Bias and Observation Error Characterization of the Fengyun-2F Stretched Visible and Infrared Spin Scan Radiometer for Its Radiance Assimilation

Bias correction and observation error quantification are two important components for satellite radiance assimilation. This paper examines both the bias and the observation errors of the Chinese Fengyun-2F Stretched Visible and Infrared Spin Scan Radiometer, as the first step towards its clear radiance assimilation. Totally 774,530 observations that passed a five-step quality control procedure during the period of July 1-9 in 2014 are collected to investigate the bias and observation errors both over ocean and land during daytime and nighttime, while the synthetic simulated clear radiance is calculated through the ECMWF ERA-Interim atmospheric and surface analysis and a fast radiative transfer model. It is found that a persistent warm bias exists for FY-2F S-VISSR channel 3, 4 and 5 during all times. In addition, both the bias and the observation errors of S-VISSR infrared channels vary with the surface types, generally with larger values over land than over ocean. The scan-position-dependent and the temporal-evolving bias of the S-VISSR infrared channels are also investigated in this study. Biases from the three surface channels exhibit complex dependence on the scan position and evolve with time, which implies both the scan position and temporal corrections are supposed to be incorporated into the S-VISSR bias correction scheme in the data assimilation system.