Azimuth ambiguities in broadside and squint mode synthetic aperture sonar

Synthetic aperture sonar (SAS) mapping rates are limited by acoustic propagation speed in relation to feasible platform velocity and the desired swath coverage. Such limitations result in azimuth undersampling and the appearance of ambiguities in SAS imagery. The position, spreading and ambiguity to signal ratio (ASR) of image aliases caused by grating lobes are discussed from a geometric and a Doppler point of view. Simulation and experimentation for sidelooking SAS imaging show the variation in ASR with along track sampling, processed aperture, target range, and transmitted signal bandwidth. ASR is also shown to improve with increasing SAS squint angle considered up to 60 degrees from broadside.