Fig. 1. Visible/infrared full sky imager. (a) Visible light imager; (b) infrared full sky imager

Fig. 2. YLU1 Ka-band millimeter-wave cloud radar

Fig. 3. Comparison of gray values with and without clouds at the same time

Fig. 4. Scatter diagram of cloud height and gray value before quality control in June, 2019

Fig. 5. Scatter diagram of low cloud height and gray value below 2500 m

Fig. 6. Scatter diagram and correlations of medium cloud height and gray value below 6000 m

Fig. 7. Scatter plots of medium and high cloud height and gray value above 6000 m

Fig. 8. Scatter diagram of cloud height and gray value after quality control in June, 2019

Fig. 9. Comparison of actual and inversion cloud heights in zenith direction

Fig. 10. The area within the zenith angle of about 30° near the zenith at 07:30 on June 4, 2019

Fig. 11. Three-dimensional distribution of gray value within 30°zenith angle of infrared cloud image at different cloud heights

Fig. 12. Relationship between downward infrared radiation and zenith angle cosine in clear sky

Fig. 13. Comparison between the cloud height obtained by linear inversion of the relationship between infrared radiation and zenith angle cosine and the cloud height obtained taking the zenith angle of about 30° near zenith