On-Site Calibration-Based Estimation Method of Forward Seabed Elevation Using Forward Scan Sonar

This paper addresses a novel calibration-based estimation method to measure the forward seabed elevation (FSE) where an area illuminated by forward scan sonar (FSS) for unmanned underwater vehicles (UUVs). The conventional method measures the FSE using one or two down-facing single-beam sonars; this method can, however, cause errors. In order to accurately measure the FSE, a sensor capable of measuring the 2D space of the seabed is needed, such as FSS. The method proposed in this work consists in estimating the FSE, by analyzing the acoustic beam distribution characteristics of FSS. A novel FSS beam distribution model is proposed, which simplifies beam distribution characteristics. Then, on-site calibration is conducted to estimate the parameters of this model. Based on the estimated model, templates can he generated and compared with FSS data acquired at the experiment in order to estimate geometrical information at the FSE. The FSE of the best matched template is the estimated FSE of the FSS data acquired in the experiment. In order to verify the performance of the proposed method, experiments using an UUV were carried out in an indoor water tank. We also verified that the proposed method performed well even when there were objects on the seabed.