Sonar Detection Of Small Objects On Rough Seafloor

Abstract

A computer model, which previously has been used to simulate the performance of multibeam echo-sounding systems, is applied here to analyses of the echolocation of small objects situated on rough seafloor. The model accounts for sounding system parameters (e.g., source waveform, pulse duration, and beam- width), platform track a,nd speed, refraction and spherical spreading in the water column, and backscattering from a fully three-dimensional bottom. The sounding beam is modeled as a set of rays which span the beam. By increasing the density of rays within the beam, arbitrary reso- lution can be obtained. The calculations produce a set of travel times and scattered intensities describing the purely acoustical response of the system. The acoustical response is subsequently postprocessed using a standard algorithm for bottom detection enhancement. The bottom de- scription consists of measured bathymetry from a rough, mid-oceanic ridge province. The detec- tion of a small object by means of travel-time measurements is quantified as a function of beamwidth. A cube, one meter on a side and resting upon the bottom at a depth of 200 m, cannot be detected when the sounding system beamwidth is 20 or greater. The detection of a buried object by means of intensity measure- ments is also examined. The same cube, now buried just below the bottom at the same depth, can be detected as long as the impedance con- trast with the surrounding material is suffi- ciently large.