Scattering and emissivity of rain events using boundary element method
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The theory of thermal microwave emission from a bounded medium containing random nonspherical discrete scatters is studied. It is known that for a medium of constant temperature the emissivities can be related to the bistatic scattering coefficients. Such relations hold for the four Stokes parameters. The down-welling polarimetric emission of the rain can be computed by means of the radiative transfer equation, which contains the four Stokes parameters. In order to apply the above equation to a realistic rain event, raindrop shapes have to be taken into account in the computation of the scattering amplitudes. Those shapes were obtained by Pruppacher and Pitter and are quite different from a sphere when the size increases. In this paper a procedure based in the Boundary Element Method (B.E.M.) is presented to compute the scattering amplitudes for each drop shape. Results are then averaged for all drop radii with a weighting function given by the Laws-Parson law. This law establishes the relationship between the drop size distribution and the rain intensity. A Gaussian distribution of the drop canting angle due to the wind has been also considered. Finally, some numerical results are presented. The scenario consists of a rain cell of 4 Km height at a uniform temperature, considering the wind effect. The values of the rain intensity and wind speed and direction have been obtained from realistic measurements recorded by a meteorological station located in campus. In order to validate these results, the four Stokes parameters obtained with these simulations were compared with the ones measured by a X-band polarimetric radiometer developed in our laboratory.
CitacióDuffo, N., Vall-llossera, M., Camps, A., Corbella, I., Bara, F., Torres, F. Scattering and emissivity of rain events using boundary element method. A: International Conference on Computational Plasticity. "ECCOMAS 2000: European Congress on Computational Methods in Applied Sciences and Engineering: Barcelona: 11 - 14 September 2000; incorporating the VI International Conference on Computational Plasticity (COMPLAS VI)". Barcelona: 2000, p. 1-13.
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