基于驻波率原理的森林枯落物和土壤含水率测量方法

Measurement Method of Forest Floor and Soil Water Content Based on Standing Wave Ratio

枯落物含水率测定在森林水文学、碳循环、林火蔓延以及火险等级评估等研究中具有重要作用。本文提出了一种基于驻波率(SWR)原理的森林枯落物含水率测量方法,所设计的SWR水分传感器具有复用双环式探头结构,可分时测量枯落物或土壤的含水率和电导率。实验结果表明,传感器输出电压与半分解、全分解枯落物和土壤含水率呈现良好的线性关系。与商品化TDR水分传感器相比,SWR传感器测量枯落物和土壤含水率的平均绝对误差较小,且在厚度小于10 cm的枯落物含水率测量以及测量成本方面具有明显优势。在对枯落物含水率进行长期原位测定时,SWR传感器可通过测量电导率判断半分解的枯落物是否随时间推移而完全分解,以便及时调整传感器水分测量的标定曲线,最大程度降低因枯落物成分改变对传感器测量精度造成的影响,为准确测量森林地表枯落物含水率奠定基础。

Forest floor moisture measurement plays a significant role in the research of forest hydrology,carbon cycle,forest fire spread and risk evaluation. A detection method of forest floor water content based on standing wave ratio（ SWR） was introduced. The developed SWR sensor with two parallel anular probes could measure the water content and electrical conductivity in forest floor or mineral soil by using time-sharing multiplexing technology. Experimental results showed that the relationships between the output voltage of SWR sensor and the water content of partly decomposed forest floor,well decomposed forest floor and mineral soil were linear,respectively. Compared with the commercial TDR sensor,the SWR sensor showed a better performance with smaller mean absolute error and lower cost in the measurement of forest floor and soil water content. In addition,the SWR sensor had obvious advantages when the forest floor layer was thin（ 10 cm）. It was notable that the partly decomposed forest floor might be decomposed completely in the long-term in situ moisture measurement. Therefore, the developed sensor estimated the decomposition rate by detecting electrical conductivity of forest floor,which would lay a foundation for the accurate measurement of forest floor water content.