The measure of Water Vapor (WV) in the lower troposphere is a critical issue, which still leaves important margins for improvements of observational data quality, as necessary for instance to enhance the forecast performance of Numerical
Weather Prediction systems. To address this problem, a novel measurement technique for obtaining the Integrated Water Vapor (IWV) along a microwave link and based on a pair of attenuation measurements has been proposed years ago.
This method is called NDSA (Normalized Differential Spectral Attenuation), and is based on measuring the "spectral sensitivity", namely the normalized incremental ratio of the spectral
attenuation, that was found to be linearly related to the IWV along the radio-link path operating in the Ku and K frequency band. The Italian Space Agency (ASI) supported a project named SATCROSS, whose purpose is to provide a prefeasibility study for a different measurement concept, as the number of LEO satellites is higher than two and they are orbiting in the same plane and along the same direction. An instrument prototype operating in a ground-to-ground link
configuration and the development of a measurement campaign. The prototype is an upgrade of a previous one and is designed and implemented to demonstrate the effectiveness of the NDSA measurements at 19 GHz. The results of the first measurements campaign on a ground to ground link and the study for a step forward towards satellite mission are presented here.
