ACCURACY OF THE SPATIAL REPRESENTATION OF THE SEA-FLOOR WITH BATHYMETRIC SIDESCAN SONARS

When isobath maps of the seafloor are constructed with a bathymetric s idescan sonar system the position of each sounding is derived from est imates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowled ge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the son ar and the seafloor. The relative importance of these factors in the e stimation of target location is assesed. The effects of the platform m otions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncer tainties in the elevation angle measurements are analyzed in detail. T he variances associated with the representation (orientation and depth ) of a plane, rectangular patch of the seafloor are evaluated, dependi ng on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation an gle, mostly due to the acoustic noise, is found to bring the main erro r contribution in across-track slope estimates. It can also be critica l for along-track slope estimates, overshadowing error contributions d ue to the platform's attitude. Numerical examples are presented.