The Research Of Signal Merge Based On The Differential Absorption Lidar System

Since the sixties of the eighteenth century,the rapid development of the industrial revolution led to a sharp increase in the use of fossil fuels,coupled with the degradation of forests caused by human activities,resulting in a large number of carbon resources that were originally confined to lithosphere and biosphere,mainly in the form of carbon dioxide Was released into the atmosphere,thus destroying the original stable carbon circulation system on Earth.Carbon dioxide has a strong absorption effect on the surface radiation of the hot infrared band and the solar radiation in the infrared and ultraviolet bands,and is a positive radiative forcing factor,which determines that it is a greenhouse gas.Studies have shown that the global average temperature rise and atmospheric carbon dioxide concentration increase has a very large correlation,so scientists believe that carbon dioxide is the world Rising temperatures,climate change and extreme weather factors.China in order to cope with the risks caused by climate warming,vigorously develop accurate detection of atmospheric carbon dioxide concentration change technology for the future introduction of the relevant low-carbon policy to provide scientific basis and protection.So far,atmospheric carbon dioxide concentration detection can be divided into two methods.One is active measurement,the other is a passive measurement.Passive remote sensing,that is,remote sensing system itself does not have a radiation source detection system,in the detection,the sensor mainly to obtain and record the atmosphere itself to launch radiation due to the heat radiation or other natural radiation sources?such as the sun?.Although there are many ways to detect,but it is subject to a variety of external conditions and internal defects,resulting in can't get high-precision measurement results.Active remote sensing,that is,within the detection system,comes with artificial radiation source,the use of artificial radiation source to the target to launch a specific wavelength of laser,so when the laser reaches the target,it will return an echo signal after scattering or reflection effect etc.,and then the sensor receives and record the target echo signal.The main atmospheric carbon dioxide concentration active detection method is differential absorption lidar,with high precision detection,by the external environment is small,the laser beam energy stability and other advantages.The study of this paper relies on a foundation of carbon dioxide differential absorption lidar system,mainly to detect low altitude?less than 3000 meters?atmospheric carbon dioxide column concentration information.Using the differential absorption lidar to measure the concentration ofcarbon dioxide in the process of information,the receiving system to collect echo signals are mainly in two forms,one is the simulation acquisition mode,one is the photon counting acquisition mode.The photon counting signal is mainly used for the detection of weak signals,with good noise suppression performance.Therefore,the signal-to-noise ratio?SNR?of the photon counting signal is better than that of the analog signal.However,due to the low-level signal,the photon counting signal at low altitude?less than 1000 m?There is a saturation effect,so the low-level photon counting signal is invalid.The analog signal is mainly used for strong signal detection,its high-altitude?higher than 1800 meters?signal SNR is very low,often buried in the noise,so the analog signal high-altitude signal is not available.Therefore,it is necessary to merge the analog signal and the photon counting signal to calculate the continuous column concentration information of carbon dioxide in the low-level atmosphere.Based on the above problems,this paper has conducted investigation and research.Many researchers have studied the radar echo signal merge problem,but due to various factors?splicing interval selection,signal nonlinearity,etc.?,these studies do not suitable for the ground-based carbon dioxide differential absorption lidar system echo signal merge.Therefore,according to the characteristics of the carbon dioxide echo signal of the differential absorption lidar system,this paper proposes to deal with the echo signal using the best uniform approximation theory.First,after the simulation experiment processing,the feasibility and applicability of the proposed method are proved.Then,in the analysis and discussion of the actual measurement signal,the signal merge method of Licel signal acquisition system is compared,which further confirms the advantages of the method proposed in this paper.Finally,the carbon dioxide column concentration information in the low-altitude atmosphere calculated by the merge signal is compared with the results of the in-situ measurement?EC9820 Carbon dioxide analysis,installed in the National Key Laboratory of Wuhan University for Surveying and Mapping Remote Sensing Information Engineering?,is also illustrate that the proposed signal merge method is helpful to improve the inversion accuracy of CO₂ concentration.