A COMPARISON OF THE RETRIEVAL OF ATMOSPHERIC TEMPERATURE PROFILES USING OBSERVATIONS OF THE 60 GHZ AND 118.75 GHZ ABSORPTION LINES

Abstract:

The Microwave Temperature Sounder-II (MWTS-II) and Microwave Humidity and Temperature Sounder (MWHTS) onboard the Fengyun-3C (FY-3C) satellite can be used to detect atmospheric temperature profiles. The MWTS-II has 13 temperature sounding channels around the 60 GHz oxygen absorption band and the MWHTS has 8 temperature sounding channels around the 118.75 GHz oxygen absorption line. The data quality of the observed brightness temperatures can be evaluated using atmospheric temperature retrievals from the MWTS-II and MWHTS observations. Here, the bias characteristics and corrections of the observed brightness temperatures are described. The information contents of observations are calculated, and the retrieved atmospheric temperature profiles are compared using a neural network (NN) retrieval algorithm and a one-dimensional variational inversion (1D-var) retrieval algorithm. The retrieval results from the NN algorithm show that the accuracy of the MWTS-II retrieval is higher than that of the MWHTS retrieval, which is consistent with the results of the radiometric information analysis. The retrieval results from the 1D-var algorithm show that the accuracy of MWTS-II retrieval is similar to that of the MWHTS retrieval at the levels from 850–C1,000 hPa, is lower than that of the MWHTS retrieval at the levels from 650–C850 hPa and 125–C300 hPa, and is higher than that of MWHTS at the other levels. Comparison of the retrieved atmospheric temperature using these satellite observations provides a reference value for assessing the accuracy of atmospheric temperature detection at the 60 GHz oxygen band and 118.75 GHz oxygen line. In addition, based on the comparison of the retrieval results, an optimized combination method is proposed using a branch and bound algorithm for the NN retrieval algorithm, which combines the observations from both the MWTS-II and MWHTS instruments to retrieve the atmospheric temperature profiles. The results show that the optimal combination can further improve the accuracy of MWTS-II retrieval and enhance the detection accuracy of atmospheric temperatures near the surface.