Examining the Derived Sea Wave Heights From ICESat-2 Weak Beams: A Case Study in Marginal Seas

The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) carries the new generation spaceborne photon-counting lidar, Advanced Topographic Laser Altimeter System (ATLAS). ICESat-2/ATLAS has an excellent performance for obtaining precise geometric surface profiles of land and oceans, by which the surface parameters such as the significant wave height (SWH) over oceans can be further obtained. As the strong beams have better data quality, they are currently used to obtain the sea surface parameters. The weak beams could double the spatial coverage area if they can also be successfully used. However, this potential is constrained by the lower signal-to-noise ratio (SNR) of weak beams. To exploit the performance of weak beams, this study proposes a method to extract sea surface signal photons, which are further accumulated to calculate the SWHs. This study explores the effect of the data processing window length on the result of the denoising algorithm and how many sea surface signal photons should be accumulated to estimate the reliable SWHs with ICESat-2 weak beams. The calculated SWH shows good agreement with ECMWF reanalysis 5 (ERA5) data, with the root mean square error (RMSE) under 0.3 m. The method proposed in this study enables the acquisition of SWH values in certain regions where no ATL12 official data are available.