Research On 935nm Differential Absorption Lidar For Atmospheric Water Vapor Measurement

Atmospheric water vapor has a great influence on the climate and plays an important role in many physical and chemical processes in atmosphere. Besides, water vapor involves in the formation of aerosol and cloud in troposphere, and it’s concentration varies with region, season and height. Therefore, instruments measuring concentration profiles of atmospheric water vapor with high accuracy and high temporal-spatial resolution are highly desired for weather and climate researches. Among these instruments, the differential absorption Lidar(DIAL) is a highly valuable observation tool for water vapor measurement.The major work in this dissertation is focused on DIAL technology for atmospheric water vapor measurement including the numerical simulation and the development of a ground-based DIAL system. This work have paved the way towards practical applications in the future.In the simulation part, errors in concentration measurement are analyzed. The performances of a DIAL for atmospheric water vaper measurement in different seasons utilizing three different absorption lines around 935 nm are simulated according to the climate of Shanghai. The results show that 935.906 nm should be employed as the on-line wavelength in summer while 935.776 nm performs better in winter. In the experiment part, the detail design of our 935nm-DIAL system is demonstrated, and a novel frequency stabilization method for the pulse OPO is proposed, by which the standard deviation of less than 30 MHz is achieved enabling good performance of the DIAL. Moreover, Lidar signal processing algorithms are researched and related softwares based on Lab VIEW are also developed for real-time concentration inversion and long-term data recording.. Water-vapor profiles in convective boundary layer of Shanghai are obtained by our DIAL, the statistical errors are less than 0.1g/m3 from 600 m to the top of convective boundary layer with a range resolution of 30 m and a time resolution of 60 s during both daytime and night. Comparisons between our measured data and those of the radiosonde measurements from the nearest meteorological station show good validity of our DIAL results.