Abstract
Accurate bathymetric maps are essential to understand marine and coastal ecosystems. With the development of satellite and sensor technology, satellite-derived bathymetry (SDB) has been widely used to measure the depth of nearshore waters. Employment of physics-based methods requires a series of optical parameters of the water column and seafloor, which limits the application of these methods to shallow-water bathymetry. Due to convenience, low costs, and high efficiency, empirical methods based on <i>in situ</i> measurements and satellite imagery are increasingly used for nearshore bathymetry. These measurements are required to calibrate empirical models, so that reasonable accuracy can be achieved. The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2), equipped with the advanced topographic laser altimeter system, provides a novel opportunity for nearshore bathymetry. Using the new measurement strategy of photon counting, ICESat-2 can provide accurate bathymetric points from spaceborne observations, which can be used in place of <i>in situ</i> water depth data. In this study, ICESat-2 bathymetric points and multispectral images were used to train four typical models and produce bathymetric maps for Shanhu Island, Ganquan Island, and Lingyang Reef in the Xisha Islands of China. We evaluated the bathymetric results by comparing them with reference depth data from airborne light detection and ranging. All models had a satisfactory accuracy, as well as multimodel and multisource image consistency. With the ICESat-2 bathymetric points, SDB is no longer limited by <i>in situ</i> measurements. Hence, this approach could be extended to a larger scale to obtain nearshore bathymetric maps of coastal areas, surrounding islands, and reefs using free and open-access satellite data.
Highlights
D ETAILED and accurate nearshore bathymetry is critical for a variety of applications, including offshore navigation, ocean research, and marine spatial management [1], [2]
The airborne light detection and ranging (LiDAR) bathymetry (ALB) system with a 532 nm laser beam is widely used in nearshore applications, but it has low efficiency and high costs; further, it is affected by weather and environmental conditions [12]
Satellite-derived bathymetry based on remote sensing images and in-situ measurements is the commonly used method of obtaining bathymetric maps, which can be classified into two categories according to the principle [30]
Summary
D ETAILED and accurate nearshore bathymetry is critical for a variety of applications, including offshore navigation, ocean research, and marine spatial management [1], [2]. The main objective of nearshore bathymetry is to assess shallow water regions around. Two of the most widely used techniques, single or multibeam echo-sounding, and airborne light detection and ranging (LiDAR), have been successfully applied in various coastal and marine regions [7], [8], [9], [10]. Echo-sounding hydrographic survey techniques acquire high-accuracy bathymetric data, which are difficult to collect in areas of shallow water or near reefs, rocks, and similar hazards [11]. The airborne LiDAR bathymetry (ALB) system with a 532 nm laser beam is widely used in nearshore applications, but it has low efficiency and high costs; further, it is affected by weather and environmental conditions [12]. One method of solving these problems uses satellitederived bathymetry (SDB)
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