Evaluation of the in-orbit performance of the microwave temperature sounder onboard the FY-3D satellite using different radiative transfer models

Abstract

The in-orbit performance of the Microwave Temperature Sounder (MWTS) onboard the Fengyun-3D (FY-3D) satellite is evaluated using the Community Radiative Transfer Model (CRTM) and the Radiative Transfer for the Television Infrared Observation Satellite Operational Vertical Sounder (RTTOV) model. Both radio-occultation data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Data Analysis and Archive Center and ERA-Interim analysis data from the European centre for Medium-Range Weather Forecasts are taken as inputs to the two fast radiative transfer models. The radio-occultation data are quality controlled and the collocation criterion between the radio-occultation data and the MWTS measurements is defined such that the spatial and temporal difference is <50 km and <3 h, respectively. The biases of MWTS channels 5–10 produced by both CRTM and RTTOV agree well over the oceans under clear sky conditions between 60° S and 60° N from July to December 2018. The mean biases simulated by the radio-occultation and ERA-Interim data are negative and the absolute values of the biases are <0.6 and <1.5 K for channels 5–10 of the MWTS, respectively. The biases at channels 4 and 11 between the CRTM and RTTOV simulations are inconsistent and require further investigation of the transmittance difference between the fast models. The standard deviation of the biases from the radio-occultation and ERA-Interim data are <0.5 and <1.8 K for the limited amount of collocated radio-occultation data. Asymmetrical patterns are detected for the MWTS through the scan angle-dependent bias. The long-term mean MWTS bias shows only a weak dependence on latitude, which suggests that biases do not vary systematically with brightness temperature.