Acoustic optic hybrid (AOH) sensor

The ability of laser vibrometers to receive and process acoustic echoes fro m the water surface above a submerged target is established and evaluated. Sonar echoes from a submerged target are collected from the water surface b y a laser vibrometer. Feasibility of this approach to sensing underwater so und is demonstrated. If the acoustic excitation at an otherwise undisturbed water surface is 195 to 168 dB re: 1 mu Pa, signal-to-noise ratio (SNR), a t the vibrometer output, is shown to range from about 46 to 6 dB. Capillary waves and gravity waves at the water surface are expected and shown to hav e some destructive effect on the process of echo retrieval. A series of exp eriments to quantify the surface wave effects is described. The wave experi ment results are reported. A successful attempt to acquire echoes from a su bmerged target over a grid of points for further processing into a three-di mensional image is made and described. The data acquisition and beamforming techniques constitute a three-dimensional, acoustic optic, synthetic apert ure sonar (SAS). Beamformed images are included. For an aircraft towing aco ustic sensors through the water with a mechanical link, this technique hold s the promise of increased safety and improved fuel efficiency. [S0001-4966 (00)05906-3].