The radiometric performance of FY-3A/B MERSI reflective solar bands

Medium Resolution Spectral Imager (MERSI) is a keystone instrument onboard Fengyun-3 (FY-3), the second generation of polar-orbiting meteorological satellites in China. The first unit still in operation is FY-3A which was launched on May 27, 2008 in a sun-synchronous morning orbit with a local equator-crossing time of 10:30 AM in descending node. The second unit still in operation is FY-3B which was launched on November 5, 2010, in an afternoon orbit with an equator-crossing time of 1:30 PM in ascending node. FY-3 MERSI provides global coverage on top-of-atmosphere (TOA) radiances used for a broad range of scientific studies of the Earth’s system. Nineteen of the 20 MERSI spectral bands are reflective solar bands (RSBs) from 412 NM to 2130 nm, which cannot be absolutely calibrated onboard. The long-term on-orbit response changes of FY-3A/B MERSI are relatively large at visible bands. A multisite calibration tracking method has been developed to monitor the RSB radiometric response variation, revealing that the overall degradation for 412 nm of FY-3A MERSI is about 43% until June 2014. A daily calibration updating model is developed to recalibrate FY-3A/B MERSI, and the data quality is monitored using SNO targets against Aqua MODIS. This paper demonstrates the radiometric performance of FY-3A/B MERSI RSBs after recalibration accounting for the temporal variation of radiometric response. The recalibrated MERSI shows good agreement with MODIS. For FY-3B MERSI band 1 (470nm), the overall percentage difference (Mean±Std) is within 4%.