Global simulation of tropospheric water vapor measurements through the Normalized Differential Spectral Attenuation (NDSA) approach: setup, scintillation model and performance evaluation

NDSA (Normalized Differential Spectral Absorption) was recently 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 set/rise (occultation) event. The NDSA approach is based on the simultaneous estimate of the total attenuations at two relatively close frequencies and of a "spectral sensitivity parameter" that can be directly converted into IWV through empirical relationships that can be previously derived based on statistical regressions between spectral sensitivity and IWV simulated through real radiosonde data and a propagation model. In this paper we present the error performance in the IWV profile retrievals in the troposphere (up to 14 km) on the basis of an entire day of occultation events in a ECMWF-model simulated atmosphere. For the first time, we present results of simulations of NDSA measurements made in the millimeter band (in addition to the Ku/K bands analysed in previous works), specifically at 179 and 182 GHz. © 2009 SPIE