Acousto-optic localization using a dynamic, spatio-temporal array

A remote, aerial, acousto-optic sensing method has been devised to detect underwater sound from the air - breaching the air-water boundary. An acousto-optic sensor detects underwater acoustic signals by probing the water surface with a laser Doppler vibrometer (LDV) thereby achieving acoustic to optical signal conversion. The small optical reflections from the air-water interface can be used to measure the pressure field in the water. Acoustic pressure waves propagating within the water environment will cause vibrations on an air-water interface, which can be optically detected by observing the amplitude or phase characteristics of the optical beam when directed upon a vibrating surface. The acousto-optic sensor detection on a dynamic water surface relies on obtaining a representation of a signal transmitted by a sound source located underwater. A glint tracking system is utilized to obtain signal portions of interest at various spatial locations on the water surface. This is equivalent to having a single sensor at the water surface moving at a moderately high speed with near instantaneous discrete jumps in position being possible. The use of novel beamforming methods is required to provide signal reconstruction. A nontraditional, adaptive algorithm to process spatio-temporal, sparse array data for use with a laser-based sonar concept is presented with simulation results and discussed for localizing and continuously tracking an in-water sound source.