

Hydroacoustic parametric systems and methods of nonlinear acoustics in the investigation of the Ocean and the Arctic shelf are considered. A short description of the most promising directions of development of hydroacoustic systems with parametric radiating antennas is given. Characteristics of parametric devices are given, and the results of their applications to solve various problems of hydroacoustics are considered. We discuss new opportunities, which appear when applying parametric antennas, to illuminate underwater environment by autonomous underwater vehicles, and to ensure their navigation along the paths. The results of studies demonstrating single-mode excitation of a waveguide in a wide frequency band, of a parametric antenna, are presented. The possibility of broadband signal compression during its propagation in the result of waveguide dispersion, which leads to intensity increase, is shown. The ways of modernization and the prospective of application of the hydroacoustic means, using nonlinear acoustics methods, are discussed.

Climate change and biological oceanography of the Arctic Ocean

1995 ◽  
Vol 352 (1699) ◽  
pp. 277-286 ◽  
Keyword(s):  
Sea Ice ◽  
Environmental Changes ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Biological Oceanography ◽  
Exchange Processes ◽  
Arctic Sea ◽  
Chemical Conditions ◽  
Physical And Chemical

Polar environments are characterized by unique physical and chemical conditions for the development of life. Low temperatures and the seasonality of light create one of the most extreme habitats on Earth. The Arctic sea ice cover not only acts as an insulator for heat and energy exchange processes between ocean and atmosphere but also serves as a unique habitat for a specialized community of organisms, consisting of bacteria, algae, protozoa and metazoa. The primary production of sea ice algae may play a crucial role in the life cycle of planktonic and benthic organisms. Thus, a reduction of the sea ice extent due to environmental changes will influence the structure and processes of communities living inside the ice and pelagic realms.

scholarly journals A SPATIO-TEMPORAL FRAMEWORK FOR MODELING ACTIVE LAYER THICKNESS

2015 ◽  
Vol II-4/W2 ◽  
pp. 199-206
Author(s):  
J. Touyz ◽  
D. A. Streletskiy ◽  
F. E. Nelson ◽  
T. V. Apanasovich
Keyword(s):  
Layer Thickness ◽  
Active Layer ◽  
Environmental Changes ◽  
Predictive Accuracy ◽  
The Arctic ◽  
Active Layer Thickness ◽  
Error Statistics ◽  
Stochastic Component ◽  
Spatio Temporal ◽  
Naive Model

The Arctic is experiencing an unprecedented rate of environmental and climate change. The active layer (the uppermost layer of soil between the atmosphere and permafrost that freezes in winter and thaws in summer) is sensitive to both climatic and environmental changes, and plays an important role in the functioning, planning, and economic activities of Arctic human and natural ecosystems. This study develops a methodology for modeling and estimating spatial-temporal variations in active layer thickness (ALT) using data from several sites of the Circumpolar Active Layer Monitoring network, and demonstrates its use in spatial-temporal interpolation. The simplest model’s stochastic component exhibits no spatial or spatio-temporal dependency and is referred to as the naïve model, against which we evaluate the performance of the other models, which assume that the stochastic component exhibits either spatial or spatio-temporal dependency. The methods used to fit the models are then discussed, along with point forecasting. We compare the predicted fit of the various models at key study sites located in the North Slope of Alaska and demonstrate the advantages of space-time models through a series of error statistics such as mean squared error, mean absolute and percent deviance from observed data. We find the difference in performance between the spatio-temporal and remaining models is significant for all three error statistics. The best stochastic spatio-temporal model increases predictive accuracy, compared to the naïve model, of 33.3%, 36.2% and 32.5% on average across the three error metrics at the key sites for a one-year hold out period.

Advective pathways of nutrients and key ecological substances in the Arctic

2021 ◽  
Author(s):  
Myriel Vredenborg ◽  
Benjamin Rabe ◽  
Sinhue Torres-Valdès
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Ocean Circulation ◽  
Environmental Changes ◽  
Marine Ecosystem ◽  
Ocean Model ◽  
The Arctic ◽  
Large Set ◽  
Sea Ice Extent ◽  
Near Surface

<p>The Arctic Ocean is undergoing remarkable environmental changes due to global warming. The rise in the Arctic near-surface air temperature during the past decades is more than twice as high as the global average, a phenomenon known as the “Arctic Amplification”. As a consequence the Arctic summer sea ice extent has decreased by more than 40 % in recent decades, and moreover a year-round sea ice loss in extent and thickness was recorded. By opening up of large areas formerly covered by sea ice, the exchange of heat, moisture and momentum between the ocean and the atmosphere intensified. This resulted in changes in the ocean circulation and the water masses impacting the marine ecosystem. We investigate these changes by using a large set of hydrographic and biogeochemical data of the entire Arctic Ocean. To better quantify the current changes in the Arctic ecosystem we will compare our observational data analysis with high-resolution biogeochemical atmosphere-ice-ocean model simulations.</p>

NOAA’s National Undersea Research Program

2000 ◽  
Vol 34 (4) ◽  
pp. 61-68 ◽  
Author(s):  
Andrew N. Shepard
Keyword(s):  
Research Program ◽  
Environmental Changes ◽  
Autonomous Underwater Vehicles ◽  
Underwater Vehicles ◽  
Federal Program ◽  
Ocean Science ◽  
Oceanographic Research ◽  
And Performance ◽  
Scientific Diving

The National Oceanic and Atmospheric Ad/ministration (NOAA) works to understand ocean and Great Lakes’ environments and their resources, and develop the capability to predict environmental changes. This mission requires a comprehensive oceanographic research program, including the use of undersea technologies. The in situ undersea approach to ocean science allows acquisition of otherwise unobtainable observations, samples, and experimentation. NOAA’s National Undersea Research Program (NURP) places scientists underwater, directly through the use of submersibles, underwater laboratories, and wet diving, or indirectly using remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), and ocean observatories. Scientific diving is an integral part of NURP’s research efforts. The program seeks to safely maximize the capabilities of the nation’s scientific diving community through direct assistance from program experts, and development of new and improved technologies. NURP is also the only federal program with the legislative mandate to improve the safety and performance of divers.

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