Solar reflection band site automatic calibration by the Dunhuang site automatic observation radiometric calibration operational system

Solar reflection band of typical in-orbit payload was calibrated by the use of the Dunhuang site automatic observation radiometric calibration operational system (DARCOS) in 2018. Several automatic observation instruments were installed at Dunhuang site. DARCOS integrated product generation, acquisition, archiving, publishing, retrieval, downloading, user hierarchical management and performance monitoring functions together. Automatic calibration algorithm for AQUAODIS, JPSS1IIRS, FY2GISSR, FY3CIRR and FY4AGRI were developed. How to accurately measure the surface reflectance without human intervention and correct it to the payload viewing angle is an important subject needs to be solved. A surface reflectance algorithm based on surface radiance and total sky radiation was developed. The directionality calibration was performed using the micro-facet cosine linear kernel-driven (MICOKE) BRDF model. The reflectance was corrected by the site vicarious calibration campaign on August 7-9, 2018. The site correction factor exhibits two variations rules with increasing wavelength, which corresponds to the HIM detector design. The calibration results for 5 payloads between August 13 and December 31, 2018 were analyzed. Ratio of the apparent reflectance from space and ground base was used to judging the agreement. AQUAODIS (1.02-1.15), JPSS1IIRS (1.07-1.15), and FY3CIRR(1.10 to 1.19) are in good agreement with the automatic observation products of the site. FY2GISSR (1.25) and FY4AGRI (1.07-1.31) show differences changing by time. As an efficient independent calibration method, automatic calibration could be an effective supplement to the in-orbit calibration.