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An MIT team has created a navigational system that autonomous vehicles can use to navigate the Arctic Ocean without GPS.
Under the Arctic’s vast expanses and lonely snow and ice, there is much activity. The Arctic Ocean’s layer of ice has been drastically altered by climate change. The thin layers of ice that once covered large water areas are now only three feet thick. The Beaufort Lens is a warm layer of water that has altered the aquatic environment.
Scientists need to map the ocean below the ice to understand how the Arctic Ocean is changing.
Henrik Schmidt (professor of mechanical and ocean engineering at MIT) leads a team of engineers and naval officers from MIT who are trying to understand the effects of environmental changes on acoustic transmission below the surface and how these changes impact navigation and vehicle communication traveling below the ice.
Schmidt explains that what Schmidt is trying to figure out is “How does the new Arctic environment caused by global climate change affect underwater sound for communication and navigation?”
The research team is preparing to deploy an autonomous underwater vehicle made by General Dynamics Mission Systems for testing their navigational concept.
Schmidt and the Laboratory for Autonomous Marine Sensing Systems members (LAMSS), Daniel Goodwin, Bradley Howard, and graduate students in the MIT Woods Hole Oceanographic Institution Joint Program traveled to the Arctic to answer that question.
The Office of Naval Research funded the team and participated in ICEX 2020. This three-week program is hosted by the U.S. Navy, where military personnel, engineers, and scientists work side-by-side on various research and mission projects.
Strategic waterway
The rapid changes in the Arctic environment have wide-ranging consequences. Researchers will have more information on the impacts of global warming and its effects on marine mammals. Thinning ice could also open new trade routes and shipping lanes in previously unreachable areas.
Understanding the altered environment is crucial for the U.S. Navy.
Goodwin says, “If the Arctic environment changes and we don’t understand it, then that could have implications for national security.”
Schmidt and Arthur Baggeroer (a professor of mechanical engineering and ocean engineering) were the first to notice that water temperature and changing ice composition impacted sound travel.
The team overcame several obstacles and setbacks in Arctic conditions to retrieve the autonomous underwater vehicle successfully.
The U.S. Navy and other agencies in the Arctic region must understand how changes in sound propagation affect vehicles’ ability to communicate and navigate through water.
Schmidt and his team used an unpiloted autonomous underwater vehicle (AUV) built by General Dynamics-Mission Systems. They also used a system with sensors rigged to the buoys that Woods Hole Oceanographic Institution created. Josiah DeLange and Dan McDonald of GD-MS joined them in demonstrating a new integrated acoustic communication, navigation, and communications concept.
This framework was also developed and supported by LAMSS members Supun Randeni, EeShan Bhhatt, Rui Chan, and Oscar Viquez. It would allow vehicles to navigate through water with GPS-level accuracy and use oceanographic sensors for data collection.
Goodwin adds, “To prove that this navigational concept can be used in the Arctic,”
Below is a description of the environment.
After arriving at the Arctic Submarine Lab’s ice camp last spring, the research team deployed several conductivity-temperature-depth probes to gather data about the aquatic environment in the Arctic.
We calculate the sound speed profile using temperature and salt as a function of depth. This allows us to understand if the AUV is located in a good or bad area for communication,” Howard says. Howard was responsible for monitoring environmental changes within the water column during ICEX.
The team consisted of Professor Henrik Schmidt and MIT-WHOI Joint Program Graduate Students Daniel Goodwin and Bradli Howard and members of the Laboratory for Autonomous Marine Sensing Systems and the Arctic Submarine Lab. They visited the Arctic as part of ICEX 2020. This three-week program is hosted at the U.S. Navy, where military personnel, scientists, and engineers collaborate on various missions and research projects.
Through a concept called Snell’s Law (sound bends in water), sine-like pressure waves accumulate in certain parts of the water column and disperse elsewhere. Knowing the propagation paths is crucial to predict the best and worst locations for the AUVs to operate.
To map the water areas with optimal acoustic properties, Howard modified the traditional signal-to-noise ratio (SNR) by using a metric known as the multi-path penalty (MPP), which penalizes areas where the AUV receives echoes of the messages. The vehicle will prioritize operations in the regions that have less reverb.
This data enabled the team to pinpoint precisely where the vehicle should be placed in the water column to ensure optimal communication, leading directly to accurate navigation.
Howard collected data about the water’s characteristics and acoustics. Goodwin focused his attention on sound projection and reflection of the changing ice.
The AUV was equipped with a device to measure the vehicle’s motion relative to the ice. Multiple receivers were attached to moorings suspended from the ice to pick up this sound.
Researchers used the data from both the vehicle and receivers to determine precisely where it was at any given moment. The location data and Howard’s data on the acoustic environment provide a new navigational system for vehicles traveling in the Arctic Sea.
Arctic protection
The team proved that their navigational system worked after overcoming many obstacles and setbacks in Arctic conditions. The team’s efforts helped naval operations and future trade vessels to make the most of the changing Arctic conditions to improve navigational accuracy and underwater communication.
Howard states that Howard’s work could help the U.S. Navy safely and effectively operate submarines below the ice for extended periods.
Howard admits that the geopolitical climate is also changing. This only increases the need to improve navigation in the Arctic.
She adds that the U.S. Navy’s goal “is to preserve peace and protect international trade by ensuring freedom in navigation throughout the world’s seas.” The Navy will benefit from the maritime concept that we demonstrated during ICEX.
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