Study On Monitoring Technology Of Moisture Content Of Typical Tree Species In Northeast China Bsed On Time Domain Reflectometry

Water is an important component of standing tree and an important factor affecting the growth and development of standing trees.Whether it is to serve the rational management of forests and scientifie protection,or based on the consideration of efficient proeessing and utilization of wood,the real-time and accurate determination of the moisture content of trees(wood)is of great significance.Time domain reflectometry(TDR)is one of the dielectric constant methods compared to other water content measurement methods,the calibration equation between the electromagnetic wave propagation time and the moisture content of the TDR test results needs to be constructed in the laboratory in advance.TDR is the most promising technology currently.In order to improve the practical application ability of TDR to monitor the moisture content of typical tree species in Northeast China,we need to consider the influence of large temperature difference in Northeast China on measurement accuracy,study the feasibility of using a short probe insertion depth to reduce damage to standing trees,construct calibration equation for some typical tree species in Northeast China,use a software designed by MATLAB to show TDR‘s real-time test results,these studys could provide theoretical guidance and scientific basis for rapid?real-time?accurate?continuous monitoring of moisture content of typical tree species in Northeast China based on TDR method.In laboratory room,the electromagnetic wave propagation time data were tested by TDR method under different tree species(Birch,Fir,Populus)?different temperatures(30 ?,-2 ?,-20?)?different probe insertion depths(2cm,4cm,6cm,8cm)?different moisture content conditions.According to these data,we can analyze of the influence of temperature and probe insertion depth on TDR test results,construct the calibration equations ofAbiesfabri(Mast)Craid?Populus simonii Carr?Betula platyphylla Suk species;Based on MATLAB,the real-time display software of moisture content is designed and its main functions are introduced;Moisture content data of Populus simonii Carr and Betula platyphylla Suk were continuously measureed in outdoor conditions,the effectiveness of continuous TDR monitoring was verified by analyze the data.Main conclusions are as follows:(1)When the moisture content is constant,with the decrease of temperature,the electromagnetic wave propagation time of Abies fabri(Mast.)Craib and Populus simonii Carr is gradually reduced,and the influence of temperature on the electromagnetic wave propagation time is lower than the moisture content.It can be inferred from the measured data that the temperature difference of 10“C will lead to a moisture content test error of about 1%.The temperature difference in different seasons in Northeast China is huge,inversion models of Abies fabri(Mast.)Craib and Populus simonii Carr were constructed at different temperatures of 30?,-2 ? and-20 ?,respectively,these models'R2?0.99,which can be used in different seasons in Northeast China to improve test accuracy.(2)When the moisture content is constant,the electromagnetic wave propagation time of different Betula platyphylla Suk specimens measured by TDR increases with the insertion depth.At 4cm,6cm and 8cm probe insertion depth,the elecfromagnetic wave propagation time increases with the increase of water content,and has a good response to the change of moisture content.At the insertion depth of 4 cm,the constructed calibration equation has the best prediction accuracy and fitting accuracy,and can reduce the damage to the trunk of the standing tree.Therefore,It is feasible to use a short probe insertion depth,when measuring moisture content by TDR method.(3)The moisture content eal-time display software designd by MATLAB can realize the following three functions:?You can manually input the parameters of different tree species inversion models to ensure the versatility of all tree species.?It can display data such as electromagnetic wave propagation time>temperature?measurement time?moisture content in real time.?A line graph showing changes in moisture content over time can be displayed in real time,and the line chart can be saved.(4)The continuous monitoring results of the moisture content of Populus simonii Carr and Betula platyphylla Suk show similar laws,The water content changes consistently with time within one day,Since about 12:00,the water content has continued to decline slowly,at 7:00 and 8:00 the next morning,it began to gradually pick up.It is indicated that the TDR method can effectively reflect the change trend of the moisture content of the standing tree and can be used to continuously monitor the moisture content of the standing tree of different tree species.