Wideband multipath rejection for shallow water synthetic aperture sonar imaging

Synthetic aperture sonar (SAS) is an emerging technology for seafloor imaging, which has an appealing property of range-and frequency-independent spatial processing resolution. However, for a low-frequency SAS system operated in shallow water environments, there are often strong sea surface and bottom reflected multipath components that interfere with the desired echo signals. Based upon a small vertically displaced hydrophone array, several spatial processing algorithms have been proposed for multipath reduction. Most of these algorithms, however, are only applicable to narrowband signals, whereas wideband signals are usually used in low-to-medium-frequency SAS systems in order to achieve a high range resolution. This paper presents a steered robust Capon beamforming (SRCB) approach, and applies the approach, together with the data-independent delay-and-sum beamforming and the conventional wideband robust Capon beamforming, to wideband multipath rejection for shallow water SAS imaging. Numerical simulations of the proposed SAS processing have verified the performance improvements on output image quality over conventional processing in terms of both ghost target strength reduction and contrast enhancement.