The Effect of Terrestrial Surface Slope and Roughness on Laser Footprint Geolocation Error for Spaceborne Laser Altimeter

The quality of spaceborne laser altimeter observation mainly depends on the geolocation accuracy of laser footprint. To thoroughly analyze the footprint geolocation errors, mathematical models of Root-Mean-Square Error (RMSE) of laser footprint geolocation are established based on footprint geolocation procedure and principle of error propagation. Taking Geoscience Laser Altimeter System (GLAS) as an example, the influences of surface slope and roughness on the RMSE of laser footprint geolocation (LFG) are simulated. The simulation results for nine representative terrains indicate that the horizontal errors are constant of 5.86 meters that mainly caused by instrument mounting errors, laser pointing errors, and platform attitude errors; while the vertical error increases from 0.07 m to 2.49 m, which is primarily contributed by the laser pointing error. To validate the proposed mathematical model, 20 reference LFG differences are computed by the differences of original geolocation of GLAS and refined footprint geolocation based on a waveform matching method with coincident airborne Light Detection and Ranging (lidar) data. The validated results prove that the RMSE models of laser footprint geolocation are applicable in evaluating performance and sensor error allocations of spaceborne laser altimeter.