Multibeam data cleaning for hydrography using geostatistics

The French Naval Oceanographic and Hydrographic Service (SHOM) operates two multibeam echo sounders for hydrographic surveys. These systems provide a full coverage of the sea bed with a fine resolution. The data sets contain sparse erroneous soundings which must be detected and removed. Cleaning methods in use are mainly manual. They ensure high quality data sets but they represent a considerable human workload. To reduce the cost of the data cleaning, SHOM is studying automatic algorithms to detect dubious soundings. This article presents three algorithms developed by the “Centre de Geostatistique-Ecole des Mines de Paris” and based on geostatistical techniques. The first algorithm tests the median of the depth increments between the selected sounding and its neighbours; the second algorithm defines an acceptance interval from the quantities of the local distribution of the depth; the third one is a cross validation in which the kriging error is compared with the kriging standard deviation. These algorithms have been integrated in the data cleaning system developed at SHOM. The raw data set is first processed by the detection algorithms then the operator controls the detected data. The first tests on board show a dramatic reduction in the processing time with an increase in quality