In the past decades FGAN's Tracking and Imaging Radar (TIRA) has been the most accuracy requirements demand for better calibration work. So far efforts suffer from absence of reference data to find out absolute offsets. DORIS system aboard French stellites SPOT-2 and SPOT-4 provides precise position data by Doppler frequency measurements with the help of a worldwide ground-station-network. In cooperation with DGA, France, several representative satellite passages were tracked by TIRA in January 2001. DORIS data of the same timeframe were used as position reference data to determine absolute bias in azimuth, elevation and range. Furthermore the statistical spread of TIRA data was analyzed for S/N-dependency to allow fast quality control. So far the calculated absolute biases were examined partly in dependence on their origin and their influence on quality of TLE-sets generated in-house.