Image projection and composition with a front-scan sonar system: methods and experimental results

• Published in: IEEE journal of oceanic engineering 2003-10, Vol.28 (4), p.687-698
• Main Authors: Trucco, A., Palmese, M., Repetto, S.
• Format: Article
• Language: English
• Subjects: Acoustic imaging; Acoustics; Image analysis; Image motion analysis; Information analysis; Interpolation; Marine; Marine vehicles; Mathematical analysis; Mathematical models; Motion analysis; Projection; Ray tracing; Sea beds; Sea floor; Ships; Sonar; Studies
• ISSN: 0364-9059; 1558-1691
• DOI: 10.1109/JOE.2003.819316

This paper describes a complete set of methods for arranging acoustic images of the sea floor by projecting and interpolating data gathered with a novel front-scan sonar system, developed in the context of the EC-COSMOS project. Traditional sonar imaging systems for sea-floor analysis generate acoustic images during the motion of a ship; on the contrary, the front-scan sonar system not only provides information unreachable by traditional devices (blind region), but also does not need the ship motion to compose a whole image of the sea floor. Two different projection methods have been devised: a simpler analytical solution and a more precise ray-tracing approach. The development of an analytical solution is possible under the classical assumptions about a flat sea floor and a constant sound velocity profile; when these hypotheses are not realistic or a more precise image is required, a numerical solution obtained by a ray-tracing approach can be applied, which is based on some ad hoc solutions worked out for the front-scan sonar system. To move from the projection results to an image defined over a dense matrix of pixels, an interpolation stage is needed. To this end, an algorithm based on the generation of virtual-beam signals (only where necessary) has been tested and compared with more-traditional techniques. The potentials of the proposed projection and interpolation methods have been evaluated and some comparisons have been made, using real data gathered with the COSMOS sonar prototype during trials at sea.