High Precision Assessment and Calibration of Polarimetric RADARSAT-2 Using Transponder Measurements

Independent assessment and calibration of polarimetric RADARSAT-2 (RS2) are conducted using transponder measurements from uncalibrated data collected at various incidence angles between 20° and 40°. It is shown that RS2 antenna is highly isolated (better than -32 dB), and only cross-channel relative phase correction is required to provide calibrated data that meet comfortably the CEOS Cal-Val requirements. Given the low noise level (-35 dB in βº), calibration may be improved using high precision cross-talk measurements using a transponder. A new calibration method based on transponder measurements is introduced. Transponder mesurements at incidence angles between 20° to 40° show that the antenna cross-talk is stable with incidence angle, and only one transmitter-receiver distortion matrix may be required for accurate calibration of the 20 polarimetric modes of RS2 (Right looking) from 20° to 40°. The new transponder calibration method removes almost completely the low antenna cross-talk with a residual cross-talk lower than -43 dB. MDA calibration is also assessed for certain modes using the high precision transponder measurements. It is shown that all the mode analyzed meet the CEOS Cal-Val requirements with a residual cross-talk varying between -32 dB and -43 dB, depending on the mode (incidence angle). Data symmetrization significantly improves data quality; the residual cross-talk is lower than -37 dB for all the modes considered, and the signal to noise ratio (S/N) is improved of 3 dB.