Surveys by Multibeam Echosounders 1. More slanted beams sometimes returns irregular soundings, since they are more refracted by sound velocity distribution, and their footprints become larger. In order to distinguish peaks from noises and to ensonify shaded zones behind shallows, swathes from adjacent survey lines should be enough overlapped. In case we miss foreign bodies, adjacent swathes should be enough overlapped. Since dredged face sometimes can shades dredged bottom, we should plan such survey lines that can ensonify the face and inside dredged area.
Same way is applicable at wharf frontage.
In order to obtain accurate soundings, it is required to compensate biases of motion sensor and time latencies. When sonar head is permanently installed on the under-hull, changes of these biases are not expected to be large. It is recommended to set a fixed test area around a specific topographic feature and to perform patch test in the same area every time. Here we figure out the points to survey efficiently and to obtain valid soundings for nautical chart. Checking irregular values of motion sensor It is sometimes reported that motion sensors output irregular values in some condition.