The X-SAR/SRTM Project Calibration Phase

Kurzfassung

After a very successful mission in February 2000, more than 3.5 terra bytes of X-SAR data are waiting to get processed to digital terrain models and radar images. The calibration or correction of the deterministic phase errors is of utmost necessity before starting the operational processing of all acquired X-SAR/SRTM SAR data. As expected, the motion variation of the Space Shuttle in orbit and the dynamic oscillation of the mast caused height errors. The basis for the motion compensation in the processor is the position and attitude data record (PADR) which has been derived from the measurements made during the mission by the different sensors of the attitude and orbit determination assembly. Furthermore there are height errors from the radar noise and also systematic height errors originating from the radar instrument itself that need compensation. Temperature instabilities are the major source for these phase variations. Telemetry data were monitored and recorded throughout the mission, they indicated periodic temperature variations along the orbit path, over the course of a data-take and over the 11 days of the mission. The major phase errors were either measured directly, as was done for the long mast cables, or were derived from the calibration tone phase by analysis. With the responses of the deployed corner reflectors at the calibration test sites, the range delay and the radiometric calibration factor has been found. This paper summarizes and updates recent publications about the DLR X-SAR/SRTM calibration activities and shows preliminary results for the height accuracy.