Swath mapping system processing: Bathymetry and cartography

Abstract

During swath mapping cruises various geophysical data were collected. Bathymetry, imagery and other geophysical information require specialised post-processing. Dedicated software enables post-processing and visualisation of each type of data. A graphic interface collects the files and exports them to a CAD system for cleaning and for adding extra information. The huge amount of soundings from multibeam echo sounder systems and the very particular sampling along and across the ship's track demand powerful software such as TRISMUS provides. Major steps in the processing are the merging of raw soundings with navigation corrected if necessary, the cleaning of soundings with a band-pass filter and the gridding of the data to obtain a Digital Terrain Model. Despite care and real time filtering during the acquisition phase, some errors persist and appear as abnormal patterns on contoured maps. It is often difficult to distinguish the origins of the errors and consequently to correct them in a deterministic way. But the analysis and description of typical patterns allows errors to be classified into five groups — sounding, profile, overlap area, surveyed area or gridding artefact — and in some cases to adopt specific processing techniques to reduce or cancel undesirable effects. Merging bathymetric maps and sonar mosaics can be achieved with IMAGEM or with the high level graphic interface MFEDIT. Since dedicated software splits the information up into different layers, the operator can manage the layers according to the information he wants on the final document. Additional information such as seismic reflection data and interpretation, geological logs and legends, can be imported or created as extra layers.