Research On Radiation Characteristics And Inversion Algorithms Of Trace Gas Terahertz Limb Soundings

Trace gases are important components of the atmosphere,and they play an important role in the evolution of Earth's life,global climate change,and the development of atmospheric chemistry.In recent years,environmental problems such as ozone holes and photochemical smog caused by changes in trace gas content have become more and more serious.Therefore,it has become extremely urgent to achieve high-precision detection of global trace gases.The satellite limb sounding mode can avoid surface radiation and has a long observation path.It has high vertical resolution and high spatial coverage,and is suitable for the detection of trace gases in the middle and upper atmosphere of 10-100 km.The terahertz band not only has high sensitivity in the visible light band,but also has the ability to penetrate in the microwave band.It has its unique advantages in the detection of atmospheric components in the upper and middle layers.Trace gas molecules have rich characteristic absorption lines in the terahertz band,so the terahertz limb sounding has the ability to measure the vertical distribution of atmospheric trace gas densities with high accuracy,and has become the main method of trace gas detection in the world.At present,the spaceborne terahertz limb sounders have been launched internationally,and has successfully realized the remote sensing detection of various trace gases.However,China is still blank in the field of satellite limb sounding,lacking the research on key technologies such as radiation characteristic analysis and inversion algorithm development.Aiming at the above problems,this article based on ARTS radiative transmission mode and load detection model to calculate the terahertz limb sounding brightness temperature,and then based on the simulated brightness temperature and the actual observed brightness temperature data,a trace gas neural network and an optimal estimation inversion algorithm were implemented.Through the full-link simulation test of the trace gas terahertz limb sounding,the key issues such as the trace gas radiation characteristics,detector frequency channel selection,inversion algorithm optimization,and detection accuracy analysis in terahertz limb sounding are studied.In this paper,the radiation characteristics of terahertz edge detection are studied,and the knee height,concentration sensitivity and background temperature profile sensitivity of different trace gas terahertz limb sounding are obtained.On this basis,two inversion algorithms for trace gas limb sounding,neural network and optimal estimation,are realized,which can meet the requirements of trace gas limb sounding accuracy,and simulation experiments show that the former inversion accuracy is higher.The above research results can can provide key technical support for the future development of trace gas terahertz limb sounder in China.