DiHPS - A Distributed Heat Pulse Sensor Network for the quantification of subsurface heat and water fluxes

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We propose the development of a novel, distributed soil moisture and temperature monitoring network that will present a step change from currently available monitoring technologies, which tend to be based on data collection at isolated points in time and space, to real-time, spatially-distributed data collection that enable effective and responsive decision making to deal with rapidly increasing demands in a changing climate.The proposed system will be based on combining Distributed Temperature Sensor (DTS) technology with an active heat source. The so-called Active DTS (A-DTS) allows observing flow-related heating and cooling patterns along the actively heated cable. It is this Distributed Heat Pulse, A-DTS technology that we will use in the development of the proposed Sensor network - DiHPS. While broader applications in heat and water flux assessments will be possible with DiHPS, in this project we will focus on demonstrating its suitability to quantify the moisture content and thermal properties of the soil.Description of the spatial and temporal distribution/ dynamics of these soil parameters is important for many agricultural, engineering and meteorological applications. Soil moisture, for example, is a key state variable in controlling land-atmosphere interactions and an early indicator of changes in the hydrological system, e.g. associated with daily evapotranspiration or event-based recharge cycles or with extreme events (i.e., droughts or floods). It is widely used in agriculture (e.g., irrigation management), forestry (e.g. plantation water demand estimations), meteorology (e.g. local and regional weather forecasts), water resources management (e.g. estimation of groundwater recharge) as well as a state indicator variable in drought / flood early warning systems. Soil thermal properties influence the partitioning of energy within the ground and at the ground surface, and are related to soil temperature and the movement of heat and water within the ground and their transfer across the ground surface. For these reasons, soil physicists, crop scientists and micrometeorologists study thermal properties, and they are also important in engineering applications, (e.g., determining the electric current rating of buried cables, ground heat exchanger design). We will build on earlier work which has demonstrated the principal capacity of A-DTS to measure soil moisture under controlled conditions in a lysimeter facility. We will expand this technology from a single point application to a distributed, real time sensor network and a coiled, vertical A-DTS profiler for measuring soil moisture content and thermal properties at high spatial and temporal resolution. The network and profiler will be tested at TRL4 by installing it at our test site at the Birmingham Institute for Forestry Research (BIFoR). The results will be compared with in-situ soil moisture content and thermal property data from Frequency-Domain Reflectometry (FDR) soil moisture probes and thermal needle probe measurements, respectively. To achieve real-time, autonomous system operation, a set of heating strategies will be tested and initial threshold (trigger values) will be defined. These will define at what change in soil temperature, as observed by continuous temperature observation in DTS passive mode, initiation/cessation of the DTS active mode will be triggered. A key component of DiHPS is the real-time control for triggering the change from active to passive observation mode. This will require the development of a set of algorithms, based on inverse modelling and asymptotic approaches, which can process the raw DTS data in real-time to provide the required outputs. No existing DTS-application attempts to provide temperature or soil moisture data temperature in such detail and in real-time. If successful, we anticipate a step change in the way DTS is employed, e.g. in early warning systems or for providing detailed process understanding.