The recalibration of FY-3 MERSI reflective solar bands

Abstract

Medium Resolution Spectral Imager (MERSI) is a keystone instrument onboard Fengyun-3 (FY-3), the second generation of polar-orbiting meteorological satellites in China. There are three units currently in operation, in which FY- 3A and FY-3C were launched on May 27, 2008 and September 23, 2013, separately, in a sun-synchronous morning orbit with a local equator-crossing time of 10:30 AM in descending node, FY-3B 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 of 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 are relatively large at visible spectral bands. The overall degradation for 412 nm of FY-3A MERSI is about 42% until the end of 2013. To implement the on-orbit calibration updates, a multisite calibration tracking method has been developed to monitor the RSB radiometric response variation, and a daily calibration updating model is presented. FY-3A/B MERSI is recalibrated using the daily calibration model, and the data quality is monitored using Aqua MODIS. This paper presents the recalibration of FY-3A/B MERSI RSBs accounting for the temporal variation of radiometric response, demonstrates the improvement to the MERSI radiometric data quality and retrieved products, and discusses issues that need further investigation.