Fig. 1. Schematic diagram of dual-channel near-infrared LHR

Fig. 2. (a) Sun tracker; (b) Fiber optic switch; (c) Optical switch output signal

Fig. 3. (a) RF signal power spectrum; (b) Instrument functions

Fig. 4. (a) Heterodyne signal absorbed by CH₄; (b) Heterodyne signal absorbed by CO₂; (c) Relation curve between laser wavenumber and injection current for CH₄ measurement; (d) Relation curve between laser wavenumber and injection current for CO₂ measurement

Fig. 5. (a) Transmission of CH₄ in the atmosphere; (b) Transmission of CO₂ in the atmosphere