Abstract:

A synthetic aperture sonar (SAS) system has been developed by Dynamics Technology, Inc. (processing lead), and Hughes Aircraft Naval and Maritime Systems (hardware and operation). The system operates at 50 kHz and features a 3.2-m-long, 16-element linear array and a data acquisition system that records phase and amplitude information for each element. Towbody motion is estimated from information contained in the sonar data through the use of a type of long-track interferometry, aided by data from a simple motion compensation suite consisting of Doppler sonar and a single gyro. This combination compensates motion to levels correctable by standard SAR autofocus techniques modified for SAS. The system has demonstrated, at long ranges (up to 1000 m), high-resolution images (better than 20 cm), previously achievable only with high-frequency sonars at close range. The low-carrier frequency allows high-resolution imaging of the interior structures of submerged objects, recently demonstrated by SAS imagery revealing the rib and spar structure inside a wrecked PB4Y-2 airplane in Lake Washington. [Work supported by DARPA.]