An On-Orbit Calibration Model for Full-Waveform Laser Altimeters by Matching Single-Modal and Multimodal Waveforms

Accurate pointing and ranging calibration are essential for laser altimeters to obtain the geolocation accuracy required for further scientific application. Waveform matching is an economical and effective on-orbit calibration technique that involves simulating waveforms based on the vertical structure within potential correct footprints acquired from high-resolution digital surface/elevation model and comparing them with the recorded waveforms to correct the footprint geolocation. We propose an on-orbit calibration model using waveform matching by integrating multimodal waveforms and single-modal waveforms. The model fully leverages the characteristics of multimodal waveforms that can be accurately located through waveform matching, and the single-modal waveforms that can precisely measure elevation, achieving an enhancement in performance over the classical model. To validate the effectiveness of the improved calibration model, we conducted experiments using global ecosystem dynamics investigation (GEDI R02) to correct the potential positioning bias in GEDI measurements. The eight beams were adjusted between -2 and 8 m in the north and east directions, with corresponding adjustments in laser pointing from 2.5 to 4 arcsec in both roll and pitch. Range corrections varied from -2 to -15 cm. The results demonstrate that the geolocation accuracy is markedly improved for all eight beams, with the elevation bias reduced by approximately 10 cm and the planar bias restricted to within 3 m (coverage beams) and 1 m (full-power beams). The model can be used to effectively calibrate full-waveform laser altimeters and also provides new insights into the verification of the system's accuracy.