Potential of combined spaceborne infrared and microwave radiometry for near real-time rainfall attenuation monitoring along earth-satellite links

The objective of this paper is to investigate how spaceborne remote sensors, and their derived products, can be exploited to optimize the performances of a satellite communication system in the presence of precipitating clouds along the path. The complementarity between sun-synchronous microwave (MW) and geostationary infrared (IR) radiometry for monitoring the earth's atmosphere is discussed and their potential as a rain detection system within near real-time countermeasure techniques for earth-satellite microwave links is analysed. A general approach, consisting in estimating rainfall intensity and attenuation by polar-orbiting microwave radiometers and temporally tracking the rainfall areas by geo-stationary infrared radiometers, is delineated. Multiple regression algorithms for predicting rainfall attenuation from spaceborne brightness temperatures and from surface rainrate, trained by radiative transfer and cloud models, are illustrated. A maximum likelihood technique is delineated to discriminate stratiform and convective rainfall from spaceborne brightness temperatures. The di!erences among attenuation estimates derived from layered raining-cloud structures with respect to those obtained from simple rain slabs, as recommended by ITU-R, are also quanti"ed. A test of the proposed attenuation prediction methods is performed using raingage and Italsat data acquired in Spino d'Adda (Italy) during 1994. A description of the statistical method, based on the probability matching technique, adopted to combine MW and IR data for retrieving and tracking precipitating cloud systems in terms of path attenuation and accumulated rain at ground is "nally provided together with its application to a case study over the Mediterranean area during October 1998.