On-orbit calibration analysis of FY-4A AGRI solar bands

Abstract

FengYun-4A (FY-4A) is the first three-axis stabilized geostationary meteorological satellite in China, which was launched in the early morning of 11 Dec., 2016. Advanced Geosynchronous Radiation Imager (AGRI) is one of the four payloads onboard FY-4A, and acquired the first image on 20 Feb., 2017. FY-4A AGRI contains 14 spectral bands, in which 6 bands are in reflective solar region, with the nominal wavelengths at 0.47, 0.65, 0.825, 1.375, 1.61 and 2.25μm. The spatial resolution is 0.5 km for 0.65 μm band, 2 km for the shortwave infrared bands and 1 km for others. AGRI is designed with a solar diffuser, however it revealed the insufficient capacity for in-flight calibration mainly due to the partial aperture effect. The first vicarious calibration field campaign was conducted at the Dunhuang site of China Radiometric Calibration Site (CRCS) in Apr. 2017. It revealed the large bias of the AGRI data calibrated using the prelaunch calibration parameters, mostly underestimated. Using multiple land sites in Asia and Oceania, the calibration correction factors were derived combined with the CRCS data. The sensor's on-orbit radiometric response variation and observation bias against the simulated radiation were also monitored. It revealed that the bands at 0.65 μm was most stable, while 0.47 μm band showed the large degradation with an annual rate nearly 17%. In this paper, the calibration status of the FY-4A AGRI solar bands was presented.