An evaluation of FY-3C satellite data quality at ECMWF and the Met Office

The present memorandum summarises the evaluation of microwave sounding data from the Chinese FY-3C polar orbiting satellite at the Met Office and ECMWF. Data from the MWTS-2 and the MWHS-2 instruments are evaluated and, where possible, the characteristics are compared to data from similar instruments with similar temperature or humidity sounding capabilities such as ATMS. MWHS-2 also features channels around the 118 GHz oxygen line, providing capabilities never before available from space. The joint evaluation in two systems is a novel aspect of NWP-based calibration/validation activities, allowing a better attribution of the findings. A very brief assessment of the other instruments relevant to NWP is also provided. The evaluation shows that MWTS-2 overall exhibits a promising noise performance, although crosstrack striping appears to be a stronger feature than for other instruments. The observations evaluated here are biased cold, to an extent that is unusual for similar instruments. The origin of these biases is not yet fully understood, but an improved antenna pattern correction may offer an explanation. An anomalous land/sea-contrast was found for some channels, and an empirical correction has been developed. The correction attributes this feature to cross-channel interference. The MWHS-2 instrument overall exhibits good data quality that is in line with that of other instruments for the 183 GHz channels. The main exception is a different spectral bias pattern for two of the 183 GHz channels, and this warrants further investigations. The new 118 GHz channels show expected data quality, with some air-mass dependent biases that may be linked to radiative transfer modelling or model biases. We provide recommendations for the continued evaluation of the FY-3C data for both instruments in the international cal/val team, in order to optimise the day-1 processing of the future FY-3D data.