【作者】 樊雅文；

【导师】 黄兴友；

【作者基本信息】 南京信息工程大学 ， 大气遥感科学与技术， 2012， 硕士

【摘要】 毫米波雷达由于其较高的时空分辨率,可以用来较精细地研究云结构和云特性。本文利用一部单发双收、兼有多普勒功能的35GHz测云雷达,对几种常见的云型进行观测,在获得一批有代表性资料的基础上,开展了云参数及垂直结构的初步研究。论文的主要内容和结果如下：1)根据反射率因子Z与衰减系数k之间的经验关系,采用分级逐库订正的方法,对2010年7月在广东阳江的遥感探测试验期间获得的个例数据(层状云、降水性层状云、对流云及卷云)进行了衰减订正试验,且将订正后的回波强度与X波段雷达探测资料进行对比,得到衰减订正的初步结果：对于回波较弱的非降水云,订正效果较好；对于降水回波,一方面由于云内液水含量较高,另一方面由于降水及传播路径上的水汽对电磁波的衰减严重,所以订正难度较大,层状云降水回波衰减订正值最大可达10dB。2)当雷达波长λ确定后,球形粒子的散射情况主要取决于粒子直径d和入射波长λ之比。当d<<兄时,为Rayleigh散射,当d≈λ时称为Mie散射。相对于波长为8.6mm的毫米波,直径1.8mm以上的雨滴属于大粒子,不能用Rayleigh散射公式计算其回波强度。大的雨滴粒子在降落过程中会发生形变,复杂的Mie散射公式才能准确计算,因此本文采用离散偶极子近似法(Discrete Dipole Approximation, DDA)计算任意形状“大雨滴”的散射截面,进而订正回波强度,提高了回波的准确性。3)参考国外的毫米波雷达探测与飞机穿云试验得到的公式,利用我校的35GHz地基毫米波测云雷达资料,研究了云内液水含量、冰水含量、云内粒子有效直径,结合外场试验数据,给出了初步反演结果,并根据毫米波雷达的基数据,分析了不同类型云个例的垂直分布情况。4)开发了毫米波雷达数据处理系统,该系统可进行云参数的反演、回波强度的衰减订正、大粒子散射订正。另外,考虑到NetCDF格式的雷达数据在欧美地区广泛性,本数据处理系统也增加了将GLC-34雷达数据转换为NetCDF格式的功能。更多还原

【Abstract】 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.更多还原