PALSAR calibration with passive antenna reflectors
(1) FIRE RAS, Vvedensky square 1, 141190 Fryazino, Russian Federation
The polarimetric mode of PALSAR provides new and unique opportunities in the area of Earth remote sensing, though complicates at the same time SAR equipment calibration tasks. We discuss here radiometric and polarimetric calibration of PALSAR by means of ground-based passive targets - parabolic antennas with disks and diffraction grid in focal area. The series of PALSAR calibration experiments with passive antennas to be discussed cover 2 years interval of activities at Bear Lakes test site in Moscow region, since May 2006 till May 2008.
At our calibration use 3 parabolic antennas 4.7 meters in diameter with 50 m spacing between the antennas. The antennas are reconstructed by means of the insertion of various scatterers (conducting disks and diffraction grid) in the focal area. The antennas demonstrated high ~ 43 dBm2 RCS level and better 1 dB stability, though because of relatively narrow targets pattern some SAR sessions were not successful.
Polarimetric calibration of PALSAR with targets having only two different types of scattering matrix was complicating, though channel imbalances may be estimated correctly. For the fulfillment of the polarimetric calibration we consider two ways of cross-talks estimation. One of them is a use of standard Quegan algorithm. And another one is based on a use of strong natural target in urban area having scattering target with properties complementary to the scattering matrices of targets at the calibration site.
Finally we discuss influence of Faraday rotation effect onto calibration process and propose a way of the rotation extent estimation using circular polarization basis.