Bathymetric sidescan sonar : a system dedicated to rapid environment assessment

The simultaneous acquisition of seabed backscattering and bathy-morphology can be achieved either by multibeam echo sounder or by bathymetric sidescan sonar. For rapid environment assessment (REA) prior to conduct mine counter measure operations, the sonar image, representing the seabed backscattering, is the primary source of information and the bathy-morphology the secondary one. Giving preference to the acquisition of the sonar image leads to operate at shallow grazing angle with high resolution imaging systems. Hence, the bathymetric sidescan sonar is well suited to complete the primary task of high resolution seabed imaging and the secondary task of acquiring simultaneously the bathy-morphology. Based on a commercial system, GESMA has developed a high resolution bathymetric sidescan sonar. After a description of the system and the array processing techniques which provides simultaneously the high resolution image and the bathy-morphology, the paper presents the experimental results from several sea trials conducted in various environments (Iroise sea-FR, Lyon gulf-FR, La Corona-SP, Ligurian Sea-IT, Victoria Harbor-CA). The analysis of these results demonstrates the potential and the limitations of the bathymetric sidescan sonar.