Fig. 1. Optical path diagram of FTIR monitoring system

Fig. 2. Experimental measuring system

Fig. 3. Infrared spectral inversion process
(a): Characteristic absorption spectra of methane;(b): Measured spectrum;(c): Fit spectrum and original spectrum;(d): Residual spectrum

Fig. 4. Sewage discharge real-time map

Fig. 5. Methane measurement during an hour
(a): Concentration; (b): Emission rate

Fig. 6. Methane measurement in the day
(a): Concentration; (b): Emission rate

Fig. 7. Methane observed continually for 80 hours
(a): Concentration; (b): Emission rate

Fig. 8. Correlation of concentrations obtained by using FTIR and handheld instrument