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Performance of the Shuttle Radar Topography Mission, X-band radar system

The German contribution to the Shuttle Radar Topography Mission (SRTM) is an X-band SAR Interferometer. In 1994 successfully flown flight hardware from the Shuttle radar lab is reused and modified to form a single pass interferometer. The original system is used as the prime channel with the radar transmitter and the channel one receiver. The secondary receive only channel is a new design with an electronically steering antenna beam using existing spare parts like the antenna panels for the 6 meter long array. The steering capability became necessary to compensate for the mast dynamics to keep the prime and secondary antenna beams aligned in azimuth. The performance degradation by using only half of the antenna length compared to the prime channel is recovered by using better low noise amplifiers and by avoiding long corporate feed networks. To optimize the radar parameters special developed software tools are used. Based on a low-resolution backscatter and height map from the Earth, the gain settings and the receiver window presettings are calculated and monitored real-time. This paper describes the X-SAR instrument monitoring concept and reports about the performance, the experience and results from the SRTM mission early this year.