On the use of transponder measurements for high precision assessment and calibration of polarimetric Radarsat-2

An independent assessment and calibration of polarimetric RADARSAT-2 (RS2) are conducted using transponder measurements extracted 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 crosschannel relative phase correction is required to provide calibrated data that meet comfortably the CEOS Cal-Val requirements. To take full advantage of the excellent RS2 performance in terms of low noise floor (-38 dB), transponder measurements are used for high precision assessment of RS2 calibration parameters. It is shown that the antenna cross-talks are stable with incidence angle, and only one transmitter-receiver distortion matrix is required for accurate calibration of the 20 modes of RS2 (Right looking) from 20° to 40°. A new method based on high precision transponder measurements is introduced for polarimetric RS2 calibration. Data collected at various incidence angles are used to validate the calibration. Transponder measurements using calibrated data indicate a residual cross-talk lower than -43 dB. The residual cross-channel error is lower than 0.3 dB in radiometry, and 5° in phase.