目标红外被动测距的实现同气体及其波段的选取密切相关。氧气A吸收带具有独特的谱线结构, 对于火箭羽流或者高温辐射体的距离探测, 氧气A吸收带是最佳的距离反演通道。利用该特点, 详细研究了逐线积分算法(LBLRTM), 并设计了氧气A带吸收系数及标准光谱计算软件；利用A吸收带吸收光谱带外数据, 采用多项式拟合方法, 实现基线(baseline)拟合, 进而得到带平均透过率；在不同的距离条件下, 将两种带平均透过率进行对比, 误差在1.9%左右, 拟合精度较高, 该方法为后续距离的精确反演提供了理论依据。

Realization of passive ranging based on infrared radiation has high correlation with band selection of gas. Oxygen ‘A’ absorption band has an unique spectral structure. The band is the best inversion channel of distance, such as detecting rocket plume and high temperature radiation. LBLRTM is researched in detail and the software of oxygen‘A’band absorption coefficient and spectrum calculation is designed using its specialty. Making use of the out-of-band data, band average transmittance is obtained by polynomial fitting baseline. Finally, under the different distance conditions, through the comparison of the two transmittance, the error is about 1.9%. So, this method provides the subsequent distance inversion with theoretical foundation.