HR: 08:15h
AN: C21B-02    [Abstracts]
TI: Laser Pointing Determination for ICESat Altimetry
AU: Schutz, B E
EM: schutz@csr.utexas.edu
AF: Center for Space Research, University of Texas at Austin, Austin, TX 78746 United States
AU: * Webb, C
EM: webb@csr.utexas.edu
AF: Center for Space Research, University of Texas at Austin, Austin, TX 78746 United States
AU: Bae, S
EM: bae@csr.utexas.edu
AF: Center for Space Research, University of Texas at Austin, Austin, TX 78746 United States
AU: Urban, T
EM: urban@csr.utexas.edu
AF: Center for Space Research, University of Texas at Austin, Austin, TX 78746 United States
AB: Since its launch aboard the Ice, Cloud, and land Elevation Satellite (ICESat) in January 2003, the Geoscience Laser Altimeter System (GLAS) has produced high-quality elevation profiles for the Greenland and Antarctic ice sheets, as well as for other land and ocean surfaces, during five operational periods. The computation of individual elevations begins with a scalar range, inferred from the time required for a single pulse to travel from a reference point in the GLAS instrument to the surface, and back. This value is then combined with the laser-pointing direction, determined from ground-based processing of data collected by the uniquely designed, on-board Stellar Reference System (SRS). The resulting range vector, together with the geocentric position vector of the GLAS reference point, defines the position and the elevation of the laser spot on the surface. Consequently, while the accuracy of a GLAS-derived elevation depends on the knowledge of the instrument position, as with radar altimeters, it also depends directly on the knowledge of the laser-pointing direction. The position of the GLAS reference point is obtained through ground-based precision orbit determination (POD), using the navigation data collected by the on-board BlackJack GPS receiver. Current assessment of these results suggests that the critical radial component has an accuracy of 2-3 cm, well within the 5-cm requirement. Faced with a number of challenges in the SRS after launch, significant effort has been expended to calibrate the laser-pointing determination. Through a series of refinements in the precision attitude determination (PAD), the resulting pointing solutions have steadily improved the accuracy of the computed elevations, as determined through a variety of calibration/validation techniques. This presentation will highlight the improvements observed for elevation data obtained during the first two operations periods, February-March and September-November 2003.
DE: 1894 Instruments and techniques
DE: 1294 Instruments and techniques
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting