Projection and mosaicking of real data gathered with a front-scan sonar system

Abstract

This paper describes methods for arranging acoustic images of the seafloor by projecting and interpolating data gathered with a novel front-scan sonar system. Two different projection methods have been devised: a simpler analytical solution and a more precise ray-tracing approach. In this paper, the ray-tracing approach will be investigated with special attention on the theoretical and practical difficulties arising out of the innovative application of a front-scan sonar system to seafloor imaging. In particular, specific strategies have been devised to minimize the number of acoustic rays necessary to provide a good matching with all the samples (differing in time and steering angle) acquired by the sonar systems. To exploit the projection results in order to obtain an image defined over a dense grid of pixels, an innovative interpolation algorithm, based on the generation of virtual beam signals (only where necessary) has been got ready. The proposed projection and interpolation methods have been tested, and comparisons have been made, using real data gathered with the front-scan sonar prototype during trials at sea. The joint application of the ray-tracing projection approach and the virtual-beams interpolation technique allows one to generate high-quality images, which can be merged to create a mosaic seafloor image. The precision and quality of the resulting mosaics confirm the high degree of effectiveness of the methods proposed in this paper to project acoustic data and interpolate single images.