Low-frequency passive acoustic surveillance with directional sensors
The problem of underwater, long-term acoustic monitoring of a defined sea area has an important role in many civilian and defence applications. The concept of passive acoustic survey using a small volumetric array on board a mobile platform has been proven at CMRE since 2012 by using compact acoustic antennas installed on mobile unmanned vehicles, such as buoyancy gliders and wavegliders. Using gliders may provide covertness, quietness, persistence, wide area coverage, real-time, continuous monitoring aimed at detection and tracking of noise sources. The present activity extends the previous work by integrating in a Slocum glider, for the first time at CMRE, an acoustic vector sensor, namely the 3D GeoSpectrum M20-040. This sensor is able to provide directionality in the band from few Hz to 3 kHz, despite its limited size. The glider has been equipped also with an acoustic modem, able to communicate with a USBL deployed from a mother ship or a gateway. Through the USBL, a Control Station can get R/T measurements of the glider position and receive its detection alarms during the underwater missions, without need of surfacing.