Multiple scattering calculations of rain effects

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Abstract
At millimeter wave frequencies the scattering cross section of raindrops becomes comparable to the absorption cross section, and incoherent intensity due to multiple scattering may become significant. This paper presents calculations of the incoherent intensity at 30, 60, 90, and 120 GHz. The scattering and absorption characteristics of the rain are calculated using the Mie solution and the Laws‐Parsons distribution. Incoherent intensities for the horizontal and vertical polarizations are obtained using the equation of transfer and the Stokes parameters. The obliquely incident wave is linearly polarized. The equation of transfer is solved by using the Gauss quadrature formula and the matrix eigenvalue technique. The matrix elements are calculated using the formulations developed by Sekera, and the vertical and horizontal components and their correlations are used in the Stokes parameter representations. The received incoherent intensity depends on the field of view of the receiving antenna. The ratio of the copolarized incoherent intensity to the copolarized coherent intensity is defined as the incoherent copolarized discrimination I‐CPD, and the ratio of the cross‐polarized incoherent intensity to the copolarized coherent intensity is defined as the incoherent cross‐polarized discrimination I‐XPD. These are computed in terms of rain rate, field of view, and copolarized attenuation. It is shown that multiple scattering effects may become significant during heavy rains. Backscattering results are also presented.