Underwater Slope Measurement Using a Tilted Multibeam Sonar Head

In bathymetric sounding surveys, the most common way of approaching water/shore boundaries is to rotate the sonar head to some angle such that the outer sound beam is parallel to the water surface. If the setup of a sonar head and the position of peripheral devices have a fixed angle of deviation during multibeam sounding, the deviations of roll angle, pitch angle, and yaw angle will result in measurement errors. To allow users to accurately identify the topographic slope, in such an environment, the deviation of different setup angles reflected by the survey results is determined. An experiment using a Seabat 9001s sounder is performed inside the Wushe Reservoir, Taiwan. Results prove the error response proposed by the study and the method of calibrating various deviation angles based on the measurement. Sound waves can also produce “multipath” errors which seriously affect the measurement at steep dam bottoms. Strategies that may be adopted include shortening the distance between the sonar head and the target, keeping the survey line as close to the coastline as possible and, also, keeping it a certain distance from the slope to obtain measurements that are stable at the bottom.