Abstract
Shallowwater depth plays an important role in marine development, navigation safety, and environmental protection. It is an efficient and economical way to obtain water depth by remote sensing technology. At present, most empirical models based on multispectral image usually obtain water depth by the relationship between the sea surface reflectance (SSR) (a single pixel) and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> water depth, it is a one-to-one correspondence between the reflectance and depth. However, seafloor substrate and inherent optical properties (IOP) will also have contribution to the SSR. In this article, we propose an adjacent pixels multilayer perceptron model (APMLP) model using adjacent pixels to weaken the influence of seafloor substrate and IOP.Datasets on Oahu Island (Sentinel-2B, LIDAR <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> data) and Saint Thomas Island (Sentinel-2A, LIDAR <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> data) are used to establish and verify the model. The APMLP model are also compared with the multilayer perceptron model (MLP) model, BP neural network model, and Log-ratio model. The overall root-mean-square error (RMSE) of APMLP model on Oahu Island is 0.72 m, which is much better than the other three models (MLP 1.07 m, BP 1.05 m, Log-ratio 1.52 m). Similar results are obtained from the Saint Thomas Island dataset, RMSE of APMLP model is 1.56 m, better than the other three (MLP 1.91 m, BP 1.89 m, Log-ratio 2.39 m). The study confirms that considering adjacent pixels in an artificial neural network model can effectively improve the performance of water depth retrieval.
Highlights
Shallow water depth is important marine hydrological information that plays a guiding role in chart drawing, coastal engineering, marine resource development and management
Most of these methods use the visible bands (420nm-780nm) for water depth inversion. These methods can be roughly divided into two categories: physical models based on hyperspectral remote sensing images (HSIs) and empirical models based on multispectral remote sensing images (MSIs) [14]
Where Rw is sea surface reflectance (SSR); R∞ is the surface reflectance of the optically deep water; Ad is bottom albedo, which is affected by seafloor substrate; 2k is the effective two-ways attenuation coefficient, which is affected by inherent optical properties (IOP), and H is the depth of water
Summary
Shallow water depth is important marine hydrological information that plays a guiding role in chart drawing, coastal engineering, marine resource development and management. Traditional bathymetric surveys are based on field surveys, mainly using ship-borne sonar or airborne lidar [1]. These survey methods have the advantage of high measurement accuracy, but will consume considerable manpower and material resources and may be affected by sea conditions [2]-[4]. Many water depth inversion methods based on RSI have been proposed [8]-[13]. Most of these methods use the visible bands (420nm-780nm) for water depth inversion. These methods can be roughly divided into two categories: physical models based on hyperspectral remote sensing images (HSIs) and empirical models based on multispectral remote sensing images (MSIs) [14]
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