A forward-scan sonar system for small unmanned submersibles

Abstract

Over the past 3 years, work has been devoted to the development of a forward-looking sonar system that can be used in small unmanned submersibles. One of the sonar systems developed, a forward scan (FS) sonar, generates side-scan-type images with the exception that multiple scan lines (120 lines in a ±60-deg forward-looking sector) are simultaneously formed, using digital processing of the signals received by the 64 elements of the receiver hydrophone array. The system operates at 230 kHz with a 10% bandwidth using a frequency chirp. The signals received by each element of the receiver hydrophone are sampled and digitized. Since the signals only have 10% bandwidth, the digital data are filtered and decimated to reduce the volume of data processed. Test tank and at-sea sonar images have been obtained using the FS sonar at the rate of one image per second using two skybolt quad i860 processors. The target is to generate four images per second. [Work sponsored by ONR.]