| As a new detection method,terahertz detection technology has important research significance and broad application prospects in the field of spaceborne target detection.Aiming at the characteristics of terahertz atmospheric background radiation in Earth observation mode,this paper carries out a series of studies on the global clear-sky atmospheric background brightness temperature,sensitivity analysis and the effect of clouds on the atmospheric background brightness temperature,in order to provide background research basis and detection frequency selection scheme for spaceborne terahertz target detection.The main research contents of this paper are as follows:Based on the principle of radiative transfer,the atmospheric transmittance in terahertz band in typical areas is simulated by using the atmospheric radiative transfer model ARTS(Atmospheric Radiative Transfer Simulation),and the valuable window and absorption band are determined.According to the simulation results of transmittance,combined with ERA-interim(European Center for Medium-Range Weather Forecasting Re-Analysis-Interim)reanalysis data,the monthly average and a single day global clear-sky atmospheric background brightness temperature of window and absorption frequency band are simulated.The simulation results show that the atmospheric background brightness temperature in the absorption band is lower and evenly distributed than that in the window band.According to the differences of simulation results,different latitudes are selected for temperature and water vapor sensitivity analysis.It is determined that the reason for the difference is that the main contribution of the atmospheric background brightness temperature in the window frequency band comes from the troposphere with large changes of temperature and water vapor,and the absorption frequency band comes from the stratosphere with stable temperature and water vapor.Clouds are widely distributed near Earth’s surface,which is an important factor to study the characteristics of terahertz atmospheric background radiation.In order to study the effect of clouds on atmospheric background brightness temperature,clouds are divided into water clouds and ice clouds according to the phase state of clouds.On the basis of the particle scattering theory,the scattering characteristics of water droplets and ice crystals are simulated.Based on the clear-sky background brightness temperature,a control group was set up,and the effects of clouds on the atmospheric background brightness temperature under different conditions were analyzed by ARTS.The analysis results show that the positional relationship between cloud height and the sensitive height of detection frequency is the most important factor for the effect of clouds on atmospheric background brightness temperature. |
