Generalized Parametric Prediction Model of the Mean Radiative Temperature for Microwave Slant Paths in All-Weather Condition

The mean radiative temperature (T_mr) is a key function controlling the sky noise temperature in microwave receiving systems. A generalized parametric prediction (GPP) model of T_mr for microwave slant paths in all-weather conditions is formulated and presented. The proposed GPP model is aimed at being multifrequency and surface-temperature scaled, valid for elevation angles from 5° to 90° and for frequencies ranging from 5 to 95 GHz within the three transmission windows delimited by the water vapor and the oxygen absorption peaks. The core of the GPP model is a parametrization driven by a physically based radiative transfer approach taking into account extinction, emission, and multiple scattering. The expression of T_mr is normalized to the surface temperature of the considered site. The GPP model is verified with measurements available from the multi-instrument Italian Satellite (ITALSAT) campaign in Spino d'Adda, Milan, Italy, in 1994-1997, obtaining a fractional mean error ranging from 0.045 to 0.068. A comparison of the GPP model with the current ITU-R model shows a reduction in the root mean square error up to about 20 and 30 K, depending on the considered frequency.