Squint and forward looking synthetic aperture sonar

This paper presents a new configuration of Synthetic Aperture Sonar (SAS): the squint SAS where the sonar beam is not perpendicular to the sonar track. Though worse than in the ideal case of a side looking SAS, the azimuth resolution of a squint SAS is in most cases better than the azimuth resolution of a conventional beam. This point is interesting in mine hunting because it allows, in a forward looking mode, long range classification of targets located ahead of the sonar. Experiments have been conducted in a shallow water sandy area of 15 meters depth. A 20 cm length sonar moving along an underwater rail was pointing to a target field composed of bottom spheres and cylinders. Sonar images have been recorded for both side looking and squint mode up to 40 degrees squint. Geometric shadows of targets have been generated after SAS processing in both cases. This result clearly shows that target classification for a squint SAS is possible.