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The development of energy production and transportation industry is seriously threatened by the methane for its flammability and explosiveness. How to monitor the methane leaks in real time is an important and difficult problem. The gas filter correlation technology has strong selectivity and fast response, so it can accurately detect the presence and concentration of methane. According to whether an artificial lighting source is used, the gas filter correlation technology can be classified as active or passive types. Passive light source like the sun has the advantages of low cost, wide coverage and being harmless to operators. The detection precision can be improved by increasing the working band to gather more radiation energy on the basis of maximizing the ratio between the total absorption of the methane and the total optical transmission of the system. In this paper, the precision of using passive gas filter correlation technology to detect methane concentration is simulated and analyzed. The working band of the detection system is chosen to be 7μm - 8μm by considering factors such as atmospheric transmission and radiation interference, and it covers the characteristic absorption peak of methane at 7.658μm. The radiation intensity of saturated absorption reference channel and non-absorbing measurement channel detected by the system under normal temperature is analyzed and compared. Based on the Lambert Beer law, the numerical relationship between methane concentration and radiation intensity was determined by multi-point fitting of simulation data, and the linear correlation reaches 0.9998. The simulation results show that the theoretical minimum gas detection limit is 0.465PPM, and the relative error at 12PPM is 10%. With the increase of gas concentration, the error decreases rapidly, and it is 3% at 35PPM. Even if the water vapor with absorption interference in the working band is added, the relative error at 35PPM is only 4%, indicating that it is insensitive to interference. It shows great potential in gas quantitative detection in the future.
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