Fig. 1. Peak absorption simulation near 6 046.1~6 047.6 cm^-1（P=1 atm，T=296 K，L=1 m，χCH4=0.000 2%，χCO2=0.04%，χH2O=0.2%，χCO=0.000 2%，χH2S=0.000 2%，χSO2=0.000 2%）

Fig. 2. Schematic diagram of absorption component generation(ΔνV=1 cm-1,ωm=0.35 cm-1）

Fig. 3. Simulation result（P=100 mbar，T=296 K，ΔνV=0.04 cm-1，ωm=0~900 MHz）

Fig. 4. Schematic diagram of FMS current modulation system

Fig. 5. Fitting of absorption component signal peaks

Fig. 6. Fitting local example images

Fig. 7. Actual measured slope of absorption component signal （1 653.72 nm， 20 000 ppm）

Fig. 8. Analysis results of FMS signal amplitude linearity

Fig. 9. FMS absorption component signal peak to peak results

Fig. 10. Allan variance