Global mapping of attenuation at Ku- and Ka-band

The propagation of radio waves for Earth-space slant path at C-band and higher frequencies is 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 Tropical Rainfall Measuring Mission (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 microphysical model for precipitation developed using hydrometeor size distributions and thermodynamic phase state is used to estimate attenuation and reflectivity observations at 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). Differences in the microphysical structure in convective and stratiform precipitation are also incorporated in the model. The results show substantial attenuation variation in a 12-month period at both Ku- and Ka-bands over the various regions of the globe, including the contrast between land and ocean. The estimates of attenuation made at Ku- and Ka-band will be useful in the design and development of spaceborne systems.