MIT Team Develops Underwater GPS to Map Ocean Floors

The team presented its research in a paper at the Association of Computing Machinery's Hot Topics in Networks workshop.

SEE ALSO: A NEW MASSIVE UNDERWATER SPACE STATION IS IN THE MAKING

Water and GPS

Once radio waves enter water they become scattered, rendering any GPS useless. This is why sonar is widely used underwater, however, this method of using acoustics is very energy-intensive. 

So, MIT researchers set themselves the task of finding a way of minimizing the use of batteries to power underwater navigation systems, and they came up with the UBL. This system is especially useful for smaller devices, such as those that follow animals underwater. 

The team looked into piezoelectric materials, these materials generate an electric charge under mechanical stress, which includes being subjected to sound waves. For their system, the researchers used piezoelectric sensors to selectively reflect back sound waves from the environment as backscatter, all while using the sound waves themselves for power. 

These sound waves were picked up by a receiver as a binary pattern with 1 standing for reflected sound waves, and 0 for unreflected ones. 

This binary signal is then used by the UBL system to carry information that could be used to create a location fix simply by timing the length of time a sound wave takes to reflect off the sensor and come back to the observation unit. 

The team has demonstrated how tricky this system is, especially in shallow waters where rebounding signals off of the ocean's floor create a complex pattern. So, the researchers turned to frequency hopping. This means that signals of varying frequencies are sent across in a pattern, returning at different times. 

Using both the timing and the phase data allowed for a more specific location fix. 

Currently, the team has a proof-of-concept UBL system that can go up to distances of 20 inches (50 cm). The team's next steps include increasing this range, and ultimately, creating a navigation system that allows autonomous vehicles to map out the ocean's floor.