临边大气红外背景辐射亮度的准确预测在我国新型飞行器的突防设计中具有十分重要的意义。MODTRAN是国际上通用的大气辐射传输计算软件，基于平衡态假设，计算可靠性好、精度高，在我国应用十分广泛。但MODTRAN预测曲线与飞行试验测量结果在50km以上差别显著，其原因是什么？如何才能准确预测50km以上的临边大气红外辐射亮度？本文主要针对这些问题开展研究。

首先建立了临边大气红外辐射平衡态和非平衡态的计算方法。对于平衡态，针对大气红外辐射重要组分，建立了红外辐射透过率、辐射亮度和太阳散射等的计算方法；对于非平衡态，建立了辐射强度、振动能级分布的迭代求解算法，结合辐射传输方程可计算大气临边非平衡辐射亮度。

第二，基于平衡和非平衡算法，研发一套具有自主产权的大气红外辐射计算程序（AIRTRAN），包含平衡态（AIRTRAN-LTE）和非平衡态（AIRTRAN-NLTE）两部分。AIRTRAN-LTE可用于计算分析不同昼夜、不同季节、多种组分的吸收系数，以及任意路径的辐射亮度；AIRTRAN-NLTE包括输入模块、辐射传输方程、统计平衡方程迭代模块，可用于计算非平衡态不同条件下的能级分布、辐射传输问题，得到临边大气非平衡辐射亮度。

第三，利用AIRTRAN-LTE分析了临边大气中波红外辐射，并与不同计算结果和实验数据进行了细致比较，验证了算法和程序的精度与可靠性；给出了不同大气模型下各组分气体在不同切向高度的贡献：①在地表附近，H₂O的含量变化对辐射贡献影响显著；对流层内，CO₂、H₂O、N₂、N₂O、CO的辐射贡献均达到10%以上；平流层内CO₂辐射贡献最大，超过70%，而O₃次之，其辐射贡献最大达到20%左右；低热层和中间层范围内CO₂对临边路径总辐射贡献最大，超过80%；②CO在高纬度地区所有高度的辐射贡献均超过10%；CH₄在所有高度范围内辐射贡献均不超过3%，在中波红外辐射计算中可忽略；③太阳散射辐射在不同太阳天顶角和方位角情况下对总辐射的贡献小，计算中可忽略。

第四，利用AIRTRAN-NLTE程序，开展50km以上大气临边非平衡辐射效应研究，计算CO₂振动能级在不同高度的分布，给出了昼夜、天顶角、碰撞反应对能级分布的影响：①对于4.3μm带，CO₂（v₃）白天在50km附近开始偏离平衡态，夜间在60km附近开始偏离平衡态；N₂（1）和CO₂ 626（00011）在80km以下具有相同的振动温度；CO₂（v₃）受太阳辐射影响很大；②对15μm带，CO₂（v₂）白天整体上在60-80km左右开始偏离平衡态，其中v₂振动量子数越高，偏离平衡态的大气高度越低、振动温度越高，并且次同位素的振动温度相比主同位素更高；③CO₂（v₂）夜间均在80km附近开始偏离平衡态CO₂（v₂）受太阳辐射影响很小。

最后，利用AIRTRAN-NLTE程序，结合辐射传输模型，给出15μm和4.3μm两个重要谱段的辐射亮度，并与我们的飞行试验数据进行了比较：50km以上时，AIRTRAN-NLTE计算结果与飞行试验数据相符，而MODTRAN在100km附近则相差2-3个量级。

综上所述，本文打通了临边大气红外辐射与非平衡效应理论预测从算法、程序到实际应用的全链条，对当前和未来我国新型飞行器突防设计具有非常重要的意义。

The accurate prediction of the limb atmospheric infrared background radiance is of great significance in the anti-defense design of new aircraft in our country. As an international general atmospheric radiation transfer calculation software, MODTRAN was developed based on the Local Thermodynamic Equilibrium (LTE) assumption. It has good calculation reliability and high precision, and has been widely used in our country. However, the prediction results of MODTRAN are significantly different from the experimental data above 50km. Why? How can we accurately predict the limb atmospheric infrared radiance above 50km? This paper mainly focussed on these issues.

Firstly, the calculation methods of the limb atmospheric infrared radiation for the LTE and non-LTE were established. For the LTE, the calculation methods of infrared transmittance, radiance, and solar scattering for the important components of atmospheric infrared radiation were established. For the non-LTE, the iterative solution methods of radiation intensity and vibrational energy level population were established. By combining these results with the radiation transfer equation, the non-LTE limb atmospheric radiance then could be caculated.

Secondly, based on the above LTE and non-LTE calculation methods, a set of Atmospheric Infrared Radiation TRANfer (AIRTRAN) calculation program with independent property rights was developed. AIRTRAN contains two parts: AIRTRAN-LTE and AIRTRAN-NLTE. AIRTRAN-LTE can be used to calculate and analyze the absorption coefficients of various components in day and night, different seasons, and the radiance of any path; AIRTRAN-NLTE consists of input module, radiative transfer equation, and statistical equilibrium equation iteration module. It can be used to deal with the non-LTE energy level population and radiative transfer problems under different conditions, and the non-LTE radiance of the limb atmosphere can be caculated.

Thirdly, according to AIRTRAN-LTE, the middle infrared radiation of the limb atmosphere was analyzed. By comparing with different computational results and experimental data in detail, the accuracy and reliability of the algorithm and program were verified. In addition, the contributions of atmospheric components at different tangent heights and different atmospheric models were obtained: (1) Near the surface, the change of H₂O content has a significant impact on the radiation contribution. In the troposphere, the radiation contributions of CO₂, H₂O, N₂, N₂O, and CO all reach more than 10%. In the stratosphere, CO₂ makes the biggest contribution to the radiation, of over 70%, followed by O₃, whose radiation contribution could reach up to about 20%.  In the lower thermosphere and mesosphere, CO₂ has the largest contribution to the total radiation along the limb path, exceeding 80%. (2) In high latitudes, the radiation contribution of CO at any altitude is more than 10% , while that of CH₄ is less than 3%. Thus, CH₄ can be ignored in the calculation of middle infrared radiation. (3) The solar scattered radiation has a small influence on the total radiation at different solar zenith and azimuth angles, and it can be ignored in the calculation.

Fourth, the AIRTRAN-NLTE program has been used to study the non-equilibrium effect of atmospheric limb radiation above 50 km, and calculate the distributions of CO₂ vibrational energy levels at different heights. The effects of day and night, solar zenith angle, and collision reactions on energy level population have been summarized: (1) For the 4.3 μm band, CO₂(v₃) begins to deviate from the equilibrium state near 50 km during the day, while near 60 km at night. N₂(1) and CO₂ 626(00011) have the same vibration temperature below 80 km. CO₂(v₃) is significantly affected by solar radiation. (2) For the 15 μm band, CO₂(v₂) begins to deviate from the equilibrium state at around 60-80km during the day. The higher the vibration quantum number of v₂ is, the lower the vibration temperature gets. The vibrational temperature of the secondary isotope is higher than that of the primary isotope. (3) CO₂(v₂) starts to deviate from the equilibrium state near 80km at night, and CO₂(v₂) is little affected by solar radiation.

Finally, by using the AIRTRAN-NLTE program and the radiative transfer model, the radiance of CO₂ 15 μm and 4.3 μm bands were caculated, and compared with our flight test data. When the altitude is higher than 50km, the AIRTRAN-NLTE calculation results are in good agreement with the flight test data, while MODTRAN differs by 2-3 orders of magnitude near 100km.

As a conclusion, the work of this paper has satisfactorily solved the problem that the equilibrium model cannot accurately predict the infrared background radiation of the limb atmosphere, and has opened up the whole chain of theoretical prediction of the limb atmospheric infrared radiation and the non-equilibrium effect from algorithm, program to practical application. It would be of great significance to the current and future anti-defense design of new aircraft in our country.