PROCESSING OF SHUTTLE LASER ALTIMETER RANGE AND RETURN PULSE DATA IN SUPPORT OF SLA-02

The second flight of the Shuttle Laser Altimeter (SLA) flew on board the space Shuttle Discovery, during August 1997 during the STS-85 Mission. The nearly 3 million laser shots transmitted during the course of the 11 day SLA-02 mission yielded approximately 590,000 geolocated returns from land and more than 1,500,000 from ocean surfaces. These data were analyzed to produce a data set that provides laser altimetry elevations of high vertical accuracy that can be used for scientific purposes. Processing of the data included the geolocation of surface returns, involving precision TDRSS-tracking based Shuttle orbit determination and pointing bias calibration, ellipsoid to geoid reference frame transformations, conversion of engineering parameters to physical units, application of scaling factors to obtain a consistent measure of the backscatter energy, and classification of the returns based on comparisons with reference elevation data (TerrainBase Digital Elevation Model (DEM) and mean sea level). Additionally, the digitized laser returns were analyzed and modeled using constrained non-linear least-squares optimization techniques. The elevation data were compared to both high-resolution DEMs and a reference ocean surface to assess data accuracy. Ancillary data, such as NDVI (Normalized Digital Vegetation Index) and Land Cover classification data, were also included in the distributed data set. Key aspects of the data analysis are discussed. Further documentation concerning SLA-02 data processing procedures, problems evidenced in the data, and its distribution format is provided in the SLA-02 site (http://denali.gsfc.nasa.gov:8001/).