HR: 1330h
AN: C32A-0439    [PDF]
TI: Calibration and Validation Tools for the ICESat Mission: Waveform Matching.
AU: * Carabajal, C C
EM: claudia@stokes.gsfc.nasa.gov
AF: NVI, Inc.@NASA/Goddard Space Flight Center, Laboratory for Terrestrial Physics - Code 926, Greenbelt, MD 20771 United States
AU: Harding, D J
EM: David.J.Harding@nasa.gov
AF: NASA/Goddard Space Flight Center, Laboratory for Terrestrial Physics - Code 921, Greenbelt, MD 20771 United States
AB: The ICESat laser altimeter mission provides measurements of elevation data around the globe, cloud and aerosol heights, as well as land topography and vegetation characteristics. For the calibration and validation phase of the mission, we have developed a waveform-matching tool with the purpose of discriminating between geolocation solutions, assessing spacecraft pointing to off-nadir targets, validating laser altimeter beam quality parameters such as pulse width, footprint diameter and circularity, and validating footprint derived parameters including mean elevation, slope, roughness and vegetation height. The Geoscience Laser Altimeter System (GLAS) aboard ICESat digitizes the backscattered laser energy (i.e., waveform). Observed GLAS waveforms are compared to synthetic waveforms produced from high resolution Digital Elevation Models (1-5 m grid spacing) using a simplified, noise free, model of the intrument's characteristics, including pulse width and far-field energy pattern, and receiver FOV transmission and impulse response. The grid-based waveform simulations are used to reproduce the instrument's interaction with the topographic surface at the footprint location. Optimal matches are determined by minimizing the observed-to-simulated waveform residuals using an iterative spatial search. Correlation between within footprint surface height distribution as recorded in the observed and simulated waveforms is computed while shifting the location of the footprint within the DEM until the optimal location is determined. For the simulation we utilize high-resolution, airborne laser altimeter data from which 1.8 m bare-earth and canopy-top grids are derived for the Puget Lowland area in Washington State. Complex waveforms created by vegetation cover and building edges enhance precision in the validation of geolocation solutions, spacecraft pointing, and waveform-derived parameters for highest, centroid and lowest within-footprint elevations.
DE: 1294 Instruments and techniques
DE: 1640 Remote sensing
DE: 1645 Solid Earth
DE: 1694 Instruments and techniques
SC: Cryosphere [C]
MN: 2003 Fall Meeting