基于随机森林的电容式土壤水分传感器校准研究

Calibration of capacitive soil moisture sensor based on random forest

土壤含水量信息对于自然生态修复、农田灌溉管理、土体工程建设等具有重要的意义,电容式土壤水分传感器是获取该信息的主要途径之一。为准确校准电容式土壤水分传感器(以5TE设备为例)的土壤含水量观测数据,开展了不同温度、含盐量、土壤含水量条件下的土壤介电常数、电导率和温度观测实验,构建了基于随机森林机器学习方法的土壤含水量估计模型。结果表明:①变温、变含盐量情况下,土壤介电常数受含盐量和温度影响显著,仅基于土壤介电常数的传统土壤含水量估计模型失效;②以电容式土壤水分传感器观测的土壤介电常数、电导率和温度数据为输入,基于随机森林机器学习方法的土壤含水量估计模型可有效改善土壤含水量估计结果(RMSE为0.05 m^(3)/m^(3),R^(2)为0.77;修正Topp公式的土壤含水量估计结果:RMSE为0.07 m^(3)/m^(3),R^(2)为0.54);③土壤电导率观测对土壤含水量估计最为重要,介电常数次之,温度最弱,但均未达到可忽略不计的程度。研究成果可为电容式土壤水分传感器在变温、变含盐量地区的成功应用提供支撑。

[Objective]Soil moisture information crucial for various applications,such as natural ecological restoration,farmland irrigation management,and soil engineering construction.One of the main sensors used to obtain this information is the capacitive soil moisture sensor.[Methods]To accurately calibrate the soil water content observation data of the 5TE capacitive soil water sensor,soil dielectric permittivity,electric conductivity and temperature observation experiments were carried out under different temperature,salt content and soil water content conditions.A soil water content estimation model based on the random forest machine learning method was established.[Results]The results showed that:①The soil dielectric permittivity was significantly affected by varying salinity and temperature with constant soil water content.The traditional soil water content estimation model based only on soil dielectric permittivity became invalid,②The soil water content estimation model based on the random forest method could effectively improve the soil water content estimation with the soil dielectric permittivity,electric conductivity and temperature data as input.Random forest method obtained soil moisture estimation with RMSE=0.05 m^(3)/m^(3) and R^(2)=0.77,while RMSE=0.07 m^(3)/m^(3) and R^(2)=0.54 were obtained by the modified Topp equation,and③The soil electric conductivity was the most important factor for soil water content estimation,followed by the dielectric permittivity and temperature.Nevertheless,the importance of the dielectric permittivity and temperature did not reach a negligible level.[Conclusion]This study provides a way to support the successful application of capacitive soil moisture sensors in areas with variable temperature and salinity.