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Navigating beneath the Arctic ice | MIT News

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The Arctic has a lot of activities under a vast, solitary expanse of snow and ice. Climate change has dramatically altered the ice layer that covers most of the Arctic Ocean. Areas of water that used to be covered by a solid ice pack are now covered by thin layers only 3 feet deep. Under the ice, a warm layer of water, part of the Beaufort lens, has changed the makeup of the aquatic environment.

To understand the role of this changing environment in the Arctic Ocean in global climate change, scientists need to map the ocean below the ice cover.

A team of MIT engineers and naval officers led by Professor of Mechanical and Ocean Engineering Heinrich Schmidt is trying to understand environmental changes, their impact on acoustic transmission below the surface, and these changes for vehicles passing under the ice How they affect navigation and communication. .

“Basically, what we want to understand is how does this new Arctic environment brought on by global climate change affect the use of underwater sound for communication, navigation and sensing?” Schmidt explains.

To answer this question, Schmidt traveled to the Arctic with laboratory members for the Autonomous Marine Sensing System (LAMSS), including Daniel Goodwin and Bradley Howard, who were graduate students at the MIT-Woods Hole Ocean Science Institute Joint Program.

With funding from the Office of Naval Research, the team participated in ICEX – or Ice Exercise – 2020, a three-week program organized by the US Navy, where military personnel, scientists and engineers undertake a variety of tasks. Research Projects and Missions.

A strategic waterway

The rapidly changing environment in the Arctic has a wide impact. In addition to giving researchers more information about the effects of global warming and its effects on marine mammals, thin ice could potentially open new shipping lanes and trade routes in areas that were previously inaccessible.

Perhaps most importantly for the US Navy, understanding the changed environment is also of geopolitical importance.

“If the Arctic environment is changing and we don’t understand it, it can have implications for national security,” says Goodwin.

Many years ago, Schmidt, a professor of mechanical and ocean engineering, and his colleague Arthur Baggeroyer, were the first to recognize that hot water, part of the Beaufort lens, with the composition of hot water, describes how sound traveled in water.

To successfully navigate throughout the Arctic, the US Navy and other entities in the region need to understand how these changes in sound propagation affect a vehicle’s ability to communicate and navigate through water.

General Dynamics-Mission Systems (GD-MS), and the Woods Hole Oceanographic Institution, a system of rigging sensors developed by Schmidt and his team, using an autonomous underwater vehicle (AUV), Dan McDonald and GD-MS’s De Lang, incorporated by Josiah, is scheduled to showcase a new integrated acoustic communication and navigation concept.

The framework, supported and developed by LAMSS members Supun Randeni, Ishan Bhatt, Rui Chen, and Oscar Wickz, as well as LAMSS alumni Toby Schneider of Gobyboft LLC, allows vehicles to go through water with GPS-level accuracy Will allow Employing oceanographic sensors for data collection.

“To prove that you can use this navigational concept in the Arctic, we must first make sure that we fully understand the environment we are operating in,” Goodwin says.

Understanding the environment below

After arriving at the Arctic Submarine Lab’s ice camp last spring, the research team conducted several conductivity-temperature-depth investigations to gather data about the aquatic atmosphere in the Arctic.

“Using temperature and salinity as a function of depth, we calculate the sound speed profile. It helps us understand whether the location of the AUV is good or bad for communication, ”says Howard, who was responsible for monitoring environmental changes in the water column throughout ICEX.

The way sound bends into water is known as Snell’s Law, sine-like pressure waves converge in some parts of the water column and propagate in others. Understanding prevalence estimates is important for predicting good and bad locations for AUV operations.

To map water areas with optimal acoustic properties, Howard modified the traditional signal-to-noise-ratio (SNR) known as multi-path penalty (MPP), which penalizes those regions. Is where the AUV eclipses. message. As a result, the vehicle prioritizes operations in areas with low reverb.

These data allowed the team to identify where the vehicle should be positioned in the water column for optimal communication, resulting in accurate navigation.

Howard collected data on how the effects of the water effect were shown, with Goodwin focusing on how sound is projected and reflected by the ever-changing ice on the surface.

To obtain these data, the AUV was designed with an instrument that measured vehicle speed relative to the snow above. That voice was raised by several receivers associated with the snow-clad moring.

The data on the vehicle and the receiver were used by the researchers to calculate the time at which the vehicle was at a certain time. Information on this location, along with data collected on acoustic environments in water, present a new navigational concept for vehicles traveling in the Arctic Sea.

Protect the arctic

After many failures and challenges due to the heterogeneous conditions in the Arctic, the team was able to successfully prove its navigational concept. Thanks to the team’s efforts, naval operations and future merchant vessels may be able to take advantage of the changing conditions in the Arctic to maximize navigational accuracy and improve underwater communications.

“Our work could improve the ability for the US Navy to safely and effectively operate submarines under ice for extended periods of time,” Howard says.

Howard acknowledges that in addition to changes in the physical climate, changes in the geopolitical climate continue. This only reinforces the need for better navigation in the Arctic.

He said, “The goal of the US Navy is to maintain peace and protect global trade by ensuring freedom of navigation across the world’s oceans.” “The navigational concept we proved during ICEX will serve to help the Navy in that mission.”

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