Fig. 1. Principle of laser heterodyne detection

Fig. 2. HITRAN database and FTIR spectral data

Fig. 3. Schematic diagram of laser heterodyne radiometer

Fig. 4. Sun tracker

Fig. 5. RF circuit

Fig. 6. Signal spectrum and function of the system

Fig. 7. Measured heterodyne signal and reference data

Fig. 8. Comparison between measured and simulated atmospheric transmittance spectra of HDO

Fig. 9. Forward data and Inversion results