In-situ acoustic received level measurements with glider based reactive behaviour

Buoyancy-driven underwater gliders are typically employed to sample the water column environment in the ocean [1]. As one of the efforts of extending the capabilities of traditional underwater gliders, CMRE has been working on the ability of gliders to react to signals of interest. This capability was implemented in a Teledyne Webb Research SLOCUM glider [2], and performed via acoustic signals. During the MED-REP14 sea trial, conducted in June 2014 offshore the west coast of Sardinia (Italy), a hydrophone equipped SLOCUM glider was programmed to react to a signal simulating the line spectrum features of ship radiated noise. Upon the signal of interest being detected, the glider was scheduled to dive to a pre-determined depth and then measure continuously the acoustic received level as a function of depth and range while it was surfacing. At the sea surface, the acoustic received level data were transmitted back to the control center through the satellite, along with depth, navigation and conductivity - temperature - salinity data. This reactive behaviour was successfully demonstrated to a distance of up to 11.5 km from the acoustic source. The competence developed in this work will advance the technologies for underwater Intelligence, Surveillance and Reconnaissance missions.