High-precision acoustic localization of dolphin sonar click transmissions using a modified method of passive ranging...

When configured as a wide aperture array, only three hydrophones are required to localize dolphin sonar transmissions with unprecedented precision, even when the underwater sound scene of their natural habitat is complicated by many of them emitting echolocation "click" signals at the same time. Given the sensor position coordinates and speed of sound travel, the passive ranging by the wavefront curvature algorithm estimates the source range and bearing, using range difference measurements between signals, arriving at two adjacent pairs of widely spaced sensors. If the sensor positions are not strictly collinear, then the source range estimates are biased. This problem is overcome by modifying the input parameters to the basic passive ranging algorithm. The experimental results for the estimated source positions are found to agree with the predicted localization performance for a wide aperture array passive ranging sonar. The precision of the source bearing estimates is 0.005°, which is independent of the source range. The precision of the source range estimates degrades a hundredfold (from 2.5 cm to 2.6 m) for a tenfold increase in source range (33-318 m). A lower bound for the peak-to-peak source levels of Indo-Pacific bottlenose dolphins (Tursiops aduncus) is 183 ± 2 dB re 1 μPa for regular click pulses.