Feasibility of soil moisture estimation using passive distributed temperature sensing

Through its role in the energy and water balances at the land surface, soil moisture is a key state variable in surface hydrology and land‐atmosphere interactions. Point observations of soil moisture are easy to make using established methods such as time domain reflectometry and gravimetric sampling. However, monitoring large‐scale variability with these techniques is logistically and economically infeasible. Here passive soil distributed temperature sensing (DTS) will be introduced as an experimental method of measuring soil moisture on the basis of DTS. Several fiber‐optic cables in a vertical profile are used as thermal sensors, measuring propagation of temperature changes due to the diurnal cycle. Current technology allows these cables to be in excess of 10 km in length, and DTS equipment allows measurement of temperatures every 1 m. The passive soil DTS concept is based on the fact that soil moisture influences soil thermal properties. Therefore, observing temperature dynamics can yield information on changes in soil moisture content. Results from this preliminary study demonstrate that passive soil DTS can detect changes in thermal properties. Deriving soil moisture is complicated by the uncertainty and nonuniqueness in the relationship between thermal conductivity and soil moisture. A numerical simulation indicates that the accuracy could be improved if the depth of the cables was known with greater certainty.

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

土壤湿度，通过其在陆地表面能量和水平衡中的作用，成为地表水文学和陆地-大气相互作用中的关键状态变量。利用诸如时域反射ometry和重力采样等成熟方法，土壤湿度的点观测相对简便。然而，使用这些技术监测大规模的变异性在物流和经济上均不可行。在此，我们将引入被动土壤分布式温度传感（DTS）作为基于DTS测量土壤湿度的一种实验方法。在垂直剖面中，使用多根光纤电缆作为热传感器，测量由于昼夜循环引起的温度变化传播。当前技术允许这些电缆的长度超过10公里，而DTS设备则允许每1米测量一次温度。被动土壤DTS的概念基于土壤湿度影响土壤热性质的事实。因此，观察温度动态可以提供关于土壤湿度含量变化的线索。本初步研究的结果表明，被动土壤DTS可以检测热性质的变化。由于热导率与土壤湿度之间关系的不确定性和非唯一性，从土壤湿度中提取信息变得复杂。数值模拟表明，如果能够更准确地知道电缆的深度，则可以提高准确度。

原始项目数据可通过联系[e-mail]获取。