The effects of liquid water on the NDSA method for measuring tropospheric water vapor along LEO-LEO satellite links

摘要

The NDSA (Normalized Differential Spectral Absorption) method has been proposed for estimating the total content of water vapor (IWV, Integrated Water Vapor) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites. This method requires a transmitter onboard the first LEO satellite and a receiver onboard the second one. It is based on the simultaneous measurement of the total attenuation at two relatively close frequencies in the Ku/K bands, and on the estimate of a parameter referred to as 'spectral sensitivity'. This approach is potentially able to emphasize the water vapor contribution, to cancel out all spectrally flat unwanted contributions and to limit the impairments due to tropospheric scintillation. The objective of this paper is to analyze the effects of liquid water presence along the propagation LEO-LEO link on the NDSA approach. Results are based on computer simulation and account for different frequency carriers in the 15-30 GHz range and for any value of liquid water content along the propagation path at 3 km tangent altitude.