Research On Fire Forest Early Detection Technology Based On TDLAS Method

As a huge resource treasure and one of the important living environments in biosphere,forest plays the role of preventing sand wind,purifying air,protecting water,keeping off water and soil loss,and maintain atmospheric balance.However,forest fire has become the most serious disaster in forest.For this reason,how to realize early detection,accurate positioning and instant alarm of forest fire has always been the hotspot and difficulty of forest fireproofing technicians' researches.Considering the detection ability of traditional forest fire monitoring method is insufficient because of small smoke,heat and radiation energy generated in early stage of forest fire,the research on forest fire earlier detection technology based on tunable semiconductor laser absorption spectroscopy is proposed.The model of gaseous emission early in forest fire is constructed and TDLAS(tunable diode laser absorption spectroscopy)trace gas test method is adopted to instantly detect and monitor CO concentration variation trend are adopted and realize early detection of forest fire.Meanwhile,the method raised is verified through simulating combustion test.The specific research is as follows:(1)The combustion of forest combustible generally consists of heat absorption,thermal decomposition,mixture,and combustion action.Based on the simulated combustion experiment of Mudanjiang Shaungfeng Forestry Station,this paper researches the combustion mechanism of forest fire and the gas emission in pyrolysis of early forest fire.By means of constructing the model about flow characteristic of gas emission as well as distribution early in forest fire,and analyzing experimental data,the new thought and method based on TDLAS trace CO gas monitoring is proposed for early detection of forest fire.(2)Through analyzing and researching TDLAS trace gas detection principle,CO gas absorption line selection,lock-in amplifier technology and secondary harmonic signal extraction,the closed-loop control of DFB laser,electricity and temperature is finished based on negative feedback and PID algorithm,which enhances wave length control precision;the micro optical gas chamber is designed through the advanced molecular sieve technology of self-focusing lens,so as to improve stability of measuring gas concentration;the design of digital orthogonal lock-in amplifier on foundation of FPGA is presented to greatly increase SNR extracted by optical weak signal,which provides reliable data source for subsequent gas concentration inversion.(3)Through profound research on modulation,modulation frequency,scan signal amplitude,harmonic signal amplitude as well as other control parameters of TDLAS-based CO gas detection system early in forest fire,and harmonic wave optimization,the influence of phase difference,time constant and sensitivity in lock-in amplifier on detection result is analyzed to render the multi-factor parameter optimization strategy based on optimal SNR,which can further improve SNR of detection signal.(4)During the process of measuring trace CO gas concentration early in forest fire,the sensitivity and detection precision of TDLAS,so the analysis and research on influence mechanism are carried out.Therefore,TDLAS calibration model and calibration factor analysis are built up,and the L-M algorithm based interference noise restraining method as well as temperature compensation method of zero point based on characteristic compensation are put forward.All these enhance system detection precision.The forest fire early detection method,presented in this paper,is verified via simulating combustion test in Mudanjiang Shaungfeng Forestry Station,which shows that,this method can realize early detection and warning of forest fire with certain reference value as well as promotion significance to early detection of forest fire.Thus,it will further facilitate the progress of Chinese forest fire prevention technology.