Estimating the Inversion Accuracy of Atmospheric Temperature and Water Vapor Profile Under Limb Sounding
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摘要: 针对在研仪器——大气辐射超高光谱探测仪的临边探测模式,模拟计算了大气温度和水汽的权重函数。以此为基础,利用信息量和权重函数线性化方法,结合仪器的可探测亮温阈值0.3 K,计算并分析6种大气状态下,大气温度和水汽混合比廓线在不同反演精度条件下可获得的光谱通道数,在满足最佳光谱通道数200的要求下,理论上预估其反演精度。温度廓线整体反演精度为0.6 K,水汽混合比廓线反演精度可达到5%,但热带大气在16~20 km高度的水汽廓线反演精度仅为10%。反演精度预估,仅提供了一种全面认识仪器性能的方法,精度的确定还有赖于真实探测数据的获取和反演方法。Abstract: Profiles of atmospheric temperature and water vapor are important for studying atmospheric state and play an important role in the energy balance of earth-atmosphere system. Limb remote sensing is an important means to obtain the profile of atmospheric parameters. The atmospheric radiation ultra-high spectral detector developed by Shanghai Institute of Technical Physics, Chinese Academy of Sciences, has a detection band range of 650-3050 cm-1 and the spectral resolution on limb view is as high as 0.015 cm-1, which will be the highest spectral resolution that the world's Fourier spectral detector can achieve. A method by using information and weighting function linearization are proposed to evaluate the inversion accuracy of the research instrument in advance. Weighting functions of atmospheric temperature and water vapor at 16 different tangent points are simulated and calculated by RFM model. The degree of signal freedom and the entropy reduction are also calculated by the information content method, and the optimal number of inversion channels is determined to be 200 by the stepwise iterative algorithm. Combined with the threshold (0.3 K) of detectable brightness temperature and the linearized weighting function of the instrument, the available spectral channel numbers of atmospheric temperature and volume mixing ratio of water vapor profiles under different inversion accuracy of six atmosphere models (US standard atmosphere, tropical atmosphere, middle-latitude summer atmosphere, middle-latitude winter atmosphere, subarctic summer atmosphere, subarctic winter atmosphere) are calculated and analyzed, and the inversion accuracy is estimated theoretically. On the demanded optimal 200 channels, the inversion accuracy of the whole temperature profile is 0.6 K, but if the inversion accuracy of the temperature profile is required to be 0.5 K, the number of channels available for inversion at a higher tangent height is smaller. Except the tropical atmosphere model, there are enough channels for the other five atmosphere models meeting 5% accuracy demands of the inversion of water vapor volume mixing ratio profiles. However, the inversion of the water vapor profile of the tropical atmosphere has barely enough channels at 16-20 km for 10% relative inversion accuracy of volume mixing ratio. The number of channels usable for atmospheric parameters retrieving increases by the decreasing of inversion accuracy. Among six atmosphere models, the tropical atmosphere is relatively special and its inversion accuracy is lower, which may be related to the unique temperature profile of the tropical atmosphere. There is no isothermal layer in the tropical atmosphere, which may lead to fewer atmospheric parameter inversion channels near the height of sharp temperature transition.
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Key words:
- limb sounding;
- weight function;
- information content;
- inversion accuracy
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表 1 对应不同光谱通道数的大气温度和水汽在11.5 km和25.3 km切点高度信号自由度和熵减少量总和
Table 1 The sum of degree of signal freedom and entropy reduction at tangent heights of 11.0 km and 25.3 km for atmospheric temperature and water vapor for different channel numbers
光谱通道数 温度(11.5 km) 水汽(11.5 km) 温度(25.3 km) 水汽(25.3 km) 信号自由度 熵减少量 信号自由度 熵减少量 信号自由度 熵减少量 信号自由度 熵减少量 5 2.194 11.07 2.179 4.89 2.260 10.74 2.116 4.23 10 2.789 11.53 2.765 5.34 2.887 11.23 2.719 4.69 20 3.405 11.98 3.340 5.77 3.510 11.69 3.353 5.16 50 4.221 12.58 4.077 6.31 4.330 12.29 4.217 5.80 100 4.840 13.03 4.635 6.71 4.949 12.74 4.877 6.28 200 5.460 13.48 5.227 7.14 5.549 13.18 5.533 6.75 300 5.825 13.74 5.581 7.40 5.882 13.42 5.921 7.03 400 6.085 13.93 5.837 7.58 6.111 13.58 6.179 7.22 500 6.288 14.08 6.038 7.73 6.288 13.71 6.383 7.37 表 2 6种大气不同温度反演精度条件下可获得的光谱通道数
Table 2 Available channel numbers under six different atmospheric temperature inversion accuracy conditions
大气种类 精度/K 切点高度 0.0 km 4.6 km 11.5 km 16.1 km 20.7 km 25.3 km 34.5 km 0.4 0 855 341 39 8 8 0 美国标准大气 0.5 3822 20346 8079 404 242 199 40 0.6 8340 38723 22157 3353 1451 988 244 0.4 0 328 6542 0 0 0 1 热带大气 0.5 150 17435 36485 9 19 88 72 0.6 1463 36617 67314 142 369 474 582 0.4 0 437 5052 8 2 0 0 中纬度夏季大气 0.5 601 17623 20875 254 173 115 57 0.6 2717 36653 50575 2417 1189 571 397 0.4 0 2308 134 98 43 16 0 中纬度冬季大气 0.5 2005 24629 1448 789 502 235 33 0.6 9562 43214 16853 7924 5075 1349 201 0.4 0 769 69 39 10 0 0 副北极夏季大气 0.5 1936 21870 1503 481 261 126 41 0.6 5587 39388 11463 4279 2036 731 276 0.4 0 4155 106 116 79 25 0 副北极冬季大气 0.5 43 28853 1257 1019 822 250 65 0.6 8458 47559 13159 9734 7042 1407 262 表 3 6种大气不同水汽混合比相对反演精度条件下可获得的光谱通道数
Table 3 Available channel numbers under six different volume mixing ratio of water vapor inversion accuracy conditions
大气种类 精度/% 切点高度 0.0 km 4.6 km 11.5 km 16.1 km 20.7 km 25.3 km 34.5 km 美国标准大气 5 321 19751 8897 1548 1155 2682 1403 10 1785 30326 17579 14124 12749 12148 8797 热带大气 5 0 18484 13144 0 0 785 1791 10 0 27393 21039 4108 6957 9057 9279 中纬度夏季大气 5 0 19728 12208 535 691 2081 2204 10 25 28958 19973 11114 11433 11615 10160 中纬度冬季大气 5 494 17679 5445 2451 2579 2686 887 10 2900 29436 15702 16700 14937 12417 7803 副北极夏季大气 5 42 20212 6505 2042 2759 3285 2235 10 550 29661 15914 15428 15595 13479 10273 副北极冬季大气 5 3873 14174 5223 2519 3092 2206 918 10 13723 26523 15956 17351 15782 12326 8048 -
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