Abstract
NASA launched its Ice, Cloud and Land Elevation Satellite (ICESat) in January 2003. Theprimary goal of this laser altimeter mission is to provide determination of volumetricchanges in the ice sheets, specifically in Antarctica and Greenland. The instrumentperformance requirements are driven by the scientific goal of determining a change inelevation on the centimetre level over the course of a year’s time. One important aspect ofthe altimeter data is the time of measurement, or bounce time, associated with each lasershot, as it is an important factor that assists in revealing the temporal changes inthe surface (land/ice/sea) characteristics. In order to provide verification thatthe laser bounce time is accurately being determined, a ground-based detectorsystem has been developed. The ground-based system methodology time-tags thearrival of the transmitted photons on the surface of the Earth with an accuracy of0.1 ms. The timing software and hardware that will be used in the ground-basedsystem has been developed and extensively tested. One particular test utilized anairborne laser equipped to produce a similar signal to that of ICESat. The overflightof the detectors by the aircraft was successful in that the signals were detectedby the electro-optical devices and appropriately time-tagged with the timinghardware/software. There are many calibration and validation activities planned with theintention to help resolve the validity of the ICESat data, but pre-launch analysissuggests the ground-based system will provide the most accurate recovery of timingbias.
Published Version
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