EFFECT OF MULTIPATH ON SYNTHETIC APERTURE SONAR

The performance of real or synthetic aperture sonar (SAS) in shallow waters is degraded by multipath, which leads to ghost targets and reduced image contrast. This loss of image contrast fills in acoustic shadows and is therefore an important limitation for high resolution SAS applications such as minehunting, where target recognition exploits the shape and size of the shadow in addition to the echo structure. Experimental data from a 100 kHz sonar array mounted vertically on a tower in 20 m water depth show the importance of second order multipath. A specific SAS design with optimized transmit and receive beam characteristics in elevation is therefore required to achieve high SNR at large range to waterdepth ratios.