Pre-processing algorithm and P-SAS processing applied to underwater acoustic data of a 2D scanning on a dump site in the sea

In underwater imaging, Planar Synthetic Aperture Sonar (P-SAS) technique has been validated on both simulated and tank data. It showed a significant improvement of 3D representation of bottom and sub-bottom. In this paper we present its application to real data acquired during sea experiments on a dump site in the Baltic sea. Data were acquired during a European project “SITAR” (Seafloor Imaging and Toxicity: Assessment of Risks caused by buried waste). The transmitter was a Topographic Parametric Sonar (TOPAS) fixed on a ROV which position was monitored. Two central frequencies were explored, 10 kHz and 20 kHz. As P-SAS algorithm was designed for data obtained on a regular planar grid important modification were required to handle real sea data and “realistic” navigation conditions (irregular grid): a “rearrangement” algorithm was designed for preprocessing actual data and correct trajectory disturbances (in 2D). This algorithm is the re-projection of data positions to a new (virtual) regularly grid. The algorithm was validated on tank experimental data prior to application to sea data. P-SAS processed data will be presented. A strata representation technique was used for analyzing the seafloor and the sub-bottom and for locating buried objects on the scanned dump site.