Automated two-dimensional localization of underwater acoustic transient impulses using vector sensor image processing Free

An algorithm is presented for automatically localizing transient impulsive sounds collected on several autonomous underwater vector sensors, spaced 15 to 23 m apart. The procedure, which does not require precise time synchronization, exploits transient signals of interest arriving from different azimuthal directions on each sensor. For each sensor the method first constructs time-frequency representations of both the squared acoustic pressure (spectrogram) and dominant directionality of the active intensity (azigram). Within each azigram sets of time-frequency cells associated with transient energy arriving from a consistent azimuthal sector are identified. Standard image processing techniques then link sets that share similar duration and bandwidth between different sensors, after which the algorithm triangulates the source location using the azimuths associated with the detection set. Data collected from shallow coral reef environments demonstrate the algorithm's ability to detect SCUBA bubble plumes and humpback whale song, and reveal consistent spatial distributions of somniferous fish activity. Analytical estimates and direct evaluations both yield false transient localization rates of 3%–6% in the coral reef environment. Many localized pulses have low signal-to-noise ratios, whose distribution has a median of 7.7 dB and an IQR of 7.1 dB. [Work sponsored by DARPA PALS.]