Data Quality Assessment of Polarimetric RADARSAT2
Ridha Touzi(1), R.K. Hawkins(1), S Cote(2) and T Luscombe(3)
(1) Canada Centre for Remote Sensing, 588 Booth St.,, Ottawa, Ont. K1A 0Y7, Canada
(2) Canada Space Agency, St Hubert, St Hubert, Canada
(3) MDA, Vancouver, Vancouver, Canada
RADARSAT2 is equipped with polarimetric capability at multiple incidence angles and at fine at standard mode 9 m and 24 m resolution. The phased RADARSAT2 array antenna has been conceived with a requirement on the H-V isolation better than -30 dB. As such, no digital elevation model is required for calibration of areas with significant topographic relief, and this makes RADARSAT2 calibration much easier. In this study, a quality assessment of calibrated polarimetric RADARSAT2 is conducted. A transponder conceived by CSA in collaboration with CCRS  is used for the measurement of the impulse response characteristics, and for the assessment of the accuracy of polarimetric data collected at 25 degree and 40 degree incidence angle. A corner reflector deployed by MDA is also used. The Freeman-Van Zyl calibration technique , which symmetrises the system prior to the estimation of the distortion matrix elements, is adopted. Van-Zyl’s technique  for determination of system distortion matrix elements is reconsidered, and additional equations  are used to optimize the estimation of the calibration system unknowns even when the azimuthally symmetric reference target is of very low HV return in comparison with HH, VV, and the HH-VV cross-correlation. This new calibration method was validated for PALSAR calibration, and permit demonstrating that PALSAR antenna isolation is higher than -35 dB , in contrast to the -25 dB isolation obtained by many studies  using the conventional Van-Zyl algorithm or the Quegan calibration method.
The application of the new calibration method leads to excellent news regarding RADARSAT2 polarimetric calibration accuracy. The calibrated data are highly isolated with antenna cross talks lower than -40 dB. Channel imbalance is also close to 1 with a channel imbalance ratio within 0.2 dB, and phase difference variation less than 2 degree. The transponder permits the demonstration of the high accuracy of inter-channel radiometry and phase; within 0.3 dB in radiometry and 5 degree in phase. Uncalibrated data will also be assessed to demonstrate the excellent isolation of RADARSAT2 antenna.
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