Theoretical Research And Actual Measurement Of Wave Infrared Transmittance In The Atmosphere At Different Altitudes

Infrared technology has extremely important applications in the earth's surface and space fields such as night vision,missile guidance,space remote sensing,and astronomy.Because the earth's atmosphere absorbs and scatters infrared radiation,infrared atmospheric transmittance is an important factor affecting infrared target detection.In military aspects such as infrared night vision,observation and targeting,and infrared missiles,atmospheric infrared radiation is not only a strong "background",it also determines the intensity which the target radiation reaching the detector.In the design of infrared remote sensing systems,the atmosphere has two important optical properties: one is the transmittance of the atmospheric path between the radiation source and the receiver,and the other is the radiation intensity of the atmosphere.In astronomical infrared observations,atmospheric transmittance determines the location of large infrared telescopes.The earth's atmosphere is composed of many molecules,the main components of which are water vapor,carbon dioxide and nitrogen.The infrared transmittance of the atmosphere is mainly determined by the absorption of these molecules.Changes in the ambient temperature,pressure,and relative humidity at different altitudes on the surface of the earth will seriously affect the molecular composition,concentration,and other characteristics.In addition,the meteorological conditions of the atmosphere change at any time.It is of great significance to conduct theoretical research and real-time measurement.At present,the main ways to obtain atmospheric transmittance are theoretical calculation,software simulation and actual measurement.This article uses these three methods to study the medium-wave(4.605-4.755?m)infrared atmospheric transmittance at different altitudes.1.Firstly,the theoretical calculation method is discussed,In the calculation process,the atmospheric absorption and scattering are mainly considered,including the absorption of water vapor and carbon dioxide molecules,and the aerosol scattering effect.The water vapor and carbon dioxide transmittance are obtained by numerical fitting.Finally,the atmospheric transmittances of 4.6 ?m,4.7 ?m,4.8 ?m at altitudes of 5 km,3 km,and 0 km are obtained.The atmospheric transmittances at 4.6 ?m,4.7 ?m,and 4.8 ?m at 5 km are: 0.969,0.931,and 0.661.The atmospheric transmittances at 3 km are 0.915,0.836,0.451,and the atmospheric transmittances at 0 km are: 0.907,0.820,0.348.The weighted average method was used to obtain the average atmospheric transmittances of 4.605-4.755 ?m at three altitudes,which were 0.906,0.805,and 0.780,respectively.2.An actual measurement method was proposed to measure the atmospheric transmittance day and night.The atmospheric self-radiation is considered as the target,the infrared atmospheric transmittance is obtained through the monochromatic radiation transfer equation,and the measuring equipment is cooled to-40 ° C to reduce the instrument's spontaneous radiation.The calibration of infrared measuring equipment is researched.Based on the univariate calibration model,a ternary calibration model that separates the integration time and the ambient temperature is proposed.Its fitting correlation coefficient can reach 1.Finally,in three locations at different altitudes(Ali,Tibet,Delingha,Qinghai,and Huairou,Beijing),by measuring the atmospheric radiation at different zenith angles,the average atmospheric transmittance of 4.605-4.755 ?m was fitted.They are: 0.831,0.766 and 0.673.3.The MODTRAN commercial software was used to simulate the infrared atmospheric transmittance at altitudes of 5km,3km and 0km respectively.The simulation results are 0.848,0.796,and 0.691.The simulation results at three different altitudes are 2%,3.9%,and 2.3% higher than the actual measurement results,which can explain the feasibility and accuracy of the actual measurement.In addition,after separating the transmission caused by water vapor,carbon dioxide,ozone,and nitrogen absorption,it was found that water vapor absorption has the greatest effect on transmission.The daily precipitation water vapor in Ali at 5km above sea level is about 1.67 mm,while the amount of precipitation water vapor in Delingha is about 3.44 mm,and the precipitation water vapor in Huairou is about 2.16 mm.Because the amount of precipitation water vapor in Ali is much lower than Delingha and Huairou,its infrared atmospheric transmittance is significantly higher than the other two low-altitude areas.