PWD: polarization-based waveform decomposition method for airborne lidar bathymetry in very shallow waters

Airborne lidar provides high-accuracy, efficient, and continuous mapping of land and seafloor topography in nearshore and island regions. However, accurate retrieval of very shallow water depths is hindered by the mixing of lidar signals from the surface and bottom. Here, we propose a polarization-based waveform decomposition method (PWD) to achieve land-sea topographic detection. By exploiting the polarization differences between the water surface and bottom, this method jointly uses the co-polarized and cross-polarized channels to estimate the initial positions. Subsequently, a waveform decomposition method is employed to separate the water surface and bottom signals from mixed waveforms, enabling accurate water depth retrieval. The accuracy and robustness of this method were validated through field experimental data obtained by airborne lidar. The results demonstrate that the water depth retrieved by the PWD method shows strong consistency with the results from the benchmark green/NIR method, with a root mean square relative deviation (RMSRD) of 13.67% and a coefficient of determination (R^2) of 0.9190. This method provides a new pathway, to our knowledge, for efficient integrated land-sea surveying, supplying reliable data for terrain detection and environmental monitoring.