Fig. 1. Basic technical process for site calibration

Fig. 2. High-precision solar radiometer installed in Dunhuang test site. (a) In-situ observation; (b) measurement principle

Fig. 3. Comparison of aerosol optical depth (AOD) measurements between PSR and CE318. (a) Dunhuang; (b) Qinghai Lake

Fig. 4. Measurement process of self-calibration direct solar spectral irradiance radiometer (DIR)

Fig. 5. Measured direct solar spectral irradiance at Dunhuang test site

Fig. 6. Hyperspectral irradiance meter

Fig. 7. HIM measurement results. (a) Irradiance; (b) one day variation of irradiance at 550 nm

Fig. 8. Optical head design of automated test-site radiometer

Fig. 9. ATR long series measurement data of reflected radiance at Dunhuang radiation correction field

Fig. 10. Measurement principle of ATS

Fig. 11. ATS measurement results at Dunhuang test site

Fig. 12. Measurement principle of SCRS

Fig. 13. Measurement results of SCRS at Dunhuang test site^[58]

Fig. 14. Measurement principle of SER^[59]

Fig. 15. Automatic BRDF measurement system

Fig. 16. BRDF at 550 nm with different solar zenith angles at Dunhuang radiation correction field

Fig. 17. Portable BRDF measurement system

Fig. 18. Composition of unmanned aerial vehicle (UAV) BRDF measurement system

Fig. 19. Compact spectrometer loaded on UAV

Fig. 20. Water apparent optical property acquisition system (WAOPAS) (left image is measurement principle, and right image is functional composition)^[69]

Fig. 21. Functional modules of automated calibration software

Fig. 22. TOA reflectance output from automated calibration software (Terra MODIS band)

Fig. 23. Comparison of automated calibration and multi-site calibration results for FY-3C VIRR. (a) Channel 6; (b) channel 7

Fig. 24. On orbit changes of FY-3D MERSI-II calibration coefficient

Fig. 25. Average relative deviation of TOA reflectance of AVCS prediction and remote sensor observation

Fig. 26. Reflectance of Dunhuang test site^[80]

Fig. 27. Structure of global test site network radiometric calibration software^[80]

Fig. 28. Global calibration site network database structure^[80]

Fig. 29. Process of calibration task automatic planning^[83]

Fig. 30. Changes in reflectance calibration coefficients of FY-3B VIRR channels 1, 6, and 7 (2013—2016)^[80]

Fig. 31. Calibration slope time series of channels 1 and 2 of FY-3A MERSI^[84]

Fig. 32. Normalized response time series of FY-4A AGRI by multisite calibration tracking (from launch to June 2018)^[85]

Fig. 33. Wide dynamic range absolute radiometric calibration of channel 2 (550 nm) of FY-3A/C MERSI^[86]

Fig. 34. Integrated calibration and residual analysis of channel 1 of FY-3C MERSI (left image is distribution of fusion samples and integrated calibration results, and right image is distribution of calibration residual)^[87]

Fig. 35. Radiometric response consistency correction for FY-3A/B/C MERSI (left image is obtained before correction, and right image is obtained after correction)^[88]

Fig. 36. Normalized reflectance of each sensor of VIRR^[89]