In situ source level and source position estimates of biological transient signals produced by snapping shrimp in an underwater environment.

Biological transient signals produced by snapping shrimp are sensed underwater by a wide aperture array. The instantaneous range and bearing of the source position of each snap is estimated along with a source level equal to the peak-to-peak amplitude of the pressure impulse generated by the snap at a standard distance of 1 m from its point of origin. For a sample of 1000 snaps recorded in Sydney Harbour, the distribution of peak-to-peak sound pressure levels has a mean value of 187 dB (re 1 microPa) and an interquartile range of 185-189 dB (re 1 microPa). Plotting the Cartesian coordinates of the source positions of the biological transient signals over a period of time maps the two-dimensional spatial distribution of the local snapping shrimp population. The principal habitat is found to be geocoincident with a 120-m-long wharf, the closest point of which is 60 m from the middle of the receiving array. The passive ranging performance of the wide aperture array is evaluated by generating mechanical transient signals at selected positions along the wharf. Precise estimates of the relative times-of-arrival of the acoustic wavefronts lead to source range and bearing estimates with standard deviations of only 0.1 m and 0.005 degrees (respectively), in agreement with theoretical predictions.