HR: 17:30h
AN: C34A-07    [Abstracts]
TI: ICESat Receiver Signal Dynamic Range Assessment and Correction of Range Bias due to Saturation
AU: * Sun, X
EM: Xiaoli.Sun-1@nasa.gov
AF: NASA Goddard Space Flight Center, Code 694 B33, Room D424, Greenbelt, MD 20771 United States
AU: Abshire, J B
EM: James.B.Abshire@nasa.gov
AF: NASA Goddard Space Flight Center, Code 694 B33, Room D424, Greenbelt, MD 20771 United States
AU: Yi, D
EM: Xiaoli.Sun-1@nasa.gov
AF: SGT, Inc.,/NASA Goddard Space Flight Center, Code 614.1, Greenbelt, MD 20771 United States
AU: Fricker, H A
EM: hafricker@ucsd.edu
AF: Institude of Geophysics and Planetary Physis/Scripps Institude of Oceanography, University of California, San Diego 9500 Gilman Dr, La Jolla, CA 92093-0225 United States
AB: The laser echo pulse signals for Earth orbiting laser altimeters have a large dynamic range due to the variabilities in the Earth's surface reflectivity, scattering angles, and atmosphere conditions. The echo pulse energies received by the Geoscience Laser Altimeter System (GLAS) on the ICESat mission vary over 4 orders of magnitude. Echo pulse energies measured over ice and snow surfaces are 2 to 3 times stronger than those expected, which were based on prior passive measurements and by assuming Lambertian scattering surfaces. Echo pulse energies from still water surfaces are several hundred times stronger, due to the narrow solid angle of the specular reflections. Attenuation by clouds and aerosols also cause a large and rapid variation in the received signal. As a result, many of the echo pulses exceed the linear dynamic range of the GLAS altimeter receiver and partially saturate the detector electronics. The recorded pulse waveform is distorted when the receiver is saturated, causing a significant bias in the GLAS range, surface slope, and surface reflectance measurements. We have characterized the properties of the GLAS altimetry detector beyond its linear dynamic range. We did this in the laboratory using a flight spare detector assembly and a calibrated laser diode test source. The results show the highly reproducible effects of detector saturation on the range measurements. A simple algorithm can be used to correct the range bias to within 5 cm for signals from flat ice and snow surfaces. The algorithm was tested using the GLAS measurements over Salar de Uyuni, Bolivia, where the surface elevation of the dry salt-lake had been surveyed with cm-level resolution with GPS receivers. The results show that the GLAS range measurements with the range bias correction agree with surface elevations to within 2 cm in absolute range and 3 cm in standard deviation. The algorithm is being incorporated into the GLAS data products. We are currently extending the approach and algorithm to correct for echo pulse width and energy measurements over a larger signal dynamic range. It appears that range bias for GLAS measurements over still water surface can be corrected to within 10 cm.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 1640 Remote sensing (1855)
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
SC: Cryosphere [C]
MN: Fall Meeting 2005