Corrections for Tidal Residuals Due to Insufficient Representation Using a Single Station in Shallow Water Multibeam Bathymetric Data

Tidal correction is important for shallow water multibeam sonar to ensure vertical accuracy to International Hydrographic Organization Order 1 standards. The number and distribution of tidal control stations have important influences on tidal zoning and reduction. In many cases, tidal residuals will be unavoidable because of tidal representative errors, particularly when using a single tidal station. Tidal residuals cause depth discrepancies in overlapping areas between the two neighboring swaths. They are different from other vertical error sources. For a multibeam survey project, the distance between the tidal control station on the shore and the survey site or the area surveyed in a single day is relatively short. Therefore, the tidal characteristics between them are usually equal. The tidal curve at each bathymetric point in the small area can be recovered by the observed tide at a single station nearby and synchronous multibeam bathymetric data. After other errors have been considered and corrected, the tidal parameters—that is, the time difference of tide, the ratio of tidal ranges, and the direction of tidal wave propagation—can be estimated with the depth discrepancies and the tidal data from a single station using the least squares method. Then, the tidal residuals can be calculated based on the estimated tidal parameters. The quality of final bathymetry can be improved by the corrections as verified by a field test.