MIT Underwater Backscatter Localization is like GPS for the ocean

Tracking drones or whales under the ocean is very difficult because GPS signals break down rapidly in seawater. Typically tracking objects underwater is done using acoustic signaling, but tracking devices using that technique typically require batteries, making them short-lived. MIT has a new solution that might make it easier to conduct ocean explorations and track sea creatures dubbed Underwater Backscatter Localization or UBL.

UBL doesn’t emit its acoustic signals. Rather it reflects modulated signals from its environment. That technique can give researchers positioning information at net-zero energy. MIT researchers say that the technology is still in development, but UBL could offer a key tool for Marine conservationists, climate scientists, and the U.S. Navy.

The big drawback to acoustic signaling is that generating the sound needed for it to work consumes considerable amounts of power. Devices used for acoustic signaling drain batteries very quickly, making it difficult to track objects or animals for extended periods. Changing batteries on sensors connected to whales, for instance, is extremely difficult. UBL could solve those problems in the future.

The materials used in the UBL sensors generate their own electrical charge in response to mechanical stress. When vibrating sound waves ping the sensors, piezoelectric sensors aboard the UBL devices can use that charge to selectively reflect some sound waves back into their environment. Receivers translate the sequence of reflections, known as backscatter, into a pattern of one’s for sound waves reflected and zeros for soundwaves not reflected.

That binary code can deliver information about ocean temperature or salinity. In theory, the same principle could provide location information by emitting sound waves and then checking how long it takes for the soundwave to reflect off the piezoelectric sensor and return to the observation unit. The elapsed time could be used to calculate the distance between the observer and the piezoelectric sensor.

There are challenges to UBL MIT is currently working on. One challenge is that soundwaves don’t travel directly between the observation unit and sensor. They can also move between the surface and the seabed returning to the unit at different times. To address that challenge, the researchers use frequency hopping to send signals across a range of frequencies. The devices can also modify the bitrate used depending on the ocean’s depth for ideal performance.

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