Large vs. small scale multibeam mapping in deep areas

Multibeam systems are powerful tools for a variety of studies, from bathymetry to morphostructural analysis, from cable route reconnaissance to site surveying. These systems can provide complete coverage of the seafloor areas surveyed, thus releasing large volumes of data. Using multibeam systems for large scale bathymetric mapping in deep waters (e.g. 1:250000, with 25-50 m contours, at several thousand meters depth) often requires no more than 50% of the total amount of data acquired. This is because the high concentration of data in the smallest spatial cell which can be defined at these scales allows the drafting of publishable maps without significant loss of topographic resolution. The situation changes drastically when these great amounts of data are used to draw more detailed maps (e.g. 1:25000, with 5-10 m contours) at the same depths. Unexpected patterns could appear in the drawing of the isolines. Short wavelength regular patterns with a constant orientation could be due to minor failures in the acquisition system (e.g. small errors in roll, heave and pitch calibrations). They can be due also to the inherent maximum resolution of these kind of systems working at several thousand meters depth. Filtering of these patterns is not easy because they have the same spatial resolution as the actual morphology to be solved. The volume of data provided by multibeam systems working in deep waters is often more than enough to produce standard large scale bathymetric maps, but provide sufficient resolution when detailed scales are applied