Research On THZ Radiation Characteristics And Instrument Parameter Design For Ice Clouds

In the atmosphere,a large range of ice clouds composed of ice crystal particles have a significant impact on the climate.On the one hand,ice clouds absorb thermal infrared radiation from the earth's surface and the atmosphere below them,causing climate warming.on the other hand,Ice clouds reflect incoming short-wave solar radiation into space,providing cooling.According to the scattering characteristics between the length of electromagnetic wave and the size of ice crystal,the closer the wavelength is to the size of ice crystal particles in the ice cloud,the more significant the scattering effect is.Many studies show that the size of ice crystal particles in the ice cloud is mainly concentrated in 20-600 um.Compared with the infrared and visible frequency band,the sounding instruments in the THz frequency band have unique advantages in observing the ice cloud.In U.S.and Europe,research on terahertz ice cloud sounding technology has been more than 20 years,a large number of airborne experiments and studies have been conducted for the characteristics of terahertz ice cloud scattering,and a single scattering database has been established,while in China the research is very little.The terahertz radiation characteristics of ice clouds is key for the ice cloud sounding technology.To understand how the parameters of the ice cloud affect the terahertz radiation transmission process,and to establish the correct particle scattering model is the key to calculate the terahertz radiation transmission process of the ice cloud.Based on the theory of atmospheric radiation transmission,Mie scattering theory in the atmospheric radiation transmission model is studied in this paper.In the DOTLRT radiation transmission model,the jacobian matrix of ice cloud parameters based on Mie scattering is calculated,and the terahertz ice cloud brightness temperature and the jacobian matrix of ice cloud parameters calculated by DOTLRT model are verified.Then,based on the DOTLRT model,the brightness temperature characteristics of ice cloud terahertz radiation were deeply studied,and the influences of ice cloud parameters(Dme,IWP,IWC,GWP,GWC),particle size distribution function and other factors on the brightness temperature of ice cloud terahertz radiation were quantitatively analyzed.Finally,the index demand of brightness radiometer instruments for ice cloud sounding is analyzed from the perspective of instrument parameters such as sounding frequency and observation geometry.Compared with the real observation of the brightness temperature and ARTS model,the study shows that DOTLRT radiation transmission model has a high accuracy in the calculation of atmospheric and ice cloud radiation transmission in the terahertz frequency band,which can meet the calculation requirements of the terahertz radiation brightness temperature of ice cloud,and can realize the rapid calculation of the jacobian matrix of ice cloud parameters.At terahertz frequencies,ice and graupel have obvious characteristics of resonance between particles and electromagnetic wave 183 GHz water vapor absorption spectrum parameters detecting ice cloud graupel particles and the ability of vertical profile,325 GHz,448 GHz water vapor absorption spectrum and 664 GHz,874 GHz window zone spectrum detecting ice particle parameters and the ability of vertical profile,scanning mode selection of conical scan more appropriate fixed observation angle,angle within 48 ? 58°have the best sensitivity.