Side scan sonar using phased arrays for high resolution imaging and wide swath bathymetry

Abstract

Abstract: The design of a new bathymetric sidescan sonar dedicated to the survey of the continental shelf is described. It uses linear phased arrays in order to perform dynamically the control of the resolution through the focusing of the beams, and beam steering to compensate for yaw and pitch. The 4m long array, working at ll2kHz, yields high resolution imaging. In addition, an interferometric doublet, with a i!h spacing, provides a wide swath bai hymetric capability. Both functions take advantage of a fast digital pulse compression process. Results of sea trials with the hull mounted system (high resolution images and topographic maps) are discussed. -- I Introduction Remote acoustic sensing of the sea floor aims at two complementary goals: imaging for target localisation, bottom classification or small relief Characterisation and sounding in order to draw charts. Two techniques are now widely used for these purposes. Multibeam echosounders are hull mounted systems that are mainly devoted to bathymetric surveys. Most implementations are based on cross shaped phased arrays with a preformed beams technique. The floor is investigated across-track of the surveying ship. The perturbative motions of the ship (i.e. roll and pitch) are compensated dynamically. The soundings are derived from the backscattered echoes by considering either the amplitude or the phase when an interferometric process is performed. Such systems can build images by taking into account the energy backscattered within each beam. Side scan sonar is a much longer established lech- nique. It was originally devoted to imaging only. Antennas point to each side of the ship track and scan, with a single beam, a long and narrow strip of the sea floor. The backscattered strength provides the informa- tion needed to build images with a much higher resolu-