A Fast Imaging Algorithm for Downward-Looking 3D Synthetic Aperture Sonars

Downward-looking three-dimensional (3D) synthetic aperture sonars (SASs) have been applied to image underwater objects, sea bottom and subbottom. Unfortunately, the computational load of the conventional imaging algorithm in downward-looking 3D SASs is high. To mitigate the high computational load, a fast imaging algorithm based on a derived near-field approximation by using the cylindrical coordinate system is proposed. The proposed fast imaging algorithm reduces the computational load by three orders of magnitude, compared to the conventional imaging algorithm. Both the simulation and experiment show that the imaging accuracy of the proposed fast imaging algorithm is comparable to that of the conventional one.