太赫兹波长和典型卷云冰晶粒子尺度处于同一量级,是理论上遥感卷云微物理参数(粒子尺度和冰水路径)的最佳波段.结合183,325,462,664,874 GHz通道的辐射传输特性,通过通道亮温差、亮温差斜率等五个参数量化粒子尺度和冰水路径对太赫兹辐射光谱的影响,基于加权最小二乘法建立了多重查找表反演卷云微物理参数的方法,并通过模拟数据序列进行了理论反演误差分析.结果表明:多重查找表反演方法可实现粒子尺度50—500μm和冰水路径10—500 g/m2范围内卷云微物理参数稳定、有效的反演.与只采用亮温差特征或亮温差斜率特征相比,粒子尺度的反演误差分别降低了68.78%和60.28%,冰水路径的反演误差则分别降低了78.17%和49.01%.对反演结果进行不确定度分析表明,粒子尺度和冰水路径的不确定度与粒子尺度和冰水路径的大小相关,冰水路径的不确定度分布在0—15 g/m2范围内,粒子尺度的不确定度分布在0—20μm范围内.研究结果对于进一步发展太赫兹波被动遥感卷云技术、提高卷云参数的反演精度具有重要借鉴意义.%Cirrus is an important regulator for the flow of radiant energy in the earth-atmosphere system through the processes of scattering and absorption of radiation. In order to satisfy the urgent requirement for accurate retrieval of cirrus microphysical properties, terahertz wave is expected to be the best waveband for inverting cirrus particle size and ice water path, with terahertz wavelengths on the order of the size of typical cirrus particles. There is an urgent need for establishing stable and accurate inversion method. A new retrieval method for particle size and ice water path is developed based on multiple lookup tables for spaceborne measurements of brightness temperature spectrum of 183 GHz, 325 GHz, 462 GHz, 664 GHz, and 874 GHz channels. Five parameters are derived to quantify the effects of particle size and ice water path on terahertz radiation spectrum due to the scattering of ice clouds, manifested by brightness temperature difference, brightness temperature difference slope, etc. To retrieve cirrus microphysical parameters, a weighted least square fit that matches the modeled parameters is used. The analysis of retrieval errors are conducted by a simulated data series and the results are compared with those retrieved by the other two methods, i. e., difference method and slope method. The results retrieved by the multiple lookup table method are much closer to the simulated data series than those from the other two methods. It is indicated that the method introduced here is a stable and valid method of inverting particles between 50 and 500 μm and ice water path between 10 and 500 g/m2. Compared with the errors from the difference-featured method and slope-featured method, the retrieval errors are reduced by 68.78%and 60.28%for particle size, 78.17%and 49.01%for ice water path. The analyses of retrieval uncertainties show that, in general, uncertainties of particle size and ice water path vary with particle size and ice water path. The ice water path uncertainties mainly spread in a range of 0–15 g/m2. The particle size uncertainties fluctuate within a range of 0–20 μm. In other words, for small particle size range, the uncertainties are 0–5 μm for thick clouds and 5–20 μm for thin clouds. However, for large particle size range, the uncertainties are 0–5 μm for particles larger than 300 μm and 5–15 μm for those smaller than 300 μm. The results will be helpful for further developing the terahertz wave remote sensing of cirrus microphysical parameter technology. Moreover, it is also an important reference to the improvement of cirrus retrieval accuracy.
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