| Differential absorption lidar (DIAL) system can be used to accurately detect theatmospheric concentration of trace components. It is a main means anddevelopment trend of monitoring for spatial and temporal distribution of greenhousegases. The research on related technologies of ground-based DIAL system willprovide a reference for further research and application, as for airborne detection.The domestic and international developments of the atmospheric lidar systemare introduced, firstly. Based on the fundamentals of DIAL system to detecting theatmospheric concentration of trace components, the lidar equation ofcontinuous-wave (CW) DIAL system is induced. Both the hardware and softwareblock diagram of the amplitude-modulated (AM) CW DIAL system is presentedwhich aims to satisfy the requirements for detection of the CO2distribution in thelower troposphere.The key techniques of continuous-wave (CW) DIAL that are different fromthose of pulsed-wave (PW) DIAL were discussed. The main contents are: a) Theselection and the evidence of related parameters in CW DIAL, such as differentialwavelengths, modulation frequency, data acquisition, etc. b) The comparison of threeinversion methods due to different averaging/rationing orders and their impaction onthe CW system. c) The improvement limitation of standard deviation of the ln(ratio)through signal cumulative averaging in CW system. And the results showeddepartures from theoretic N-1/2dependence improvement.Moreover, the noise and error theory of DIAL system is analyzed. And aresolution estimate method was proposed, which showed a resolution of CO2concentration to <1.1%standard deviation in our DIAL system.Finally, a functional verification on each unit of the system was developed. Andthe diurnal variation of CO2concentration in the urban district of Shanghai waspresented with a contrast of data from LI-7500A CO2/H2O analyzer. The experimentresults show that the system is stable and reliable. |
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