Multi-band NDSA measurements between two counter-rotating LEO satellites for estimating the tropospheric water vapor profile

NDSA (Normalized Differential Spectral Absorption) was proposed as a differential attenuation measurement method to estimate the total content of water vapor (IWV, Integrated Water Vapor) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites during a relative occultation event. The NDSA approach is based on the estimate of a “spectral sensitivity parameter” that can be directly converted into IWV through empirical relationships In this paper we present the multi-band approach to convert the five simultaneous K_u, K and M spectral sensitivity measurements (17, 19, 21, 179 and 182 GHz) into an integrated water vapor profile up to 14 km tangent altitude. The algorithm is based on the estimate of the SNR (Signal to Noise Ratio) at the receiver, so as to exploit adaptively at every tangent altitude the optimal channel, based on actual signal conditions.