Research On On-line Measurement Technology Of Moisture Content Of Forest Dead Combustibles

Forest surface dead combustible moisture content directly affects the probability of forest fire occurrence and forest fire behavior.In order to solve the problem of on-line measurement of forest surface dead cornbustible moisture content,this issue was studied theoretically and experimentally with the support of the basic research and operation fee project of the Central University(2572017DB04).The main contents are as follows:Combining the infrared absorption spectra of water,in order to find out the relationship between the different moisture content of forest dead combustibles and the near infrared absorption spectra,the infrared spectrum characteristics of forest dead combustibles under different moisture content were analyzed by using optical fiber spectrometer.The results show that 1450 nm is the absorption peak of water,which verifies the feasibility of on-line measurement of forest surface litter moisture content based on infrared absorption spectroscopy.At the same time,it provides a basis for the measurement principle and the choice of infrared laser.In terms of device development,according to the principle of relative reflectance measurement method,an infrared reflectance measurement device consisting of STM32 embedded controller,infrared laser,semi-transparent semi-reflector,standard whiteboard and two infrared photodiodes is built.According to the component parameters,the photodiode amplifier circuit is designed,and the amplifier circuit is simulated by Tina-TI circuit simulation software.The amplified output voltage is connected to the I/O port of STM32 for A/D acquisition,and the output voltage indication of STM32 is calibrated by an oscilloscope.In order to realize the long-distance wireless transmission of measured data in forest land,LoRa long-distance wireless transmission module is adopted.The main control interface of the host computer is designed by LabVIEW.In water content calibration,two calibration experiments were completed to establish the accurate relationship between water content of forest dead combustibles and infrared reflectance.Because this device uses relative measurement method to measure infrared absorption spectral reflectance,it is necessary to make dead combustible powder to ensure diffuse reflection.The relationship between water content of dead combustible powder and reflectance of different forest stands is calibrated experimentally.Considering that the actual forest dead combustible material is large blade shape,the change rate ot water content of leaf and water content ot powder shape is changed.Therefore,the water content of different forest powders and natural leaves were calibrated.In practical measurelent,the on-line measurement system of forest dead combustible moisture content was placed in Fraxinus mandshurica sample plot in the experimental forest farm of Northeast Forestry University.The on-line measurement of surface dead combustible moisture content was carried out for 15 consecutive hours,and the on-line measurement results were compared with the weighing method.The results show that the on-line measurement device of forest dead combustible moisture content designed in this paper has realized combustibility.The uncertainty of long-distance on-line measurement of water content is 27.99%.The on-line measurement technology of forest dead combustible moisture content realizes the on-line monitoring of forest dead combustible moisture content,further improves the measurement technology of forest dead combustible moisture content,and provides a technical basis for improving forest fire risk grade prediction and prediction.