Key Technologies Of All-Solid-State Na Lidar For Temperature And Wind Measurements

High-resolution detection of middle and upper atmosphere temperature and wind is one of the research hotspots in the field of atmospheric sounding and space physics.Temperature and wind detection in the mesopause region can be realized by using narrowband sodium Doppler lidar,which is an important observational means for space environment monitoring and prediction,atmospheric science research,and providing a key source of data for research on atmospheric wave propagation,momentum and energy cycle,high and low atmospheric interaction and other cutting-edge scientific problems.In this thesis,the key technologies of all-solid-state sodium lidar system for the mesopause temperature and wind measurements are discussed,and the temperature and wind measurement principle,lidar system design and implementation,data processing and retrieval method,and the preliminary observation results of sodium layer temperature and wind are described in detail.The main contents of this thesis are as follows:(1).The all-solid-state sodium lidar with the international advanced level for temperature and wind measurement was successfully developed.The laser system is based on sum-frequency mixing using solid-state lasers.Two seed lasers are utilized to output single-mode narrow linewidth continuous wave(CW)laser light at 1064 nm and 1319 nm,respectively,which are injected into two Nd:YAG pulse lasers and carry out sum-frequency generation(SFG).Finally,high-power 589 nm pulse laser source which can effectively excite sodium atoms in the mesopause region is obtained;an all-fiber-coupling seed injection unit is designed,laser frequency stabilization and shifting are designed with modular design using optical fiber transmission,greatly reducing the optical adjustment;589 nm CW narrow linewidth laser is generated by sum frequency of two CW seed laser light,and by making use of sodium saturation absorption spectrum and digital intelligent feedback control of 1064 nm and 1319 nm seed lasers,the sum-generated 589 nm CW laser frequency is locked to Na D2a transition peak for a long term;using fiber-coupled acousto-optic frequency modulation technology,together with optical switch control design,automatic cycle operation through three different laser frequency is achieved.In addition,the frequency shift amount is optimized by calculating the longitudinal mode spacing of 1064 nm Nd:YAG pulse laser cavity,effectively improving the reliability of injection seeding for three operating frequencies.The pulsed 589 nm laser beam is divided into three branches emitting in three different direction,and synchronous data acquisition for three detection direction is implemented.Remote control software platform for two-dimensional laser beam direction adjustment is designed,improving the automatic level of the system and the matching precision;data acquisition and system control software is developed for multi channel synchronous data acquisition,storage,real-time display,timing control etc..(2).The study of data processing and retrieving method for temperature and wind measurement is carried out.The preprocessing procedures for echo signal include abnormal data rejection,integration in time,background subtraction,power normalization and smoothing in height etc..The calculation method of temperature and wind ratios based on three-frequency ratio technology is given,and the basic processing procedures of retrieving temperature and radial wind using the ratios and the theoretical 2D calibration curve is described in detail,and the methods of radial wind calibration and horizontal wind synthesis are also given.We analyze the main error sources of temperature and wind measurement,including the system error caused by hanle effect,optical pump effect,saturation effect and laser frequency deviation,and the random error induced by photon noise,and give the calculation method of temperature and wind measurement accuracy.(3).Observation campaigns of temperature and wind in mesopause region was carried out using the developed all-solid-state sodium lidar system.Based on the two night temperature observations results in September 19 and 20,2016,a comparative analysis was made on the temperature of the sodium layer in two successive nights,indicating the obvious diurnal variations.The temperature results measured by the lidar are compared with the temperature data from satellite,and good agreement can be seen.The horizontal wind results measured by the lidar are compared with that of the meteor radar which has geographical proximity,and their variation trends with altitude and time are basically coincident.Compared with the meteor radar,wind measurement using lidar is more sensitive to gravity wave disturbance of small scale,so the wind profies of the lidar show more wave structures,while the results of the meteor radar change more smoothly with altitude.The horizontal wind evolution results with time of both instruments show downward phase propagation structures of tidal wave,whose wavelength scale level is bigger than the measured atmospheric space scale of both instruments and the tidal fluctuation can be detected by both instruments.The comparison and analysis of the temperature and horizontal wind results demonstrating the stability and reliability of the all-solid-state sodium lidar system.