Study On Global Precipitation Retrieval And Typhoon Simulation Based On The Microwave Humidity And Temperature Sounder(MWHTS)onboard FY-3C Satellite

Precipitation is an important parameter of climate characteristics and plays an irreplaceable role in the global water cycle,regional climate change,and numerical weather prediction.On-board microwave remote sensing is an important way to obtain precipitation information.Microwave Humidity and Temperature Sounder(MWHTS),which is onboard the polar-orbiting meteorological satellite Fengyun 3-C(FY-3C),is an important sensor to detect global atmospheric humidity and temperature distribution,precipitation,typhoons and other extreme weather.Based on the in-orbit observation remote sensing data of FY-3C/MWHTS,a global precipitation retrieval algorithm and a typhoon simulation experiment are established.Among them,the global precipitation retrieval algorithm is utilized to retrieve the global precipitation rate(mm/hr),providing high-precision precipitation for applied research in the field of atmospheric science.The typhoon simulation experiment can be used to simulate the brightness temperature of the FY-3C/MWHTS,and to make up for the shortcomings of the polar-orbiting satellites that cannot be quickly and continuously observe the typhoon.This paper first analyzes the principle of atmospheric microwave radiation transmission,and introduces the fast radiation transfer model CRTM(Community Radiative Transfer Model,CRTM)and RTTOV(Radiative Transfer Model for TOVS,RTTOV).These basic research work provides a theoretical basis for the subsequent global precipitation retrieval and typhoon simulation based on FY-3C/MWHTS.In this paper,by analyzing the simulated brightness temperature of 15 channels from FY-3C/MWHTS under different weather conditions(clear sky,water cloud,rain cloud),a global precipitation detection algorithm for FY-3C/MWHTS in-orbit remote sensing data is proposed.The algorithm includes a global ocean precipitation detection algorithm and a global land precipitation detection algorithm.The results show that the accuracy of ocean and land precipitation detection results are 99% and 96%,respectively,and the accuracy of precipitation detection results is high.The global precipitation detection algorithm can effectively determine precipitation events and has high application value.In the global precipitation retrieval study based on FY-3C/MWHTS,the L1 level brightness temperature of MWHTS and the Multi-Satellite Precipitation Analysis(TMPA)3B42 product data from the Tropical Rainfall Measuring Mission(TRMM)are used.Global precipitation retrieval uses multiple linear regression and BP neural network retrieval algorithms to retrieve the precipitation rate.The 183.31 GHz channels near the water vapor absorption line are used to determine the convection type,and a comparison of 10 models(20 species of ocean,20 species of land;40 species in total)of precipitation retrieval are carried out using two different retrieval algorithms.The results show that the convective type has positive effects on the global ocean and land precipitation retrieval,and both improve the accuracy of precipitation retrieval.It is indicated that the classification of convective types used in this study is reasonable and scientific in the precipitation retrieval.In addition,the precipitation rate retrieval in the typhoon area based on FY-3C/MWHTS is performed,and the typhoon precipitation retrieval is realized.In order to improve the accuracy of precipitation retrieval,combined with the research of precipitation detection and precipitation retrieval,an improved algorithm based on FY-3C/MWHTS for global precipitation retrieval is proposed.Precipitation detection algorithm is added to the improved algorithm,and the optimal precipitation retrieval algorithm is selected for different convection types according to the 40 precipitation models proposed above.The correlations between ocean and land precipitation retrieval results are 0.82 and 0.74,respectively.The improved precipitation retrieval algorithm has higher precision than before,which shows that the global ocean and land precipitation retrieval algorithm proposed in this study has high application value.In order to address the problem that FY-3C cannot continuously observe the rapid change of typhoon and strengthen the monitoring of typhoon,this study proposes a method based on FY-3C/MWHTS to simulate the typhoon brightness temperature in the western Pacific.First,the brightness temperature of FY-3C/MWHTS is simulated using the WRF and RTTOV model.Then,the simulated brightness temperature is linearly corrected according to different FOV(field of view;FOV),channel and latitude bands.Finally,as an application of simulation results,precipitation detection algorithm is utilized to detect precipitation in the typhoon area.Accurate precipitation detection rate not only illustrates the effectiveness of the precipitation detection algorithm,but also reflects the accuracy of the typhoon simulation and simulated brightness temperature correction methods used to some extent.