GEOMETRIC CORRECTIONS ON SIDESCAN SONAR IMAGES BASED ON BATHYMETRY - APPLICATION WITH SEAMARC-II AND SEA BEAM DATA

Acoustic backscatter images of the seafloor obtained with sidescan son ar systems are displayed most often using a flat bottom assumption. Wh enever this assumption is not valid, pixels are mapped incorrectly in the image frame, yielding distorted representations of the seafloor. H ere, such distortions are corrected by using an appropriate representa tion of the relief, as measured by the sonar that collected the acoust ic backscatter information. In addition, all spatial filtering operati ons required in the pixel relocation process take the sonar geometry i nto account. Examples of the process are provided by data collected in the Northeastern Pacific over Fieberling Guyot with the SeaMARC II ba thymetric sidescan sonar system and the Sea Beam multibeam echo-sounde r. The nearly complete (90%) Sea Beam bathymetry coverage of the Guyot serves as a reference to quantify the distortions found in the backsc atter images and to evaluate the accuracy of the corrections performed with SeaMARC II bathymetry. As a byproduct, the processed SeaMARC II bathymetry and the Sea Beam bathymetry adapted to the SeaMARC II sonar geometry exhibit a 35m mean-square difference over the entire area su rveyed.