Study On Radiowave Propagation Characteristics And Remote Sensing Of Hydrometeors

Hydrometeors have dominant effect on the performance of systems operating at frequencies above lOGHz, and the remote sensing of hydrometeors is an important subject for radio propagation, radar meteorology and atmosphere physics etc. Based on the physics characteristics of rainfall, fog and clouds, the propagation characteristics and remote sensing of hydrometeors are investigated and discussed. The main contributions of author's work are as follows:Based on the measured data of rain drop size distribution (DSD), the average rain DSD models in Qingdao, Guangzhou and Xinxiang are obtained. Using the DSD models and forward scattering amplitude computed by the least squares fitting method, the specific attenuations at l-400GHz have been computed and analyzed, the parameters of "power law" relation between specific attenuation and rainfall rate are obtained. The specific attenuations in Qingdao, Guangzhou and Xinxiang are compared with ITU-R specific rain attenuation models. The analytic specific attenuation model for rain for use in prediction methods are developed, the specific rain attenuations calculated by the analytic model are in high agreement with those by the parameters tabulated in ITU-R model, this model has presented to ITU-R as a proposed revision to current ITU-R model. The prediction methods of rain attenuation for design of terrestrial and earth-space systems are also introduced.Based on the theory of rain-induced rain-induced cross-polarization discrimination (XPD), the two-order small argument approximation for rain-induced XPD is developed, and a new model for predicting rain-induced XPD is proposed based on this approximation. The comparisons of this new model with other models and experiments data show that some improvement has been obtained with this model, especially for different polarizations.Based on rain drop size distribution (DSD)data measured in Qingdao, Guangzhou and Xinxiang, the radar reflectivity factor Z for spherical rain drops, the radar reflectivity factor ZH and differential reflectivity ZDR for oblate ellipsoid rain drops have been calculated. The relation of reflectivity and rainfall rate for conventional meteorological radar and the relation of reflectivity, differential reflectivity and rainfall rate for multiparameter radar are regressed , The performance difference of two kinds of radar for measuring rainfall and difference for measuring rainfall in different regions are also discussed.Based on the liquid water content and optical visibility, the method for determining the parameters of gamma drop size distribution model of fog and clouds are developed, the drop size distributions for advection and radiation fog are obtained with empirical relations of the liquid water content and the visibility, the characteristics of drop size distribution for different kinds of fog are analyzed and discussed. A new empirical formula to estimate fog and clouds attenuation is developed based on the Reyleigh absorption approximation, which is more accurate in general and can be used in wider frequency and temperature range than other empirical formulas. The attenuation are also calculated and discussed with fog drop size distribution model and empirical relations of the liquid water content and the visibility or other parameters of fog and clouds. The measured results of sea fog attenuation in Qingdao at 33.5GHz and 93.5GHz are analyzed and discussed.The fog attenuations at infrared wavelength are computed and analyzed with the fog drop size distribution model of radiation and advection fog, the empirical relation of fog attenuation with water content or visibility are obtained at 10.6 urn wavelength, the relation for radiation fog have a good agreement with the relation obtained by experimental results. Based on the fog drop size distribution model of radiation and advection fog, the backscattering characteristics of fog have been investigated and the empirical relations of the radar reflectivity factor and water content or visibility are obtained. The method for remot...