Methane concentration measurement method in rain and fog coexisting weather based on TDLAS

A method of methane concentration measurement in rain and fog coexisting weather based on the tunable diode laser absorption spectroscopy combined with the Monte Carlo scattering model is proposed. The Monte Carlo scattering model is utilized to calculate the attenuation signal caused by the scattering of rain and fog. The comparative experiments were conducted in weather with and without rain and fog coexistence to verify the feasibility of using this method to eliminate the disturbance caused by rain and fog scattering. The results show that the corrected concentration obtained by this method is more similar to the reference concentration. Taking the 5000 ppm reference concentration as an example, the relative bias obtained from the uncorrected concentration and the corrected concentration is 21.64 % and −0.6 % respectively. Meanwhile, the results demonstrate the minimum detection limit of this system is 1.97 ppm and the system has great linearity and stability in rain and fog.