A DISTRIBUTED HEAT PULSE SENSOR NETWORK FOR THERMO-HYDRAULIC MONITORING OF THE SOIL SUBSURFACE

Fibre optic distributed temperature sensing (DTS) is increasingly used in environmental monitoring and for subsurface characterisation. When combined with active heating of metal elements embedded within the optical fibre cable, the temperature response of the soil to heating provides valuable information from which soil parameters, such as thermal conductivity and soil moisture content can be inferred at high spatial and temporal resolution, and over long distances.

In this manuscript, we present a novel Actively Heated Fibre Optics (AHFO) system and its application to characterise spatial and temporal dynamics in soil thermal conductivity along a recently forested hillslope in Central England, UK. The AHFO system produced comparable results to conventional measurement techniques, but at higher spatial and temporal resolutions. The larger number of measurement points provided by AHFO and the ability to repeat surveys under different meteorological/hydrological conditions allows for a more detailed examination of the spatial and temporal variability of thermal conductivities at the study site. This can improve estimates of bulk thermal conductivities and its temporal variability due to changing soil moisture conditions, and provide a better understanding of the influence of groundwater flow on heat transport processes for various applications, including ground source heat pump systems.