New Acoustic Research Makes it Harder for Drone Subs to Hide

A team of researchers from defense contractor Draper, MIT and the Woods Hole Oceanographic Institute (WHOI) have developed a new way to track unmanned underwater vehicles at long range.

Detection, classification and tracking are important for port security and the security of coastal and offshore operations, says Kristen Railey, a PhD candidate at MIT and the lead author of the paper. “However, identifying UUV signatures and using those signatures to estimate a UUV’s speed for passive tracking is a relatively unexplored research area in comparison to other marine vessels," she said. 

Detecting an unmanned underwater vehicle (UUV) is normally done by picking up and characterizing the noise created by its propeller. In a busy harbor, this task is difficult because the background noise is often too complex for current methods to filter out. The standard approach is to apply a specialized processing technique called Detection of Envelope Modulation on Noise (DEMON). However, this method varies by vessel and does not always work well in shallow or congested harbor environments. 

The authors focused their study on micro-UUVs, which are less than six inches in diameter. Focusing on the high frequency acoustic signature of the brushless DC motors commonly used in these devices, the team designed a new method for determining a mico-UUV's propeller rotation frequency. In testing, they found that their method could pick up and distinguish this acoustic signature even when larger and louder boats were passing by - something that the DEMON method could not do. 

“Understanding the origins of acoustic noise in autonomous platforms can inform quieter UUV propulsion design to avoid interference with onboard sensors and disturbance to marine life. In the future, based on these findings, quieting techniques for [brushless DC] motors in UUVs can be compared and assessed," the authors wrote. 

Their paper is focused on micro-UUVs, but Draper says that the new method could also apply to other devices powered by mass-manufactured brushless DC motors. These motors aren't just found on electric watercraft - they are essential to electric vehicles, hybrid vehicles, electric aircraft and electric mobility devices.