Airborne imaging microwave radiometer. I. Radiometric analysis

Abstract

The airborne imaging microwave radiometer (AIMR) was designed and built for regional scale sea ice mapping. It operates at 37 and 90 GHz (nominal), and collects radiance at two orthogonal polarizations from which one can compute horizontal and vertical polarizations. The sensitivity or precision (/spl Delta/T) of the radiometric data is on the order of 0.5-0.8 K for the 37 GHz channels and 0.8-1.5 for the 90 GHz channels. A detailed error analysis was conducted to assess the accuracy of the radiometric measurements. The error in the brightness temperatures of the original orthogonal polarizations channels was found to be on the order of 0.35-0.45 K for the 37 GHz channel and 0.55-0.65 K for the 90 GHz channel. The polarization conversion introduces additional errors and these are analyzed and computed for the LIMEX-89 data. The total error due to both calibration and polarization conversion for incidence angles greater than 20/spl deg/ is on the order of 0.65-0.70 K for 37 GHz and 0.75-0.85 K for 90 GHz. For incidence angles between 10/spl deg/ and 20/spl deg/ the error can be up to 1.5 K. As the incidence angle approaches zero the distinction between horizontal and vertical polarization breaks down and the error approaches infinity.