Calibration of Dual Polarimetric C-BAND SAR data: a possible approach for SENTINEL-1
Marco Lavalle(1), Domenico Solimini(1), Betlem Rosich(2) and Eric Pottier(3)
(1) University Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy
(2) ESA-ESRIN, Via Galileo Galilei 1, 00144 Frascati, Italy
(3) University Rennes 1, 263 Avenue General Leclerc, 35042 Rennes, France
In this paper we discuss the radiometric calibration of dual polarimetric Synthetic Aperture Radar (SAR) data. A dual polarimetric system transmits the same polarized wave at each pulse repetition frequency and receives coherently on both polarimetric channels H and V. Nowadays, ALOS-PALSAR and RADARSAT-2 can operates a dual-pol mode, and the future ESA mission Sentinel-1 will carry on-board a dual polarimetric C-band SAR sensor. We focus on the calibration of a C-band SAR system that transmits in linear polarization and receives on H and V (i.e. the two modes HH/HV and VV/VH) like Sentinel-1.
The calibration of dual-pol data for those sensors that can operate also in quad-pol mode, such as PALSAR and RADARSAT-2, can be achieved by assuming that the system characteristics do not change from dual-pol to quad-pol acquisitions. On this way, the calibration of the HH/HV mode data (or VV/VH mode data) is performed using the same receiving distortion matrix estimated from quad-pol data. However, when the SAR sensor operates only a single- and a dual-pol mode, as in the case of Sentinel-1, the polarimetric calibration procedure must be adapted and the calibration parameters must be estimated using dual-pol data.
We have derived a distortion model for dual-pol data using the approach in . The polarimetric distortion model of dual-pol SAR includes four calibration complex parameters: the cross-talk on transmit, the receiving channel imbalance and two receiving cross-talks. We have studied the response of particular targets according to this distortion model. We show that the polarimetric calibration of a dual-pol acquisition mode is possible using a trihedral-like and an oriented dihedral-like response inside the SAR scene, plus a distributed target having azimuthal symmetry. The reciprocity assumption between transmission and reception is not needed. In the proposed calibration procedure, Faraday rotation can be estimated from external data and applied as further step. We finally discuss the calibration procedure as possible approach for Sentinel-1 data.
S. Quegan, "A unified algorithm for phase and cross-talk calibration of polarimetric data-theory and observations," Geoscience and Remote Sensing, IEEE Transactions on, vol. 32, no. 1, pp. 89–99, Jan 1994.