This report gives an overview of microwave radiative transfer modeling in clouds and precipitation. Two model packages are introduced to be made available to the NWP-SAF which are evaluated in part II. Their range of applicability is only limited by the availability of models for the calculation of water and ice permittivity, sea-surface emissivity, and atmospheric absorbtion. Current models for these ingredients are taken to be valid for the frequency intervals 1-100 GHz, and 1-1000 GHz, respectively. The solution to the radiative transfer equation, however, is general and applies to all wavelengths at which contributions from solar radiation can be neglected, i.e., for which the radiation source terms are only diffuse scattering and thermal radiation. The model package includes pre-calculated tables containing the optical properties of hydrometeors at all microwave frequencies currently available on spacebourne sensors.
}, year = {2004}, month = {2004}, language = {eng}, }