Improving the Accuracy in Predicting Water-Vapor Attenuation at Millimeter-Wave for Earth-Space Applications

This contribution focuses on improving the accuracy of the simplified method currently recommended by the ITU-R for the prediction of water-vapor attenuation at millimeter-wave on Earth-space links (Annex 2, paragraph 2.3 of recommendation ITU-R P.676-10), which receives as input only the local integrated water-vapor content V. The main improvement to such model originates from taking into account the dependence of the water-vapor mass absorption coefficient aV on the reference site altitude, which is investigated by taking advantage of an extensive set of radiosonde observations (RAOBS) collected in several sites worldwide and characterized by high accuracy and reliability. Tested against attenuation estimates obtained from the mass absorption models coupled with the mentioned RAOBS data, the model's prediction accuracy turns out to improve significantly with respect to the current recommendation and to be less dependent both on the operational frequency (20-100 GHz range) and on the considered site.