Observing And Studying The Near Space Atmosphere By Ground-based Lidar

In recent years,the atmospheric layer in the altitude range of about 20-100km is called the near space layer by aeronautical and astronautical communities.And the unique resources superiority of the near space has attract a lot of attention and focus by many countries.So researches and explorations on the near space atmosphere are of great important significance.At present,Rayleigh Lidar based on Rayleigh scattering principle,has been widely used for measuring the near space atmosphere with reasonably high accuracy.Rayleigh Lidar can provide continuous observational data with high spatial and temporal resolution,which is very essential for understanding the near space atmospheric structure and trends.The Rayleigh Lidar,located in one part of northwest China by Anhui Institute of Optics and Fine Mechanics,was successfully construct to measure the atmospheric variations of near space atmosphere.In this paper,the Rayleigh Lidar is evaluated.The retrieved algorithm of Lidar is studied.By the routinely Rayleigh Lidar observation,the near space atmosphere ranging from 20-40km over observation site is studied.The studying results as follow:The Rayleigh Lidar system is described,which adopts Nd:YAG laser of 532nm and 400mm Cassegrain telescope,and can be used to measure near space density,pressure and temperature at night.Using this 532nm Rayleigh Lidar,we measured and analyzed the atmospheric density profile,pressure profile and temperature profile from 20-40km over observation site.By comparing Rayleigh Lidar measurements with the data provided by NRLMSISE-00 Atmosphere Model and US standard atmosphere model(USSA 1976),radiosonde and FY-3C satellite observations,their good agreements indicate that Rayleigh Lidar measurements and data analysis are reliable.The errors in the inversion algorithm and the influence of the errors on the inversion accuracy are analyzed.The effects of ozone and aerosol on the inversion results,the statistical errors of the system and the error caused by the reference parameters are analyzed.And the accuracy of Rayleigh Lidar that effected by the data of reference point is focused on.It can be found that there is big bias between the inversion results from two different reference models,and there is nearly no bias between the atmospheric density and pressure inversion results from different reference height in the same reference model.However,it can found the bias between the atmospheric temperature inversion results from different reference height in the same reference model.In order to detect the weak backscatter return signal of near space atmosphere and improve the stability and SNR of Rayleigh Lidar,the 532nm Rayleigh Lidar system is updated.And the numerical calculation method of reference points is optimized to reduce the uncertainty of the initial value of atmospheric density.355nm Rayleigh Scattering Lidar system which is improved on the basis of 532nm Rayleigh Scattering Lidar system,employs Nd:YAG laser of 355nm and four Cassegrain telescopes of 400mm for the first time in China.According to experimental comparison,it could obtain that the SNR of 355nm Rayleigh Scattering Lidar is higher than 532nm Rayleigh Scattering Lidar of about 6 times.The fluctuation of the density ratio and pressure ratio of 355nm Rayleigh Scattering Lidar to Sounding Balloon are less than the fluctuation of 532nm Rayleigh Scattering Lidar.The temperature biases between 355nm Rayleigh Scattering Lidar and the sounding balloon of that day are about-2.14K,and the temperature biases between 532nm Rayleigh Scattering Lidar and the sounding balloon of that day are about-6.98K.The results of comparative test for 355nm Rayleigh Scattering Lidar and 532nm Rayleigh Scattering Lidar have shown that the detection precision of 355nm Rayleigh Scattering Lidar was higher than 532nm Rayleigh Scattering Lidar.The near space atmospheric density,pressure and temperature structure have been measured by 532nm and 355nm Rayleigh Scattering Lidar nearly one year between the altitude 20 km and 40 km at observation site,respectively.And there are effective observations about 7247 times,which distribute more than 280 days.According to the observational data of the Rayleigh Lidar from March 2015 to February 2016,the near space atmospheric yearly density,pressure and thermal structure(20-40km)was obtained.Lidar observation results showed the atmospheric temperature from May to August over observation place is higher than the others over the observation site from 20 to 40km.There are temperature fluctuations from May to August and in January about 30-40km,and temperature fluctuated greatly from March to April about 20-25km.Results show that atmospheric density distribution is sparse from December to February next year.Lidar atmospheric density observation results showed a characteristic upwards disturbance in 36-37km from May to September and a characteristic downwards disturbance in 26km from September to December.The results also show that atmospheric pressure distribution over the observation site is relatively low from December to February next year.The yearly distribution of atmospheric pressure seems to be relatively stable over 35km.From 20km to 35km,the atmospheric pressure is higher than the annual average of pressure in summer and autumn,and the atmospheric pressure is lower than the annual average of pressure in winter and spring.Based on the observation results of Rayleigh Lidar,the near space atmosphere model of the observation site is preliminarily presented in this thesis.Through the long-term observation of the near space atmosphere over observation place by our Rayleigh Lidar,we can obtain the measured data,which could form the atmospheric parameter database of the near space in observation place,forecast the near space weather and establish Middle and upper atmosphere model of China.