Calibration of polarimetric radar images using only image parameters and trihedral corner reflector responses

A technique that uses the radar return from natural targets and at least one trihedral corner reflector to calibrate compressed polarimetric radar data is described. Calibration for relative amplitude, relative phase, absolute amplitude, and system crosstalk is addressed. The crosstalk calibration method is based on the theoretical result that for natural targets with azimuthal symmetry the copolarized and crosspolarized components of the scattering matrix are uncorrelated, and the method does not require any external calibration targets to be deployed before imaging. Because compressed data are used, one is forced to model the transmitting and receiving systems as reciprocal. Even though the inferred transmit and receive matrices are not each simply related to the physical transmitter and receiver, the true Stokes matrix for each pixel in an image can be accurately determined by this approach. The method is illustrated by estimating the crosstalk parameters of the NASA/JPL aircraft for different types of terrain and for two frequencies. For the C-band system, the crosstalk is less than -20 dB for all ranges in the images. The crosstalk of the L-band system is a function of range, however, and may be as poor as -10 dB in the near range, leading to a noticeable distortion of the polarization signatures.<
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