The Correction And Application Studying Of Cloud Radar Data

By providing base data with high spatio-temporal resolution, millimeter wave cloud measurement radar is good research facility for cloud property and structure. A35GHz dopplerized cloud radar with one-transmitter-and-two-polarization-receiver, is used to observe some typical clouds. With the collected cloud echo base data, preliminary works on cloud variable and cloud structure have been implemented. Main works are as following.(1) Regarded to the empirical relationship between reflectivity factor Z and attenuation coefficient k, a bin-by-bin correction method was used to complement the attenuation due to different clouds like stratus clouds, precipitating stratus, convective cloud and cirrus. By comparing the radar reflectivity factors collected by both cloud radar and almost same site X-band radar, the attenuation correction was found of importance and acceptable. The results show that, in cases of cirrus and stratues clouds with weak echo, the corrections are minor and these echoes are almost right. And in case of rainfall, both water droplets and rich water vapor along the ray path cause strong attenuation, and the correction is hard to compensate the attenuation. The largest correction value for preicipitating stratus cloud echo can reach to lOdB.(2) When the wavelength of incident wave is known, scattering of spherical particles is determined by the ratio of d (the diameter of particle) to λ (wavelength). If d<<λ. it calls Rayleigh scattering, if d≈λ, it calls Mie scattering. Relative to8.6mm wavelength, rain droplet with diameter bigger than1.8mm is considerably large, falls into the Mie scattering regime. Shape of the large droplets will be changed when they are falling down, using Mie theory to calculate scattering cross section would be very complicated. So DDA method is employed here for calculating the difference between the two scatterings for a large droplet. After Mie-to-Rayleigh Scattering correction, the cloud radar data is more reliable.(3) Based on empirical relationships from radar and flight experiments, cloud liquid water content and cloud ice water content were retrieved from a35GHz cloud radar measurement, as well as equivalent diameter of cloud droplets. Some results were pointed out. Vertical structure of some different clouds were also analyzed completely based on millimeter wave-cloud radar data.(4) A special data processing system was developed. It is capable of retrieving cloud variables, correcting radar reflectivity factor due to attenuation and Mie scattering caused by some large particles. Besides, regarding to NetCDF data format which is popular in Europe and America, data in GLC-34format can be saved in the form corresponding to NetCDF format.