Fig. 1. Background radiometer system structure

Fig. 2. Physical picture of background radiometer

Fig. 3. Operating principle of background radiometer

Fig. 4. Radiance receiving unit

Fig. 5. Schematic diagram of four quadrant detector imaging

Fig. 6. Signal collection process of spectrometer

Fig. 7. Schematic diagram of background radiometer calibration. (a) Calibrate the spectral radiometer; (b) transfer to the integrating sphere and calibrate the background radiometer

Fig. 8. Calibration curves of three spectrometers. (a) Visible near-infrared fiber spectrometer; (b) short wave infrared fiber spectrometer 1; (c) short wave infrared fiber spectrometer 2

Fig. 9. Inversion results of three spectrometers. (a) Visible near-infrared fiber spectrometer; (b) short wave infrared fiber spectrometer 1; (c) short wave infrared fiber spectrometer 2

Fig. 10. Full sky scanning results at different times on February 25th. (a) 11:00; (b) 11:30; (c) 12:20

Fig. 11. Fixed point observation data. (a) March 4th, sunny to cloudy; (b) March 6th, sunny; (c) March 8th, sunny