Early Forest Fire Monitoring And Warning Method And Experimental Research Based On LiDAR Technology

Forest fires have the characteristics of being the most difficult to prevent and the fastest to spread in natural disasters.They pose a serious threat to people’s life and property safety,ecological environment,and social economy.Once a fire occurs,it is necessary to quickly respond and take firefighting measures.Whether it can be promptly extinguished and whether the government’s decision-making is appropriate mainly depends on whether the fire can be detected in a timely manner and provide correct analysis and decision-making,Therefore,the earlier a fire is detected,the earlier intervention can be implemented to minimize losses.Therefore,countries around the world prioritize early fire monitoring,early warning,and firefighting in the face of forest fires.Due to the high spatiotemporal resolution,wide detection range,and sensitivity to changes in aerosol concentration of LiDAR,it can be applied to the monitoring and warning of forest fires.Therefore,this article conducts research on early forest fire monitoring and warning methods based on LiDAR technology.On the basis of thorough research on relevant research progress at home and abroad,the paper focuses on the characteristics of smoke particles in forest fires from pyrolysis,smoldering to open fire.Starting from the light scattering theory and particle polarization characteristics,using the ability of polarized laser radar to distinguish particle morphology,a rapid-fire detection and early warning method is established in the smoldering stage.The paper proposes and conducts research on early forest fire monitoring and early warning methods using LiDAR.Considering that in the early stages of forest fires,when smoke is below the canopy and the concentration is low,the signals obtained from LiDAR monitoring contain information such as smoke,mountains,and vegetation,and the smoke information is submerged in strong background signals,a preliminary analysis of the early warning methods was conducted,And the waveform decomposition method and frequency domain analysis method were used to extract weak smoke signals from mixed signals.The analysis results showed that neither conventional LiDAR inversion nor waveform decomposition method or frequency domain analysis method could extract weak smoke signals from strong background signals,revealing the limitations of LiDAR in the early forest fire monitoring process.Due to the spherical characteristics of smoke particles during the smoldering stage of forest fires,and based on the similarity between smoke and haze,water mist and water cloud,a vertically oriented polarized LiDAR was used to detect haze and water cloud.The inversion results showed that the depolarization ratio of water cloud particles was around 0.05,and the depolarization ratio of haze particles was around 0.04-0.08,The results preliminarily verified the feasibility of polarization lidar monitoring forest fires from both theoretical and experimental perspectives.Finally,in order to reduce the problem of misidentification caused by smoke particles and water mist particles being spherical particles during the smoldering stage of early forest fires,a simulation experiment and measurement system for early forest fire scenes was designed and built based on the principle of polarization lidar.For different scenarios of early forest fires,simulation detection experiments were conducted under three different conditions: single smoldering smoke,single water mist,and a mixture of the two.The results showed that smoke,water mist,and the depolarization ratios of the mixed state range from 0.10 to 0.24,0.18 to 0.31,and 0.15 to 0.6,respectively,which are smaller than the depolarization ratios under empty background conditions;Analyzed the misjudgment rate of using the depolarization ratio to identify smoldering smoke warning.If the depolarization ratio is used solely as a means of identifying early fires,the probability of misjudging smoldering smoke as water mist is 28.57%,the probability of misjudging mixed state as water mist is 28.89%,and the probability of misjudging any form containing smoldering smoke as water mist is 26.00%.Based on the above analysis results,a preliminary warning strategy is proposed.