A calibration method for fully polarimetric microwave radiometers

Abstract

Abstract-A technique for absolute end-to-end calibration of a fully polarimetric microwave radiometer is presented. The technique is based on the tripolarimetric calibration technique of Gasiewski and Kunkee, but is extended to provide a means of calibrating all four Stokes parameters. The extension is facilitated using a biaxial phase-retarding microwave plate to provide a precisely known fourth Stokes signal from the Gasiewski-Kunkee (GK) linearly polarized standard. The relations needed to determine the Stokes vector produced by the augmented standard are presented, and the effects of nonidealities in the various components are discussed. The application of the extended standard to determining the complete set of radiometer constants (the calibration matrix elements) for the National Oceanic and Atmospheric Administration Polarimetric Scanning Radiometer in a laboratory environment is illustrated. A calibration matrix inversion technique and error analysis are described, as well. The uncertainties associated with practical implementation of the fully polarimetric standard for spaceborne wind vector measurements are discussed relative to error thresholds anticipated for wind vector retrieval from the U.S. National Polar-Orbiting Environmental Satellite System.

Analysys and verification of calibration methods for fully polarimetric W-band radiometer

“…From the experiment results, several characteristics of the proposed fully polarimetric calibration were found. From the results, all performance of our work is better than that of [1] except for the mixing from the polarimetric channels into the orthogonal channel. The mixing from the third Stokes parameter into the orthogonal channel had -18 dB to -25 dB; however, the mixing from the fourth Stokes parameter had poor interference characteristics.…”

“…Only a few calibration performances were reported because the methodology for the fully polarimetric calibration standard was developed recently. In [1], they used the line pattern on the microwave substrate for the wire grid for the fully polarimetric calibration. It's characteristics of grid was supposed to that of ideal grid from the estimation of a priori Stokes vectors at 10.7 GHz.…”

“…In [1], only a dielectric sheet without grid lines was possible to calibrate the first three Stokes parameters for a small dynamic range. However, it has not been reported that the fully polarimetric calibration is possible or not.…”

“…A printed grid on microwave substrate is applied for the polarizing grid. The fist approach of this method was introduced at 10.7 GHz [1]. The grid on a substrate was suggested to have an equal characteristic with a metal grid at operation frequency.…”

A new space technology for ocean observation: the SMOS mission

“…It measures sequentially all four Stokes parameters (see e.g. Lahtinen et al 2003 for the definition) by taking advantage of a specially designed switching schema (Martín-Neira et al 2002). The availability of the full Stokes vector from SMOS is being used to improve the knowledge of the Faraday rotation induced by the ionosphere and also other applications related to measuring winds over the ocean.…”