A Crossover Evaluation and Calibration Method for Geolocation Error of Spaceborne Photon-Counting Laser Altimeter

The Ice, Cloud and Land Elevation Satellite (ICESat-2) offers an unprecedented high density of laser data on the Earth’s surface. Evaluation and calibration of geolocation errors are important for the scientific application of laser data. In this study, a crossover method is proposed to evaluate and calibrate errors. This method mainly relies on small-scale reference data and consistency conditions at the trajectory crossovers. By matching the profile measurements of the ascending and descending altimeter tracks to find the location where the crossover discrepancy is minimized, the geolocation errors of the wide-area laser data are estimated. Three years of ICESat-2 measurements over the Ridgecrest (CA19) in the southern United States and McMurdo Dry Valleys (MDV) in eastern Antarctica were used to test the performance of the method. It was shown that the method can be used to estimate the geolocation error of the ICESat-2 laser data, which ranged from 4.65 to 5.62 m for both sites. After calibration, the mean absolute error of the crossover discrepancies was reduced by approximately 50%. In addition, with the reference digital elevation model (DEM) as the true value, the elevation accuracy (RMSE) of the laser data at the CA19 site improved from 0.38 m before calibration to 0.34 m after calibration, and the improvement at the MDV site was even more significant, about 0.22 m. In conclusion, the proposed method is effective and feasible and can improve the consistency of long-period laser data quality in large areas.