Calibration of soil moisture sensing with subsurface heated fiber optics using numerical simulation

The heat pulse probe method can be implemented with actively heated fiber optics (AHFO) to obtain distributed measurements of soil water content (θ) by using reported soil thermal responses measured by Distributed Temperature Sensing (DTS) and with a soil‐specific calibration relationship. However, most reported applications have been calibrated to homogeneous soils in a laboratory, while inexpensive efficient in situ calibration procedures useful in heterogeneous soils are lacking. Here we employed the Hydrus 2‐D/3‐D code to define a soil‐specific calibration curve. We define a 2‐D geometry of the fiber optic cable and the surrounding soil media, and simulate heat pulses to capture the soil thermal response at different soil water contents. The model was validated in an irrigated field using DTS data from two locations along the FO deployment in which reference moisture sensors were installed. Results indicate that θ was measured with the model‐based calibration with accuracy better than 0.022 m3 m−3.

Raw project data is available by contacting [e-mail]

热脉冲探针法可通过主动加热光纤（AHFO）实现，以利用报告中的土壤热响应（由分布式温度传感技术DTS测量）及土壤特有的校准关系，获取土壤水分含量（θ）的分布式测量。然而，大多数已报道的应用均在校准于实验室中的均质土壤上进行，而在异质土壤中应用的低成本、高效的现场校准程序尚显不足。本研究中，我们运用Hydrus 2-2D/3-D代码定义了土壤特有的校准曲线。我们确定了光纤电缆及其周围土壤介质的二维几何形状，并模拟热脉冲以捕捉不同土壤水分含量下的土壤热响应。该模型在灌溉田中使用DTS数据进行了验证，数据来源于光纤部署沿线的两个位置，其中安装了参考湿度传感器。结果显示，基于模型的校准测量θ的精度优于0.022 m3 m−3。

原始项目数据可通过联系[e-mail]获取。