Iterative Adaptive Approach for wide-band active sonar array processing

Sector scan sonars can be used for detection and identification of man-made objects located on the sea floor. Wide-band acoustic signals are employed in this kind of sonar system to enhance range resolution. The conventional delay-and-sum beamformer (CBF) produces sonar images with high sidelobe levels and poor angular resolution. Adaptive beamforming algorithms together with spatial resampling can be applied to mitigate this problem. The algorithm “Spatial Processing: Optimized and Constrained” (SPOC), used in a recent work, is studied herein and shown to be identical to the basic form of the FOCal Underdetermined System Solver (FOCUSS) algorithm. A recently developed algorithm, the Iterative Adaptive Approach (IAA), is proposed for this sonar application and various implementation issues are discussed. Experimental results show that the IAA algorithm produces better sonar images than the CBF and Minimum Variance Distortionless Response (MVDR) algorithms in terms of sidelobe suppression and angular resolution. Compared with SPOC, IAA provides clearer acoustic highlights of the imaged object and a higher density of pixels representing the object.