CLOUD EFFECTS ON THE NDSA MEASUREMENTS FOR WATER VAPOR ESTIMATE IN THE LOWEST TROPOSPHERE BY LEO-LEO SATELLITES IN THE 10-30 GHz RANGE

摘要

A differential measurement concept for retrieving the total content of water vapor (IWV, Integrated Water Vapor) along the propagation path between two Low Earth Orbiting (LEO) satellites was proposed by the authors some year ago. The concept is based on the simultaneous measurement of the total attenuation at two relatively close frequencies in the 17-21 GHz range, and on the estimate of the NDSA (Normalized Differential Spectral Absorption) parameter. Such parameter provides directly the IWV content along the LEO-LEO link in case of dry air atmospheric conditions (no liquid water along the propagation path). In this paper we analyze the effects of liquid and solid water on NDSA measurements and how such effects must be accounted for in converting NDSA measurements in IWV. We quantify the effects of liquid water on NDSA measurements in the 10-30 GHz range. We show how NDSA at 30 GHz can be used to check the presence of liquid water and how liquid water influence the conversion in IWV at 17, 19 and 21 GHz. Finally we discuss the possibility to use the NDSA at 30 GHz for estimating directly the liquid water content along the propagation path as well as we propose the conversion of NDSA to IWV in the 17-21 GHz range.