A high accuracy calibration and receive instrument for TerraSAR-X ground calibration Rainer Lenz, Juan Pontes, Werner Wiesbeck Universität Karlsruhe (TH) Institut für Höchstfrequenztechnik und Elektronik Kaiserstrasse 12 76 131 Karlsruhe, Germany rainer.lenz@ihe.uka.de Abstract — TerraSAR-X is a new earth observing satellite which will be launched in spring 2006. It carries a high resolution X-band SAR sensor. For high image data quality, accurate ground calibration targets are necessary. This paper describes a novel system concept for an active and highly integrated, digitally controlled SAR system calibrator. A total of 16 active transponder and receiver systems and 17 receiver only systems will be fabricated for a calibration campaign. The calibration units serve for absolute radiometric calibration of the SAR image data. Additionally, they are equipped with an extra receiver path for two dimensional satellite antenna pattern recognition. The calibrator is monitored by a dedicated digital control unit. For antenna pattern estimation, an algorithm is presented. I. INTRODUCTION The radar instrument in the TerraSAR-X satellite works in X-band at a center frequency of 9.65 GHz. Its nominal bandwidth is 150 MHz. The satellite can also operate in an experimental mode with an extended bandwidth of 300 MHz. The satellite will provide high quality data for various kinds of application, e.g. vegetation, security, oceanography. The SAR instrument is highly versatile by implementing multiple operation modes adapted to the desired applications. The SAR data will be available for the scientific community as well as for commercial use. In order to guarantee high data accuracy and verify the data quality, both internal and external calibration is necessary. Internal calibration is more related to the SAR instrument itself and not topic of this paper. External calibration measures the response of known radar targets and allows to derive data correction coefficients. External calibration can be done by purely passive targets. The lower the frequency the larger the passive targets’ geometric size is. In X-band, a passive triple corner reflector for a radar cross section of 50 dBsm demands an edge length of 2.14 m. With the advance of MMIC technology and low cost digital control systems, active radar calibration even at X-band becomes promising. Active radar calibrators cannot only yield one fixed radar cross section (RCS) but they are multifunctional. The RCS value can be adjusted, radar signal analysis can be performed and signal detection of the satellite becomes possible. This digitally Figure 1: Block Diagram of transponder system with digital control unit