A Novel Ray Tracing Approach for Bathymetry Using UAV-Based Dual-Polarization Photon-Counting LiDAR

Unmanned aerial vehicle-based photon-counting ocean bathymetric light detection and ranging (LiDAR) systems rapidly acquire topographic data from islands, reefs, and shallow waters. However, the bathymetric ability of seabed topography is affected by high backscattering from the sea surface owing to its proximity, and no suitable imaging models are available. Herein, we designed a novel ray approach for bathymetry based on a dual-polarization photon-counting LiDAR. Based on the transmission characteristics of light, a dual-polarization channel strategy was proposed, and the data from two channels in vegetation, sand, and shallow and medium-depth waters were compared. Based on the ray tracing method, imaging models of the water surface and depth for light and small photon-counting LiDAR were established. Shallow-water experiments were conducted near Jiajing Island, Hainan, China, to verify the accuracy of the LiDAR bathymetry data by shipborne single-beam sounding data. The results indicate that the vertical polarization channel data had a high signal-to-noise ratio in the terrestrial part, while the horizontal polarization channel had a better water surface backscatter suppression effect and strong bathymetry ability in the water part. The detectable depth was approximately 8 m in the experimental area. The MAEs of the depth values of the LiDAR point cloud before and after refraction correction relative to the single beam depth measurement values were 1.08 and 0.09 m, respectively. And the RMSEs before and after correction were 1.12 and 0.11 m, respectively.