氧气吸收率是利用氧气A吸收带进行被动测距技术计算的核心，将包含氧气A吸收带在内的无云天空背景辐射和黑体辐射作为研究对象，利用CART软件模拟计算了不同观测天顶角、不同时段、不同太阳天顶角的无云天空背景氧气吸收率分布，并与不同观测天顶角、不同距离下的黑体辐射氧气吸收率进行了比较分析，结果表明：当探测距离大于3 km时，黑体辐射的氧气吸收率大于无云天空背景辐射氧气吸收率，所以根据不同观测条件设置被动测距的氧气吸收率阈值，可提高对目标的探测概率，降低背景辐射对被动测距的影响。

Oxygen absorption rate is the core of passive ranging technology calculation which used oxygen A band. The cloudless sky background radiation and blackbody radiation which contained oxygen A absorption bands was researched. The oxygen absorption rate distribution of cloudless sky background was calculated under the different conditions of observation zenith angle, times and solar zenith angle used CART. Then the calculation results was compared with the oxygen absorption rate of blackbody radiation with different observation zenith angle at different distances. The results show that the oxygen absorption rate of blackbody radiation is greater than the oxygen absorption rate of cloudless sky background radiation when the detection distance is more than 3 km. So depending on different viewing conditions to set the oxygen absorption rate threshold will improve the detection probability of the target and reduce the influence of background radiation on passive ranging.