Differential Absorption Measurements of Atmospheric Methane Concentration

The differential absorption method with two He-Ne lasers is discussed for the monitoring of methane in the ambient atmosphere. Absorption coefficients of methane at He-Ne laser emiting wavelengths are measured in the laboratory. By using a pair of 3.3922μm laser lines, the measurements of methane concentration are made in outdoors. The average methane concentration of 1.77ppm in the natural atmosphere near the ground is obtained