Acoustic Daylight at Scripps Institution of Oceanography
DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION CANBERRA (AUSTRALIA)
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Acoustic daylight uses ambient noise in the ocean for target imaging. This technique is introduced and compared to traditional active and passive sonar. Theoretical studies of the method are summarized and the first experiment is described. An acoustic daylight imaging system, called ADONIS, is described in detail. It was constructed at Scripps Institution of Oceanography and consisted of a 130 element hydrophone array at the focal plane of a 3 m reflecting dish. The array elements were sensitive between 8-80 kHz. Amplification of the signal from each element was done in three stages and filtered into 16 frequency bins. The data was processed by a surface computer to produce two dimensional images displayed on a screen with a 25 Hz update rate. The device was deployed at a number of sites, with most measurements done in San Diego Bay. During some of these deployments ancillary equipment was used, including omnidirectional hydrophones. These are described, as well as measurements of the noise field in the vicinity of ADONIS. A series of targets were imaged, being planar, cylindrical and spherical in shape, at ranges of 15-40 m. Acoustic daylight images of these targets are presented under varying ensonification conditions. ADONIS was able to image all targets, with varying resolution and contrast between the target and background. In some cases it was able to distinguish between different target compositions through the reflected spectral content.
- Acoustic Detection and Detectors