VALIDATION OF FY-3 MWTS CHANNEL 4 MEASUREMENTS USING COSMIC RADIO OCCULTATION DATA

Abstract

With high accuracy and stability of GPS radio occultation (RO) data in the stratosphere, COSMIC data is used to validate the Microwave Temperature Sounder (MWTS) channel 4 (ch4) measurements on serial FY-3 satellite platforms. A 2-year comparison between the simulated and observed T_b for MWTS ch4 shows that both MWTS observed T_b on FY-3A/3B in lower stratosphere are overestimated, especially in the tropics and summer of high-latitude region. The trends of T_b bias are more consistent on both FY-3A/3B satellites in the two years. The variations of T_b bias for MWTS ch4 in four latitude-zones are quite different: the T_b bias is obviously positive about 2∼4 K in the tropics, and is stably positive about 1 K in the mid-latitude, while the T_b bias is evidently varied with seasons from negative in winter to positive in summer in high-latitude, particular in southern high-latitude the difference of T_b bias among seasons is about 5 K, such strong dependence on environment temperature for T_b bias is not mainly caused by the shifted central frequency. In the tropics the difference of the observed and simulated T_b is more significant, and the influence of matching samples in the tropics on the global T_b bias is more than 20%, which implies that it should be cautious to use the validating results derived from COSMIC in the tropics.