Passive Ground-Based Optical Techniques for Monitoring the On-Orbit ICESat-2 Altimeter Geolocation and Footprint Diameter

Corner cube retro-reflectors (CCRs), passive optical components, are used to independently evaluate the geolocation accuracy and effective laser footprint diameter of NASA's laser altimetry mission, ICESat-2, at two specific study sites: White Sands Missile Range in New Mexico and along a segment of the 88 degrees S line of latitude in Antarctica. The CCR methodology provides ICESat-2 the ability to monitor these altimeter performance metrics throughout the mission lifetime as an indicator of the health of the instrument and the quality of the observations for science applications. The results using this technique reveal a mean geolocation accuracy of the ICESat-2 measurements of 3.5 m +/- 2.1 m, meeting the mission requirement of 6.5 m. For those instances where multiple CCRs are illuminated, the mean effective laser footprint diameter is 10.9 m +/- 1.2 m, with the variability assumed to be due to the influence of atmospheric conditions, but warrants further investigation.