Abstract
To obtain the high-resolution seabed topography and overcome the limitations of existing topography reconstruction methods in requiring external bathymetric data and ignoring the effects of sediment variations and Side-Scan Sonar (SSS) image quality, this study proposes a method of reconstructing seabed topography from SSS images with a self-constraint condition. A reconstruction model is deduced by Lambert’s law and the seabed scattering model. A bottom tracking method is put forward to get the along-track SSS towfish heights and the initial seabed topography in the SSS measuring area is established by combining the along-track towfish heights, towfish depths and tidal levels obtained from Global Navigation Satellite System (GNSS). The complete process of reconstructing seabed topography is given by taking the initial topography as self-constraint and the high-resolution seabed topography is finally obtained. Experiments verified the proposed method by the data measured in Zhujiang River, China. The standard deviation of less than 15 cm is achieved and the resolution of the reconstructed topography is about 60 times higher than that of the Digital Elevation Model (DEM) established by bathymetric data. The effects of noise, suspended bodies, refraction of wave in water column, sediment variation, the determination of iteration termination condition as well as the performance of the proposed method under these effects are discussed. Finally, the conclusions are drawn out according to the experiments and discussions. The proposed method provides a simple and efficient way to obtain high-resolution seabed topography from SSS images and is a supplement but not substitution for the existing bathymetric methods.
Highlights
High-resolution seabed topography has important applications in offshore oil exploration [1], underwater target detection [2], marine eco-environmental protection [3,4], underwater navigation and localization [5] and many other fields
To simplify the reconstruction and get accurate seabed topography without the constraint of external bathymetric data, this paper proposes a novel method to reconstruct seabed topography from Side-scan sonar (SSS) images with the SSS self-constraint which can be obtained by combining the SSS towfish height from the SSS waterfall image, the SSS towfish depth provided by a built-in pressure sensor and Global Navigation Satellite System (GNSS)
Equation (13) shows that the seabed topography can be reconstructed from SSS images if the initial topography z0 is given. z0 is often provided by external bathymetric data, which means an extra measurement must be done
Summary
High-resolution seabed topography has important applications in offshore oil exploration [1], underwater target detection [2], marine eco-environmental protection [3,4], underwater navigation and localization [5] and many other fields. To get absolute seabed topography from the SSS image, many scholars developed different seabed reconstruction methods [17,18,19,20,21,22] These studies can be classified into two categories according to whether the reconstruction needs the external bathymetric data. The method obtained the position and seabed height of the first echo of each ping using the external bathymetric data firstly, and built seabed elevation maps from SSS waterfall images according to the propagation principle of acoustic wave in water. Without the external bathymetric data, Dura et al analyzed the propagation method and pointed out that the method simplifies the reconstruction of seabed topography, but it is more sensitive to noise and abnormal ping measurement, and they proposed a linear method to reconstruct the textured seabed from synthetic SSS images [21]. Combining Equations (3)–(7) to compute z, the reconstructed topography can be obtained
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