Abstract
GaoFen-3, the first polarimetric SAR satellite of China, carried out polarimetric calibration experiments using C-band polarimetric active radar calibrators (PARCs), trihedral corner reflectors (TCRs), and dihedral corner reflectors (DCRs). The calibration data were firstly processed referring to the classic 2 × 2 receive R and transmit T model for radar polarimeter systems, first proposed by Zebker, Zyl, and Held, and Freeman’s method based on PARCs, but the results were not good enough. After detailed analysis about the GaoFen-3 polarimetric system, we found that the system had some nonlinearity, then a new imbalance parameter was introduced to the classic model, which is equivalent to the γ proposed in Freeman’s paper about a general polarimetric system model. Then, we proposed the calibration data processing algorithm for GaoFen-3 based on the improved model and obtained better results. The algorithm proposed here is verified to be suitable for GaoFen-3 and can be applied to other spaceborne and airborne fully-polarimetric SAR systems.
Highlights
Polarimetric radar has received much attention due to its application advantages
Freeman mentioned a similar situation in [3]; we introduce a new factor, which is equivalent to the γ proposed in the paper, and start from his general polarimetric system model of the 4 × 4 distortion matrix, perform a simple transformation to form an improved 2 × 2 polarimetric system model
Like Freeman’s model (4), the improved model can be applied to many practical polarimetric systems, and many polarimetric calibration methods based on the classic system model could be applicable after the correction of the measured matrix through the γ factor
Summary
Polarimetric radar has received much attention due to its application advantages. In the last three decades, from airborne fully-polarimetric SAR such as NADC/ERIMP-3SAR [1], AIRSAR [1,2,3,4,5,6], CRLNASDASAR [7], EMISAR [8], Pi-SAR/Pi-SAR2 [9,10,11], PolSAR [12], and the Ingara system [13] to spaceborne fully-polarimetric SAR such as SIR-C [14,15,16,17], ALOS-1 [18,19,20,21,22], RadarSat-2 [23,24,25] and ALOS-2 [26,27], many polarimetric SAR systems have been constructed. The validity of the majority of the polarimetric calibration methods in this literature depends on the validity of the system model for radar polarimeters [3], which was first put forward in [37] This system model has a 2 × 2 matrix form and contains just six relative parameters, including four cross-talk terms and two channel imbalance terms. The determination of these six parameters, followed by correction for any deviations from the ideal, is sufficient to calibrate the radar data, so that the HH, HV, VH, and VV scattering matrix measurements can be meaningfully compared [3].
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