ASA 125th Meeting Ottawa 1993 May

3aUW9. Acoustic daylight: Design and performance of a multi-beam imaging system.

John R. Potter

Michael J. Buckingham

MPL 0238, Scripps Inst. of Oceanogr., University of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0238

A multibeam ``Acoustic Daylight'' [Buckingham et al., Nature 356 (1992)] system is being developed that is capable of forming real-time images at 30-Hz frame rate with 127 simultaneous beams. Objects at 10- to 200-m range will be imaged, primarily employing acoustic information over 8--70 kHz. The raw data rate of such a system is over 25 Mbyte/s, which poses serious beamforming, real-time imaging, and data storage problems. The solutions we have developed include: an acoustic lens in the form of a spherical reflector with multi-element sensor (which achieves beamforming geometrically rather than through phasing); frequency-estimator preprocessing; and an economic 40 MFlop DSP engine. The color and intensity of each pixel of the final image will be determined by the spectral shading and intensity of the received signal in each beam. The limitations of the design are explored in terms of their impact on expected performance. Image simulations have been computed based on a numerical sum of a closed-analytic expression for acoustic energy scattering from a submerged body. The illuminating noise field is chosen to represent a shallow-water waveguide. Several objects are chosen for image synthesis, corresponding to obvious applications of interest. [Work supported by the Office of Naval Research.]