Research On The THz Wave Atmospheric Propagation Modeling And Remote Sensing

Research on propagation characters of Terahertz(THz)wave through tropospheric aerosol and clear-air atmospheric has important academic significance and broad application prospects in the fields of line-of-sight and Earth-space communication,remote sensing and radar detection.Based on multiple scattering theory,the terahertz wave propagation characteristics through rainfall,fog and urban aerosols are studied.340 GHz terahertz atmospheric transmission test system is calibrated and atmospheric attenuation data are measured.The equivalent height models that is used to estimate the zenith attenuation are modified.The atmospheric brightness temperatures of the clear sky and the ice crystal cirrus are calculated by the ARTS model.The altitude variation of the brightness temperature contribution along the Earth-space path at water vapor and temperature detection channels are analyzed.The brightness temperature and atmospheric attenuation with the background of clear-air and cirrus are studied and the cirrus detection channels are suggested.The main contributions and results are as follows:1.The absorption mechanism of THz wave by atmospheric molecules is introduced based on the molecule structure.The atmospheric attenuation of wave up to 10 THz is calculated and different window or peak frequencies are suggested for different applications.The scattering characters of THz wave through aerosols are analyzed based on the multiple scattering theory,especially for window frequencies.The scattering character of raindrop is calculated using Mie theory,and single and multiple scattering characters are studied for rain of different regions and different rain drop size distribution models.The applicable frequency range of Rayleigh approximation on fog attenuation is determined via the comparison with results of single scattering.The transmittance of THz wave through urban aerosols are discussed by comparing to the results of infrared waves.Better transmittance performed by THz wave is inferred in quantity.2.A large part of the Earth is cover by cirrus which has important impact on the balance of the energy budget,the evolution of climate and the change of weather.Therefore,all kinds of ways for the remote sensing of the cirrus has been studied by researchers all over the world,and THz wave is proved to be efficient for the remote sensing of the micro-physical properties of cirrus.The scattering properties of ice crystals in six different shapes has been calculated and studied based on the Discrete Dipole Approximation,so are the mean properties and the upwelling brightness temperatures of cirrus.Results show that the window frequencies under 300 GHz has great potential in the remote sensing of ice crystal whose largest size is 1100 ?m.3.The 340 GHz atmospheric propagation systems are calibrated,and the experimental data are analyzed comparing to theoretical results.The outdoor path of the 340 GHz atmospheric propagation systems is 300 m which is a long outdoor path at THz wave.The attenuation model at 340 GHz based on curve fitting of atmospheric attenuation is built and high accuracy is performed.Theoretical and experimental studies on 340 GHz atmospheric attenuation will provide powerful technical support for 6 G communications.4.The attenuation along Earth-space paths is one of the most important factors should be considered.And the attenuation by clear atmosphere is determined by the profiles of temperature,water vapor content and pressure which are quantities not easy to get.Equivalent height introduced in Rec.ITU-R P.676-11 is a model to estimate the path attenuation using meteorological parameters at the Earth's surface.However,this model cannot be applied to different areas and seasons because only pressure is included.Therefore,a new model is proposed by introduce temperature and water vapor content to the dry air equivalent height model and an additional parameter of columnar water vapor content to the water vapor equivalent height model.The new models are verified to be more accurate.Besides,some significant absorption peaks under frequencies of 1 THz are added to extend the application range to 1 THz.Digital maps of equivalent heights and zenith attenuations are calculated and analyzed,the zenith attenuation in northwest region of China are smaller than 20 dB in both January and July,2016,which indicates great potential in Earth-space communication.5.Frequencies near the absorption peak frequencies are important channels for the remote sensing of temperature and water vapor content,while window frequencies are always chosen for detecting.Using the radiative transfer theory,the radiation contribution variation with altitude under different profiles are calculated and compared based on the absorption equations introduced in Rec.ITU-R P.676-11 and the atmospheric profiles in Rec.ITU-R P.835-6.Channels for remote sensing of different altitudes are suggested.The background radiation at both window and peak frequencies are calculated and compared using Atmospheric Radiative Transfer Simulator.The brightness temperature decrease with altitude and become constant at altitudes higher than about 10 km at window frequencies.While at peak frequencies,the brightness temperature increase before it become constant because the significant attenuation to the radiation of lower atmosphere.The angle variations of the brightness temperature show that,at aircraft altitudes,the background radiation is smaller for window frequencies than that of peak frequencies,however,the distinctions are not significant at satellite altitudes.These analyses provide a basis for the future detecting applications.