| An improved model for the microwave brightness temperature seen from space over calm ocean is presented. This model can be divided into two sub-models, the atmospheric absorption model and the ocean surface emissivity model.; An improved model for the absorption of the atmosphere near the 22 GHz water vapor line is presented in the first part of this work. The Van-Vleck-Weisskopf line shape is used with a simple parameterized version of the model from Liebe for the water vapor absorption spectra and a scaling of the model from Rosenkranz for the 20-32 GHz oxygen absorption. Radiometric brightness temperature measurements from two sites of contrasting climatological properties--San Diego, CA and West Palm Beach, FL--are used as ground truth for comparison with in situ radiosonde derived brightness temperatures. Estimation of the new model's four parameters, related to water vapor line strength, line width and continuum absorption, and far-wing oxygen absorption, are performed using the Newton-Raphson inversion method. Improvements to the water vapor line strength and line width parameters are found to be statistically significant. The accuracy of brightness temperatures computed using the improved model is 1.3-2% near 22 GHz.; In the second part of this work, a modified ocean emissivity model is presented. We investigate the contribution to the brightness temperature from the specular ocean emission. For this purpose, satellite-based microwave radiometric measurements from the TOPEX/Poseidon project are employed together with near-coincident radiosonde profiles from fifteen stations around the world's oceans and TOPEX altimeter measurements for filtering of low wind conditions. The radiative transfer equation is applied to these profiles, using the atmospheric model developed in part one, in order to account for atmospheric effects in the modeled brightness temperature. NODC ocean temperature and salinity profiles are used in determining the dielectric properties of sea water. The ocean complex permittivity model developed by Klein and Swift and, more recently, by Ellison is tested and revised. The average error in the modified ocean emissivity model, over the range 18-40 GHz, is found to be 0.0037, which in terms of brightness temperatures, translates to a model error of approximately 1K. |
