A Modified Limb Correction Algorithm for the Microwave Temperature Sounder of FY Polar-Orbiting Satellites

As a new generation of microwave temperature sensor independently developed by China, the microwave temperature sounder-III (MWTS-III) onboard the polar-orbiting satellite FY-3E has 17 channels that provide temperature information from multiple atmospheric layers, making it an indispensable instrument for meteorological research. However, due to the limb effect caused by its cross-track scanning mode, it is impossible to directly observe weather changes using the MWTS-III brightness temperature data. Currently, the limb correction algorithm is an important method to eliminate the limb effect. However, it is difficult to apply existing limb correction methods with fixed parameters due to the newly added channels of MWTS-III. The results of our study show that while the old algorithm can effectively correct the limb effect in most channels of MWTS-III, there are still some limb effects in the corrected results of channels 5-7. On the other hand, the new algorithm can significantly improve the shortcomings of the old method and more accurately eliminate limb effects. In addition, by comparing the limb correction results under different training data, we found that the correction results of the new algorithm have a certain dependence on the training data, and using the same month in the previous year can achieve better correction results. Finally, it has been proved to be applicable to all channels of MWTS-II onboard FY-3D. Specially, the new algorithm can improve the shortcomings of the old algorithm in correcting the limb effect for MWTS-II channel 7, including the lower average brightness temperature at the orbit edge, discontinuous spatial distribution of brightness temperature, and the existence of abnormally low values.