Research On Specificity Enhancement Technology And System Design For Laser Remote Trace Gas Sensing

Due to the advantages of high sensitivity,fast response,in-situ online,non-contact and other advantages,laser remote sensing detection is widely used in the fields of detection of industrial exhaust gas,environmental sensitive gas,and hazardous chemicals.However,the detection or remote sensing for trace gas targets is often interfered by background gas and affected by environmental conditions,causing the target information to be aliased or even submerged.Therefore,the specificity enhancement technology and system design for laser remote sensing are studied in this paper.The main work of this article includes:Firstly,specificity enhancement technology for laser remote sensing based on interference measurement.In order to achieve high-sensitivity remote sensing of large molecular trace gases with broad-band spectral characteristics in the air,the specificity enhancement technology for laser remote sensing based on interference measurement is proposed.Noise removal,feature recognition,linear separation and inversion calculations on the absorption spectrum are performed to obtain accurate interference gas absorbance,ambient temperature and pressure,which are used for background interference reduction and environmental condition correction.The sensitivity of remote sensing for large molecule trace gas with broadband absorption characteristics is improved and its detection limit is lower.Secondly,the design of laser gas detection system.Two laser gas detection systems are designed and made:Hand-held ethanol gas remote sensor and engine exhaust online monitor,Specific work content includes:demand analysis for specific applications,demonstration of the overall plan,Specific design of optical path and mechanical structure,System assembling and debugging,as well as system working parameter optimization,etc.Thirdly,specificity enhancement verification and laser detection system performance evaluation.An ethanol gas calibration cell based on the principle of saturated vapor pressure is designed and made,which is used to solve the calibration and test for handheld ethanol gas remote sensor.Under laboratory conditions,the specificity enhancement technology and the performance of the handheld ethanol gas remote sensor were tested and verified.The test results show that in the mid-infrared(3.3μm)band,at least 33.0%of the background interference in the air can be eliminated,and the detection limit of ethanol vapor is reduced from 5.40 ppm to 1.87 ppm,which improves the detection sensitivity.System linearity is 0.981,and uncertainty is 4.2%.Specific parameters such as H2O,NH3 concentration,temperature,and pressure in the exhaust gas were specifically monitored at the engine working site.The relative measurement uncertainties were 8.4%,8.0%,5.3%,and 7.0%,respectively.The specificity enhancement technology proposed in this paper can effectively remove the background interference and noise in the air,greatly lowering the detection limit of remote sensing of trace gas in the air,and achieve simultaneous fitting and analysis of multiple measurement parameters in the spectrum lines to compensate for the interference effects,improving the sensitivity and anti-interference ability of remote sensing.There is important application value for the detection and discovery of environmentally sensitive substances,especially for the leakage of dangerous chemicals,terrorist attacks and chemical warfare that may endanger public safety.