Global mapping of attenuation at X-band and higher frequencies

The propagation of radio waves for Earth/space slant path at C-band and higher frequencies are dominated by precipitation in the atmosphere. At a given frequency, attenuation depends on the length of the radio path, the size distribution and the phase state of the hydrometeor profile. Using the observations from the TRMM spaceborne Ku-band (13.8 GHz) radar at Low Earth Orbit of 350 km above Earth, global attenuation maps are produced at the Ku-band frequency. A simple precipitation microphysical model developed using hydrometeor size distributions and phase state is used to scale this observed attenuation to Ka-band (35 GHz) where numerous high bandwidth satellite applications are being planned including the next generation space based radar for the Global Precipitation Mission (GPM). In this study, three layers of precipitation that consist of aggregate, dry graupel and rain are considered. Using this precipitation model the attenuation and backscatter reflectivity relations between Ka- and Ku-band frequencies are developed for scaling the specific attenuation and backscatter reflectivity along the observation path. The results show substantial attenuation variation in a 12-month period at both Ku- and Ka-bands over the various regions of the globe. These results can help in the design and development criteria for satellite applications at Ka-band.