HR: 08:30h
AN: C31A-03 INVITED     [PDF]
TI: ICESat Laser Altimetry: Calibration/Validation
AU: * Schutz, B E
EM: schutz@csr.utexas.edu
AF: Center for Space Research, University of Texas at Austin/R1000, Austin, TX 78712-1085 United States
AB: The Geoscience Laser Altimeter System (GLAS) was launched on ICESat in January 2003 into a 600 km altitude, near polar orbit from Vandenberg, California. The GLAS instrument has been developed by NASA Goddard and it was mated to the spacecraft bus, built by Ball Aerospace, in June 2003. GLAS laser-1 was activated in orbit on February 20, 2003 and elevation profiles of the Greenland and Antarctic ice sheets, as well as land and ocean profiles, have been produced using the 1064 nm wavelength. The laser pulse has a divergence of about 0.11 mrad, which illuminates a spot on the surface with a 66 m diameter. The 170 m spot separation on the surface is determined by the ICESat orbital motion and the 40 Hz laser pulse repetition rate. Unlike wide pulse radar altimeters, accurate knowledge of the laser beam direction is required for the laser altimeter to produce accurate surface profiles. The laser pointing direction is determined with the assistance of an innovative system of CCD cameras plus calibration/validation methodologies. The combination of the laser pulse round trip time of flight and the pointing determination system provides an altitude vector. Determination of the direction of the altitude vector has an accuracy requirement of about 1.5 arcsec (or about 4.5 m on surface). In addition to the instrumentation required to produce the altitude vector, the position of a GLAS reference point with respect to the center of mass of the Earth is required. The ICESat BlackJack GPS receiver from NASA JPL has enabled determination of the radial component of the orbit to a few centimeter accuracy level. Laser-1 operated in orbit with a ground track that was controlled to within 800 m of an 8-day repeat reference track. During laser-1 operation and after the laser ceased firing on March 29, experiments were conducted to assess and improve the accuracy of off-nadir pointing, a unique capability to enhance the science return. This paper will provide an assessment of the accuracies achieved by laser-1 and during laser operations with the additional GLAS lasers. On-orbit factors, such as thermal and jitter effects, that may limit the achieved accuracy will be discussed. These assessments will draw on calibration/validation experiments that have been conducted as well as the analysis of the on-board instrumentation.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 1824 Geomorphology (1625)
DE: 1827 Glaciology (1863)
DE: 4556 Sea level variations
DE: 9805 Instruments useful in three or more fields
SC: Cryosphere [C]
MN: 2003 Fall Meeting