ICESat Altimetry Data Product Verification at White Sands Space Harbor

Three unique techniques have been developed to validate the Ice, Cloud, and Land Elevation Satellite (ICESat) mission altimetry data product and implemented at White Sands Space Harbor (WSSH) in New Mexico. One specific technique at WSSH utilizes zenith-pointed sensors to detect the laser on the surface and enable geolocation determination of the altimeter footprint that is independent of the data product generation. The system of detectors also registers the laser light time of arrival, which is related to the data product time tag. Several overflights of the WSSH have validated these time tags to less than 3plusmn1 mus. The ground-based detector system also verified the laser illuminated spot geolocation to 10.6 m (3.5 arcsec) plusmn4.5 m on one occasion, which is consistent with the requirement of 3.5 m (1sigma). A third technique using corner cube retroreflector signatures in the altimeter echo waveforms was also shown to provide an assessment of the laser spot geolocation. Although the accuracy of this technique is not equal to the other methodologies, it does offer position determination for comparison to the spacecraft altimetry data product. In addition, elevation verifications were made using the comparison of the ICESat elevation products at WSSH to those acquired with an airborne light detection and ranging. The elevation comparisons show an agreement to within plusmn34 cm (plusmn6.7 cm under best conditions) which indicate no significant errors associated with the pointing knowledge of the altimeter