Arcsecond-level pointing calibration for ICESat laser altimetry of ice sheets

Abstract.

 Arcsecond-level accuracy of NASA's ICESat (Ice, Cloud, and land Elevation Satellite) satellite laser altimeter beam pointing angle is required to satisfy the scientific goal of detecting centimeter-level elevation changes, over time, in the Greenland and Antarctic ice sheets. Two different approaches, termed “topographic inferred” and “direct detection”, were examined for calibrating the laser pointing angle (that is, detecting and removing pointing determination bias) at the 1.5-arcsec level, using information independent of the onboard pointing instrumentation. Both approaches entail estimating the beam pointing by differencing the three-dimensional position of the altimeter instrument and the laser-beam spot (or “footprint”) location on the ground. Analytical assessments of the two approaches are discussed, along with recommendations for the ICESat pointing determination calibration strategy.