Evaluation of long-term performance of microwave radiometers onboard Chinese Fengyun satellites

Abstract: Accurate brightness temperature (BT) is a top priority for retrievals of atmospheric and surface properties. Microwave Radiation Imagers (MWRI) on Chinese Fengyun-3 (FY-3) serial polar-orbiting satellites have been providing abundant BT data since 2008, showing great potential for retrievals of atmospheric parameters and surface properties. Much work has been done to evaluate short-term MWRI observations, but it remains unclear on the long-term performance of MWRI. In this paper, the operational MWRI BT during 2012-2019 was carefully examined by using the simultaneous Advanced Microwave Scanning Radiometer 2 (AMSR2) BTs as the reference. A significant correlation between BTs from MWRI and AMSR2 was found. The BT difference between MWRI/FY3B and AMSR2 during 2012-2019 increased gradually over time. As compared with MWRI/FY3B, MWRI/FY3D BTs over land were much closer to those of AMSR2. The ascending and descending orbit difference for MWRI/FY3D is also much smaller than that for MWRI/FY3B. Both suggest the improvement of MWRI/FY3D over MWRI/FY3B. A substantial BT difference between AMSR2 and MWRI was found over water, even exceeding 5 K at the vertical polarization channels. A similar BT difference was found over polar water based on the simultaneous conical overpassing (SCO) method. Radiative transfer model simulations suggested the substantial BT differences at the vertical polarization channels of MWRI and AMSR2 over water were partly accounted for by their difference in the incident angle; however, the underestimation of the operational MWRI BT over the water was still a very important issue.

Keywords:
• MWRI,
• AMSR2,
• brightness temperature,
• FY-3 satellites,
• Calibration