Abstract
Side-scan sonar (SSS) is used for obtaining high-resolution seabed images, but with low position accuracy without using the Ultra Short Base Line (USBL) or Short Base Line (SBL). Multibeam echo sounder (MBES), which can simultaneously obtain high-accuracy seabed topography as well as seabed images with low resolution in deep water. Based on the complementarity of SSS and MBES data, this paper proposes a new method for acquiring high-resolution seabed topography and surface details that are difficult to obtain using MBES or SSS alone. Firstly, according to the common seabed features presented in both images, the Speeded-Up Robust Features (SURF) algorithm, with the constraint of image geographic coordinates, is adopted for initial image matching. Secondly, to further improve the matching performance, a template matching strategy using the dense local self-similarity (DLSS) descriptor is adopted according to the self-similarities within these two images. Next, the random sample consensus (RANSAC) algorithm is used for removing the mismatches and the SSS backscatter image geographic coordinates are rectified by the transformation model established based on the correct matched points. Finally, the superimposition of this rectified SSS backscatter image on MBES seabed topography is performed and the high-resolution and high-accuracy seabed topography and surface details can be obtained.
Highlights
Seabed topography and morphology provide fundamental information for marine scientific research and ocean engineering [1,2,3,4]
The features existed on the seabed are relatively simple and the detected edge and point features can be represented by similar Speeded-Up Robust Features (SURF) descriptors, which may decrease the distinctiveness of SURF descriptors
Because of the two factors, even when two feature points in the side-scan sonar (SSS) and multibeam echo sounder (MBES) images are distant, they may be regarded as matches when they are represented by similar SURF descriptors
Summary
Seabed topography and morphology provide fundamental information for marine scientific research and ocean engineering [1,2,3,4]. The SSS is usually installed in a towfish and towed by a cable behind a surveying vessel (Figure 1a) It emits a wide-angle beam and receives thousands of seabed echoes at fixed time intervals to form a high-resolution seabed image [5,8]. The output from 3DSS is in the form of an intensity point cloud, which can be post-processed either as bathymetry, backscatter seabed image or a combination of both. This kind of data has been found less capable in the detection of seabed targets [16]. These new sonar systems have restrictions and their performances in the field of bathymetry measurement are usually inferior to those obtained by MBES [6]
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