A new system that tracks boat traffic on the Hudson River between New York and New Jersey by listening to the noise it produces is now under development from the Department of Homeland Security.
After all monitoring the daily ship traffic on the Hudson isn’t easy. While the bigger ships must carry an Automatic Identification System that broadcasts information about their identity and location, boats weighing less than 300 tons are often an invisible security risk.[private]
As part of research conducted in the Center for Secure and Resilient Maritime Commerce (CSR), the national DHS Center of Excellence for Marine, Island and Port Security, Alexander Sutin and a team of acoustics experts at Stevens Institute of Technology in New Jersey placed several underwater microphones (“hydrophones”) in the Hudson. These microphones recorded the din of engine and propeller noise produced by the ships above. They developed a computer algorithm that isolated each individual boat’s sound and tracked its location based on how long the sound took to travel to each microphone.
The group was also able to classify each ship based on signature characteristics in its noise. Video cameras at the surface confirmed the accuracy of their technique.
“Classification parameters can be used like fingerprints to identify what class a ship is,” Sutin said.
The propellers of slow-moving boats like barges, for example, generate low-frequency modulation, while fast-moving speedboats produce high-frequency modulation. The team used special analysis techniques for extracting high-frequency modulation using low frequencies.
The team hopes to develop a database that keeps track of every individual ship’s identity to assist various agencies, including the U.S. Coast Guard, with their missions.[/private]