宇宙射线中子法测量土壤水分的原理及应用

Principles and Application of Cosmic-ray Neutron Method for Measuring Soil Moisture

宇宙射线中子法是目前测定区域土壤水分较为先进的方法,具有便利、准确、无污染的特性,能够连续、自动地监测半径300 m范围内土壤水分动态变化。目前只有美国Hydroinnova公司进行了宇宙射线中子仪的研发与生产。文章介绍了宇宙射线中子法的工作原理及其在北京郊区的实地安装、使用,并对影响其测量准确性的相关因素进行了分析。试验结果显示,宇宙射线中子法所计算出土壤水分值与土样计算出的水分值之间的均方根误差和R2分别为0.011 kg/kg和0.71,而经气压和水汽修正前,两者的均方根误差和R2分别为0.022 kg/kg和0.313。表明宇宙射线中子法能够准确、灵敏地感应源区内下垫面土壤水分的变化,且在应用过程中,有必要对气压和空气水分的影响做出修正。

Cosmic-ray neutron method characterized by convenience, preciseness and pollution-free, is one of the most advanced methods to quantify soil moisture at the plot scale. It is able to monitor soil moisture fluctuations in an area of a circle of 300 m in radius. So far, the Hydroinnova, LLC of Albuquerque in US is the only company which is carrying on the research and manufacture of cosmic-ray neutron probe. The author introduced theories of cosmic-ray neutron method, as well as the installation and application of cosmic-ray neutron probe at the suburb of Beijing. In addition, relative factors, which might affect the measurement accuracy of the method, were analyzed. Experimental results showed that： the RMSE and R2 of the soil moisture that derived respectively from cosmic-ray neutron method and oven-drying are 0.011 kg/kg and 0.71, however, before the correction of pressure and atmospheric water vapor, the numbers are 0.022 kg/kg and 0.313. It was demonstrated that cosmic-ray neutron method could sense the fluctuation of the underlying surface soil moisture in the source region accurately and sensitively. In the application, it was necessary to correct the temporal changes of pressure an atmospheric water vapor.