Recalibration Model of MWHTS’historical data onboard FY-3C Satellite

The microwave radiation data of the earth’s surface and atmosphere observed by the spaceborne microwave radiometer are a basic source for numerical weather prediction and climate research. Certain bias exists between the data of different or the same radiometers over a long period of time due to the difference in the response characteristics and calibration absolute reference between each sounder and variation of the on-orbit working conditions. If these biases are not corrected, then they will have significant implications for long time series applications (such as climate studies) and may even lead to erroneous results. In addition, absolute calibration of onboard data cannot be performed because the absolute reference for calibration is unobtainable at present. Therefore, other relative calibration methods should be used to evaluate the stability and variation characteristics of the radiometer. In this paper, a correction model for the calibration biases of the microwave humidity sounder is established, considering the principle of system responses and on-orbit calibration, which is also called re-calibration methods, based on OMB technique (observed brightness temperature (O) minus simulated brightness temperature (B)). Using the re-calibration methods, L1 level observation data of the FY-3C microwave humidity sounder were analyzed and the re-calibration coefficients were calculated. Then, the re-calibration coefficients were verified using two data sets. The residual and validation results show that the time series of the recalibration findings is stable, and some abnormal fluctuations in the original OMB biases have been well corrected after re-calibration, indicating that the re-calibration methods are valid. The method is based on the system responses of microwave humidity sounder. Therefore, it is also applicable to other FY-3 series satellite microwave humidity sounders for calibration bias correction. When using the same Radiative Transfer (RT) model, this re-calibration methods can achieve consistent calibration of FY-3 series satellite microwave humidity sounder data. © 2023 Science Press. All rights reserved.