Abstract
Shallow water bathymetry is critical in understanding and managing marine ecosystems. Bathymetric inversion models using airborne/satellite multispectral data are an efficient way to retrieve shallow bathymetry due to the affordable cost of airborne/satellite images and less field work required. With the increasing availability and popularity of unmanned aerial vehicle (UAV) imagery, this paper explores a new approach to obtain bathymetry using UAV visual-band (RGB) images. A combined approach is therefore proposed for retrieving bathymetry from aerial stereo RGB imagery, which is the combination of a new stereo triangulation method (an improved projection image based two-medium stereo triangulation method) and spectral inversion models. In general, the inversion models require some bathymetry reference points, which are not always feasible in many scenarios, and the proposed approach employs a new stereo triangulation method to obtain reliable bathymetric points, which act as the reference points of the inversion models. Using various numbers of triangulation points as the reference points together with a Geographical Weighted Regression (GWR) model, a series of experiments were conducted using UAV RGB images of a small island, and the results were validated against LiDAR points. The promising results indicate that the proposed approach is an efficient technique for shallow water bathymetry retrieval, and together with UAV platforms, it could be deployed easily to conduct a broad range of applications within marine environments.
Highlights
Shallow water regions’ bathymetry is important in various managements and modelling, such as navigation and transportation [1], modelling of sediment deformation [2], coastal line or water bank erosion [3,4], and the needs of sand mining and beach nourishment [5].Bathymetry retrieval techniques can be sorted into two broad categories according to the principals that are used: geometric measurements and radiometric measurements
With the rapid development of unmanned aerial vehicle (UAV) technology, bathymetry acquisition directly based on UAV RGB images is efficient and low-cost when compared to sound-based methods or LiDAR
We used the projection image based two-medium stereo triangulation method to obtain water depths; the obtained depths were used as the water depth references for the Geographical Weighted Regression (GWR) model
Summary
Shallow water regions’ bathymetry is important in various managements and modelling, such as navigation and transportation [1], modelling of sediment deformation [2], coastal line or water bank erosion [3,4], and the needs of sand mining and beach nourishment [5]. Bathymetry retrieval techniques can be sorted into two broad categories according to the principals that are used: geometric measurements and radiometric measurements. Geometric methods are based on the signal/ray travel return time to calculate the distance or using two or multiple optical rays to triangulate the depths; these methods include traditional echo sounding [6], two-medium photogrammetric triangulation [7,8], LiDAR [9], and so on. Radiometric methods (refer as satellite-derived bathymetry (SDB) methods) [10,11,12,13] are based on radiative transfer, where atmosphere composition and water column, as well as seabed type and composition, will affect the spectral information acquired using multispectral/hyperspectral imaging sensors. SDB methods usually use inversion models to infer the depth information.
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