Evaluating three measurement methods of soil ground heat flux based on actively heated distributed temperature sensing technology

Soil ground heat flux (G0) is a key parameter in analyzing soil-atmosphere interaction. It is not only an indispensable component in the surface energy balance, but also an essential boundary condition in the coupled hydro-thermal-mechanical (HTM) numerical analysis of soil-atmosphere interaction. In this study, three G0 measurement methods (gradient method, calorimetric method and combination method) are evaluated based on the measurements (temperature, volumetric water content and thermal conductivity) using the actively heated distributed temperature sensing (AH-DTS) technology. In addition, through a series of in-situ tests, the feasibility of these methods is verified, and their applicability and application potential are compared and analyzed. The results indicate that the G0 values measured by the three AH-DTS technology-based methods are in the same order of magnitude, indicating that the three methods are feasible. Among them, the G0 measured by the gradient method is an instantaneous value which is closely related to the soil surface water content, while the G0 measured by the calorimetric method and combination method is an average values over a period of time. The gradient method is applicable for all types of soil, including the frozen soils. The calorimetric method and the combination method are suitable for soils of which water content can be measured by the AH-DTS sensor. It is recommended that an appropriate G0 measurement method based on the AH-DTS technology be selected according to the site situations.