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22 December 2004 Backscattering enhancement with a finite beam width for millimeter-wavelength weather radars
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Backscattering enhancement from random hydrometeors should increase as wavelengths of radars reach millimeter regions. For 95 GHz radars, the reflectivity of backscattering is expected to increase by 2 dB, due to multiple scattering including backscattering enhancement, for water droplets of diameter of 1 mm with a density of 5 x 103 m-3. Previous theoretical studies of backscattering enhancement considered infinitely extending plane waves. In this paper, we expand the theory to spherical waves with a Gaussian antenna pattern, including depolarizing effects. While the differences from the plane wave results are not great when the optical thickness is small, as the latter increases the differences become significant, and essentially depend on the ratio of radar footprint radius to the mean free path of hydrometeors. In this regime, for a radar footprint that is smaller than the mean free path, the backscattering-enhancement reflectivity corresponding to spherical waves is significantly less pronounced than in the case of the plane wave theory. Hence this reduction factor must be taken into account when analyzing radar reflectivity factors for use in remote sensing applications.
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Satoru Kobayashi, Simone Tanelli, Toshio Iguchi, and Eastwood Im "Backscattering enhancement with a finite beam width for millimeter-wavelength weather radars", Proc. SPIE 5654, Microwave Remote Sensing of the Atmosphere and Environment IV, (22 December 2004);

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