星载太赫兹双频云雷达对冰云探测能力研究
投稿时间:2020-01-31  修订日期:2020-03-30  点此下载全文
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作者单位E-mail
吴举秀 山东省气象局大气探测技术保障中心 gurunmin@163.com 
杨蕾 青岛市气象局  
窦芳丽 国家气象卫星中心  
安大伟 国家气象卫星中心
 
 
基金项目:国防科工局民用航天预研项目(太赫兹测云成像技术研究);国家自然科学基金 (41305031);江苏高校优势学科建设工程资助项目(PAPD);
中文摘要:针对星载云雷达对冰云探测可行性分析的需求,分析了非球形冰晶对340 GHz电磁波的单散射特性,基于不同的体积散射模型,研究了非球形冰晶云的回波特性以及94\340 GHz云雷达双波长比DWR(dual wavelength reflectivity ratio),假定冰云垂直分布的情况下,探讨了星载94\340 GHZ云雷达DWR随高度的变化以及可以穿透的冰云厚度。(1)相比较94 GHz及220 GHz,冰晶粒子对340 GHz电磁波的散射能力增强,但是同时云对其的衰减也大大增加,340 GHz的衰减系数约是94 GHz的5-130倍;(2)340 GHz云雷达可以探测浅薄的含水量较小的冰云,基本可以探测云厚2 km、冰水含量IWC(ice water content)在 0.0001-0.2 g/m^3的冰云;含水量较多的厚云由于衰减,造成电磁波穿透能力大大降低,在假定的IWC垂直分布下,当最大IWC为1 g/m^3时,可探测厚约5 km内云厚的40%以上;(3)衰减也造成不同高度上相同滴谱的云有不同的DWR,IWC的大小及垂直分布影响了DWR的大小及电磁波探测云的厚度。衰减随着IWC增大而增大,高频云雷达电磁波衰减大,使得DWR变大,从而使DWR和谱的数浓度N0有关,因此利用DWR反演时,衰减订正非常重要。
中文关键词:星载94\340 GHz 云雷达  双波长比  衰减系数  测云厚度
 
Study on the Detection Capability to Ice Clouds for Space-borne Terahertz Dual-frequency Radar
Abstract:Aiming at the requirement of feasibility analysis for ice cloud detection by space borne cloud radar, the single scattering characteristics of non-spherical ice crystals to 340 GHz electromagnetic wave were analyzed, then the echo characteristics of non-spherical ice crystal cloud and dual wavelength ratio (DWR) of 94 \ 340 GHz cloud radars were studied based on different volume scattering models, while the variation of DWR with altitude and the thickness of ice clouds that can be penetrated were discussed assuming the vertical distribution of ice clouds. (1) Compared with 94 GHz and 220 GHz, the scattering ability of ice particles to 340 GHz electromagnetic wave is enhanced, but at the same time, the attenuation by clouds is also greatly increased, and the attenuation coefficient of ice clouds to 340 GHz wave is about 5-130 times that to 94 GHz wave. (2) The 340 GHz cloud radar can detect the shallow ice clouds with low ice water content (IWC), that is, ice cloud with thickness of 2km and IWC of 0.0001-0.2 g/m3 can be detected basically, and the electromagnetic wave penetration ability is greatly reduced due to the attenuation of thick clouds with more water content, when the maximum IWC reaches 1 g / m3 in the condition of the assumed vertical distribution of IWC, about more than 40% of cloud thickness for ice clouds within 5 km will be detected. (3) Attenuation also results in different DWR for clouds with the same drop spectrum at different heights. The value and vertical distribution of IWC affect the value of DWR and the thickness of the clouds detected by electromagnetic wave. The attenuation increases with the increase of IWC and the electromagnetic wave attenuation of high frequency cloud radars is larger, that make the DWR larger, so the DWR is related to the number concentration of the spectrum. As a result, the attenuation correction is very important when using DWR retrieval.
keywords:94\340 GHz  space-borne  cloud radars, Dual  wavelength reflectivity  ratio, Attenuation  coefficient,Detected  cloud thickness
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