On-board underwater glider real-time acoustic environment sensing

Underwater gliders are autonomous vehicles that use small changes in their buoyancy in conjunction with wings to convert vertical motion to horizontal, and thereby propel themselves forward, with very low power consumption, through the ocean for a long period of time. Gliders typically make measurements such as temperature, conductivity (to calculate salinity), currents, chlorophyll fluorescence, optical backscatter and bottom depth. However, such a platform could be a good candidate if properly equipped with an acoustic payload to persistently monitor the underwater acoustic environment. For that reason, NURC and the Technical University of Catalonia (UPC) decided in 2010 to jointly develop a glider acoustic payload that would provide the recording of two hydrophones but also, which is quite unique, provide in addition a real-time detection / classification (DC) capability. The DC capability will allow, while the glider being at-sea, to provide real-time feedback on the acoustic environment the glider is passing by, instead of only providing recording capability for postprocessing work as previously done in the past. The purpose of the paper is to describe the characteristics of the system that has been developed and additionally reports at-sea results from a deep-water WEBB glider operating in the Mediterranean Sea. Those results demonstrate the capability of the developed acoustic payload to detect and classify marine mammals in real-time within the glider. Examples of the noise generated by the glider are also presented.