Research And Implementation Of A Remote Impedance Monitoring System For Living Trees Based On LoRa

China has a vast territory and forest area.The health of the forest living tree ecosystem is an important concern for ecological protection.The health evaluation of wild living tree is usually only judged by appearance,with poor accuracy and timeliness.The impedance value of living tree,as one of the electrical characteristics of them,has intuitive and reliable measurement results,which provides a new development idea for fast and efficient diagnosis of tree vigor.At the same time,the management mode of forest living tree is mostly manual on-site operation,and the degree of informatization and digitalization needs to be improved urgently.In order to improve the detection accuracy of forest living tree impedance value,enhance the detection efficiency,reduce the human workload,and expand the degree of digital automation and informatization,a remote impedance monitoring instrument for living tree based on LoRa has been designed.For the first time,AD5933 impedance measurement module was used to detect the resistance of forest living tree,which expanded the measurement channel and improved the detection accuracy.The data transmission was carried out by SX1276 transmission module,which has long transmission distance and low power consumption,and can monitor the impedance of living tree remotely for a long time.The specific research contents are as follows:(1)A set of living tree impedance measurement instrument was designed and manufactured based on STM32F103 main control chip and AD5933 measurement chip,;uC/OS-Ⅲ real-time operating system was transplanted into single-chip microcomputer system,and STem Win tool was used to design graphical interface for LCD screen to complete human-computer interaction during offline measurement.The impedance testing system has completed the collection of impedance data.After comparing with high-precision impedance measurement instrument,it was concluded that the measurement error of the system was within 0.5%,and the measurement channel was expanded to 32 channels.(2)A LoRa long-distance transmission node was designed using the STM32L151 main control chip and SX1276 communication module..Based on MT7628 main control chip and SX1301 communication module,a set of LoRa gateway device was designed under Linux operating system;The software design of the gateway upper computer was carried out using MATLAB,achieving the reception of remote impedance data and the sending of remote control commands;The gateway and nodes form a LoRa WAN network,with a signal transmission range of up to 3km and a packet loss rate of as low as 0.03% for data transmission.(3)Utilize the LoRa node and gateway to indicate the received signal strength based on the LoRa signal obtained by the gateway.The analysis of the Received Signal Strength Indicator(RSSI)selected relevant forestry feature parameters for data combination,and modeled and analyzed the transmission characteristics of 470 MHz signals in mixed forests.By optimizing the parameters of random forest,we found the parameter values that best suit 470 MHz channel propagation model.The optimized random forest algorithm finally improved the determination coefficient of modeling to 0.928 and reduced the root mean square error value to 3.17.The model has good fitting effect and high stability.(4)On the premise of debugging and error analysis experiments of remote standing tree impedance tester,adjusting the measurement parameters and ensuring the optimal use performance of AD5933 impedance measurement chip,long-term data collection and monitoring were carried out using the remote standing tree impedance tester,and the impedance characteristics of several representative tree species in the subtropical monsoon climate region of the lower reaches of the Yangtze River in southeast China were obtained.During the annual cycle from 2022.01 to 2023.01,the impedance values of healthy living wood samples showed similar and stable seasonal changes.The impedance value of healthy samples rapidly decreased from January to May 2022,reaching a low point from June to August,and the impedance value was the lowest in August;The impedance values of healthy samples increased rapidly from September 2022 to January 2023,with January having the highest impedance value;In a rotation period of the earth(24 hours),the peak value of the resistance of healthy standing trees appears between 14 and 16 hours,and the valley value appears between 5 and 7 hours.It was found that the impedance value of the xylem of living trees remained at the K Ω level,the impedance value of coniferous trees was higher than that of hardwoods,and the increase and decrease mutation rate of the impedance value of coniferous trees was less than the increase and decrease mutation rate of the impedance value of hardwoods.This design provides a scheme for remote monitoring of living tree impedance.The design has high detection accuracy and efficiency,multiple measurement channels,greatly reduced monitoring cost,and provides assistance for the health monitoring of living tree.