为了实现测温红外热像仪的外场精确测温，研究了大气透过率的二次标定。建立了红外热像仪的外场远距离测温标定模型，采用一个标准面源黑体和红外热像仪对大气透过率进行了二次标定。首先，用标准面源黑体的设置温度标定大气透过率的二次修正系数；然后，在已知目标感兴趣区域发射率的情况下，用二次修正系数对未知辐射源测量值进行修正，实现未知辐射源目标辐射温度的准确测量。实验显示，随黑体设置温度从50 ℃不断升高(二次大气透过率近似为1)，大气二次透过率修正系数在50~100 ℃内迅速下降，在100~200 ℃内下降趋势减缓，逐渐接近于约为0.7的常数。实验结果为测温红外热像仪外场精确测温提供了保证。

To achieve the accurate temperature measurement in fields by infrared thermal imagers, the second calibration of atmospheric transmission was researched. A calibrating model for temperature measurement by infrared thermal imagers in a far distance was established, and an infrared thermal imager and a standard expanded area blackbody were used to do the second calibration of atmospheric transmission. Firstly, the setting temperature of the standard blackbody was used to calibrate the secondary calibration coefficient of atmospheric transmission. Then, assuming the emissivity of interested area of a object to be known, the secondary calibration coefficient was used to calibrate the measuring values of a unknown radiation object and to implement the accurate measurement of radiation temperature of the radiation object. Experiments show that as the setting temperature for the blackbody increases from 50 ℃ (the second atmospheric transmission is approximately equal to 1), the second calibration coefficient of the atmospheric transmission decreases rapidly in the temperature of 50~100 ℃, and decreases more and more slowly in the range of 100~200 ℃. Gradually, it is close to a constant value 0.7. These results can provide references for the accurate temperature measurement by infrared thermal imagers in fields.