Coastal bathymetry mapping
There is lack detailed bathymetry data in many parts of the world. Sonar-based hydrographic mapping is time consuming and expensive, and hydrographic survey ships cannot access some of the most shallow coastal areas.
Bathymetric estimates derived from satellite data can achieve good accuracies in such areas, especially if supported by some in situ depth measurements. If so, bathymetric retrieval is relatively fast, and can be quite accurate. Where no in situ data are available, analytical model inversion can retrieve water depth and bottom type simultaneously, but the method is time consuming. The retrieval requres water quality information. If this is not available from independent measurements it must be retrieved from the satellite data. In this case the, accuracy of the bathymetric maps may be reduced, particularly in areas where water quality is spatially variable.
Bathymetric accuracy and vertical resolution depend on water quality and water depth. In clear oceanic waters results are reliable down to 15-20m. For very shallow water accuracies may be a high as 10cm, but reach 1-2m in depth over 6 m. In turbid coastal waters maximum depths and accuracies drop significantly.
In regions with persistent cloud cover for much of the year it may be difficult to find suitable satellite data. However, bathymetric mapping is typically a one-off activity and thus not time-critical. The exception is areas where the bathymetry can change rapidly over relatively short time scales, such as river estuaries, sand dunes and deltas.