Pointing angle and timing calibration/validation of the Geoscience Laser Altimeter with a ground-based detection system

The scientific goals of the laser altimeter carried on ICES at require that the laser pointing direction should be known to an accuracy of 1.5 arcseconds and the time tag of the altitude measurement should have an accuracy of 0.1 millisecond. In order to verify that the satellite altimetry instrumentation is properly characterized, the laser spot position and time tag should be independently verified. One independent approach uses a ground-based electro-optical detector array. Operation of many devices over an area will enable detection of the laser footprints when they illuminate the ground. With the coordinates of the captured spot obtained from the detector array, the laser spot position determination is compared to the position inferred from the data collected onboard ICESat. A small subset of these detectors will also be used to time-tag the footprint for further verification. These timing detectors will be hardwired to a central timing station that uses a GPS receiver to time stamp the laser pulse time of arrival. The detectors used only for positioning are designed for autonomous operation