Abstract
Abstract. Soil temperature has been recognized as a property that strongly influences a myriad of hydro-biogeochemical processes and reflects how various properties modulate the soil thermal flux. In spite of its importance, our ability to acquire soil temperature data with high spatial and temporal resolution and coverage is limited because of the high cost of equipment, the difficulties of deployment, and the complexities of data management. Here we propose a new strategy that we call distributed temperature profiling (DTP) for improving the characterization and monitoring near-surface thermal properties through the use of an unprecedented number of laterally and vertically distributed temperature measurements. We developed a prototype DTP system, which consists of inexpensive, low-impact, low-power, and vertically resolved temperature probes that independently and autonomously record soil temperature. The DTP system concept was tested by moving sequentially the system across the landscape to identify near-surface permafrost distribution in a discontinuous permafrost environment near Nome, Alaska, during the summertime. Results show that the DTP system enabled successful acquisition of vertically resolved profiles of summer soil temperature over the top 0.8 m at numerous locations. DTP also enabled high-resolution identification and lateral delineation of near-surface permafrost locations from surrounding zones with no permafrost or deep permafrost table locations overlain by a perennially thawed layer. The DTP strategy overcomes some of the limitations associated with – and complements the strengths of – borehole-based soil temperature sensing as well as fiber-optic distributed temperature sensing (FO-DTS) approaches. Combining DTP data with co-located topographic and vegetation maps obtained using unmanned aerial vehicle (UAV) and electrical resistivity tomography (ERT) data allowed us to identify correspondences between surface and subsurface property distribution and in particular between topography, vegetation, shallow soil properties, and near-surface permafrost. Finally, the results highlight the considerable value of the newly developed DTP strategy for investigating the significant variability in and complexity of subsurface thermal and hydrological regimes in discontinuous permafrost regions.
Highlights
Soil temperature and its spatial and temporal variability mediate a myriad of above- and below-ground hydrobiogeochemical processes
We introduce a novel sensing strategy that we call distributed temperature profiling (DTP) – a strategy for obtaining spatially and temporally dense soil temperature measurements at flexible spatial scales – and we test this strategy to investigate the permafrost distribution in a discontinuous permafrost environment
The DTP dataset shows that the lateral variability in soil temperature at the 0.8 m depth is very low over some distance intervals but very abruptly varies in several other locations, with changes of up to 6 ◦C occurring over a 5 m distance or less (Fig. 2)
Summary
Soil temperature and its spatial and temporal variability mediate a myriad of above- and below-ground hydrobiogeochemical processes. Soil temperature is an important factor influencing the water and energy exchanges with the atmosphere, including evaporation (Smits et al, 2011). Soil temperature influences many processes, but in turn it is controlled by climatic forcing and modulated by canopy characteristics, snow insulation, surface water, soil thermal. Time series of soil temperature can be used to estimate the influence of the above factors on the thermal regime. Time series of temperature measurements can be used in a parameter estimation framework to quantify the thermal parameters and, potentially, the fraction of soil constituents including organic matter content (Nicolsky et al, 2009; Tran et al, 2017). Thermal temporal variability is used to investigate fluid fluxes, surface-water–groundwater exchange, and groundwater recharge (Briggs et al, 2012; Stonestrom and Constantz, 2003)
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