Dual frequency synthetic aperture imaging sonar

The current state of the art in the United States Navy´s imaging sonar systems, in terms of resolution, consists of a dual high frequency and low frequency synthetic aperture sonar (SAS) system (HF/LFSAS). These two frequencies are used simultaneously to provide both a HF and a LF image of the bottom in a shallow water and very shallow water (SW/VSW) operating area. The theoretical resolution of the HF and LF is 7.5 and 2.5 cm respectively. The HF SAS provides no bottom penetration and images only proud targets. The LF SAS will penetrate the sea bottom for a few centimeters and provide images of buried objects. The data presented in this paper was processed off-line, but a real-time processor has been tested, generating similar images. Real-time processing of this sonar requires about three times ten to the ninth floating point operations per second (3 GFLOPS) to produce images in real-time. The sonar employs the displaced phase center (DPC) algorithm for motion compensation