Abstract
At frequencies below 10 GHz, the scattering crosssection of raindrops is small compared with the absorption cross-section and the multiple scattering effect is negligibly small. At higher frequencies, however, the scattering cross-section becomes comparable to the absorption cross-section, and some multiple scattering effects may be observed. This paper presents a study of the multiple scattering effects, and the resulting incoherent intensity for a plane wave incident upon a plane-parallel rain region. General formulations of the equation of transfer using Stokes’parameters are given, and the extinction matrix is introduced which take into account the depolarization effects and the nonspherical shape of raindroplets. The calculations are made for the spherical droplet case. It is assumed that a circularly-polarized wave is normally incident upon a plane-parallel rain medium. The scattering characteristics are calculated using the Mie solution and the Laws-Parsons distributions. The calculation of the incoherent intensities are made using the matrix eigenvalue technique. The exact solutions are compared with the first-order scattering solution to estimate the range of validity of the first-order theory. The ratio of the incoherent to the coherent received powers are calculated at 30 GHz, for rain rates of 12.5, 50, 100, and 150 mm/h, rain thicknesses of 3 km and 10 km, and fields-of-view of 1, 5, and 15 deg.
Analyse
Aux fréquences inférieures à 10 GHz, la section efficace de diffusion des gouttes d’eau est faible en comparaison de la section efficace d’absorption et l’effet de diffusion multiple est négligeable. Aux fréquences supérieures, la section efficace de diffusion devient comparable à la section efficace d’absorption et quelques effets de diffusion multiple peuvent être observés. Ceux-ci sont étudiés dans l’article ainsi que l’intensité incohérente résultante pour une onde incidente plane sur un plan parallèle à la zone pluvieuse. Les auteurs donnent les formules générales de l’équation de transfert utilisant les paramètres de Stokes et présentent la matrice d’extinction en tenant compte des effets de dépolarisation et de la non-sphéricité des gouttes. Dans le cas de gouttes sphériques et d’une onde polarisée circulairement et incidente perpendiculairement à un plan parallèle à la zone pluvieuse, les caractéristiques de diffusion sont calculées un utilisant la solution de Mie et la distribution de Laws et Parson. Le calcul des intensités incohérentes est fait par la méthode de la valeur propre des matrices. Les solutions exactes sont comparées à celles de la diffusion du premier ordre pour estimer le domaine de validité de la théorie du premier ordre. Les quotients des puissances reçues incohérentes et cohérentes sont calculés à 30 GHz pour des intensités de précipitations de 12,5, 50, 100 et 150 mm/h, des épaisseurs de pluie de 3 et 10 km, et des ouvertures de champ de 1,5 et 15 deg.
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Ishimaru, A., Cheung, R.L.T. Multiple scattering effects on wave propagation due to rain. Ann. Télécommunic. 35, 373–379 (1980). https://doi.org/10.1007/BF03003515
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DOI: https://doi.org/10.1007/BF03003515