An analytical correlation and comparison of high resolution side-scan sonar imagery and multi-beam bathymetry

Deep towed side-scan sonar vehicles acquire high quality imagery of the seafloor morphology with very high spatial resolution but poor overall locational accuracy. Correlation and comparison of the side-scan sonar data (TOBI) with bathymetry data is highly desirable to enhance seafloor modelling, and to derive further geological interpretations which were previously hidden or confused. It also improves data confidence and aid the data processing in areas such as slant-range correction and texture analysis. However the main obstacle is positional registration of the two datasets. Hydrosweep bathymetry has relatively accurate satellite positioning (via GPS) though its spatial resolution is significantly less than TOBI imagery. The usual method for satellite registration requires picking of ground controls points, on features such as road junctions, large buildings and held corners. These features are not present on the seafloor and thus a different method is required. A two stage process is suggested firstly taking an edge detector over both datasets and secondly using Chamfer matching to find the best fit of the edges. The method is fully automatic and quick. Once registration is complete, comparison of the data is possible and processing improved. For example slant-range correction can now be improved, and normalisation (removal of topographic bias) on the side-scan imagery has been attempted.