A Self Contained Recorder For Acoustic Observations from AUV´s

An experiment to acoustically observe baleen whale vocalizations from autonomous underwater vehicles (AUV´s) in the southwestern Gulf of Maine was conducted in May of 2005. A digital recorder and hydrophone were installed on three Slocum Electric Gliders, which have the desirable features of a low acoustic signature and the ability to persistently keep station. To adequately identify whale vocalizations, the recorders combined fidelity (a combination of sampling frequency and bit depth) and unit-to-unit clock accuracy, for determining source location by using time of arrival triangulation. A fourth glider was configured with an ADCP. All four gliders were also outfitted with conductivity, temperature, depth, and bio-optical sensors. They were programmed to keep station 5-7 km apart in an approximate equilateral formation. The recorders were installed internally with a bottom-mounted hydrodynamic-shaped hydrophone. The electronics were electrically isolated from the glider and designed to be started and stopped in response to the passage of a magnet near a section of the hull. Each recorder, powered by a 10 ´C´ cell battery pack and using a 4 GB compact FLASH card, can thus store a single channel linear encoded 16-bit audio signal, sampled at 2048 Hz for 12 days. A module was designed and built to synchronize the ultra stable temperature tracking real time clocks. By using spectrogram cross correlation of the acoustic data, and estimates of the glider location, whale positions were determined with an accuracy of a few hundred meters