The Development Of The In-situ Tester For Forest Litter Moisture Content

Forest litter is the most important function of forest ecosystem.In-situ determination of its moisture content plays an important role in the study of forest hydrological characteristics and forest soil respiration and carbon cycle.Besides,the forest surface combustibles are mainly concentrated on the litter layer,and its moisture content directly affects the difficulty and intensity of fire.Therefore,it is very important for forest fire monitoring and forest fire risk prediction to get moisture content of litter quickly and accurately.The litter layer has the characteristics of loose structure,high content of organic matter and thinner thickness compared with soil layer.And the change of compactness has great influence on the measurement of water content.The common soil moisture sensor is difficult to directly and accurately measure the moisture content of litter.According to the above characteristics,this paper proposes a measurement method of forest litter moisture content based on the principle of standing wave ratio(SWR)and design a sensor adapted to the measurement of forest litter moisture content.At the beginning of the paper,the related research on the measurement of water content in forest litter was introduced.Based on the principle of measurement,the measurement method suitable for forest litter structure was selected.The relative humidity method was used to determine the moisture content of the undecomposed layer.On the basis of laboratory experiments,the structure of the designed multiplexed double loop sensor probe is improved and optimized,and the water content and electrical conductivity of the forest litter can be measured in time.The experimental results show that the output voltage of the sensor has a good linear relationship with half decomposition,total decomposition litter and soil moisture content,and the fitting coefficient is over 0.96.Compared with the commercially available TDR(TRIME-PICO 64,IMKO,Germany)moisture sensor,the sensor developed in this paper measures the average absolute error of litter and soil moisture content is small,and has obvious advantages in the measurement of litter moisture content and measurement cost with a thickness of less than 10 cm.In the long-term in-situ determination of litter moisture content,The forest litter water content in situ measuring instrument can be judged by measuring the conductivity of semi decomposed litter is completely decomposed with time,and the compaction for reference variables to establish compactness and water content model,in order to adjust the sensor line calibration curve of moisture measurement,the maximum decrease due to the impact of litter changes in composition and litter density changes caused by the sensor measurement precision,accurate measurement of forest litter moisture basis.