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Research On Differential Absorption Lidar For CO2 Sensing

Posted on:2016-12-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:H LiuFull Text:PDF
GTID:1108330479982331Subject:Circuits and Systems
Abstract/Summary:PDF Full Text Request
Carbon dioxide(CO2), one of the greenhouse gas, has gained increasing concern for its rapid growth since the late nineteenth century on the global scale. Identification of sink, source and flux of atmospheric CO2 can give important information about the climate change and related impacts on human beings.As an effective method for CO2 monitoring, differential absorption lidar(DIAL) has been studied by more and more countries. Therefor researching on the key issue that to establish the DIAL system for CO2 monitoring for our country is important. Firstly, the principle of DIAL has been described, and then the impact of the wavelength shift and the interference from water vapor has been analyzed. At last the relationship between the signal to noise ratio and systematic random error has been deduced. The lidar system was established based on the analysis on chapter 2, and a new method for calibrating the lidar system has been developed. CO2 concentration in Shanghai was recorded for several days, and the result showed that the trend of the DIAL was different from the in-situ CO2 sensor unless the status of atmospheric was stable.The innovation of the article was as following. Firstly, a new method for frequency offset locking which using time measurement was presented. The OFF-line laser was locked using a Fabry-Perot interferometer based on the pulse delay time measurement. A relative frequency fluctuation less than 0.1 MHz is achieved. Secondly, a more precise calibration method was developed which could simultaneously calibrate the offset and precision of the lidar detector. The result showed that a measurement precision of 0.525%(rms) for the column concentration was achieved in 1 s time interval. At last, diurnal variation of CO2 concentration was obtained, especially under complicated weather condition.
Keywords/Search Tags:differential absorption lidar, frequency offset locking, CO2 sensing, system calibration
PDF Full Text Request
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