THE GRIDDED TRIHEDRAL - A NEW POLARIMETRIC SAR CALIBRATION REFLECTOR

The calibration of a polarimetric SAR system is achieved through use of radar reflectors with a significant cross-polarized reflection of known properties. Three such reflectors are the dihedral, the active radar calibrator (ARC), and the gridded trihedral. Each of these devices has been used as calibration radar reflectors for the three-frequency (1.25, 5.30, and 9.35 GHz) ERIM/NADC P-3 SAR System. The focus of this paper is on the characteristics of the gridded trihedral. The gridded trihedral is a normal trihedral with one of the conducting faces replaced with a grid of closely spaced (relative to a wavelength) parallel conductors over a layer of microwave absorber. This grid changes the incident wave's polarization and results in a calibration target with a significant cross-polarized reflection. The advantages of the gridded trihedral are that it has a broad backscatter beamwidth (unlike the dihedral), and that it is passive and simple to construct (unlike the ARC). The performance characteristics of the gridded trihedral reflector will be reviewed using basic theoretical models and calibrated P-3 SAR imagery.