Estimating Soil Thermal Inertia Profiles From the Passive Equilibration of a Temperature Probe
Abstract Knowledge of the distribution of soil thermal properties is important for understanding subsurface hydrological and biogeochemical processes. This study describes and evaluates quick thermal profiling (QTP), a new measurement technique aimed at providing rapid, depth‐resolved measurements of soil thermal inertia at numerous locations across the landscape. A cylindrical probe with temperature sensors at multiple depths is quickly inserted into the ground, and soil thermal inertia is estimated from how quickly the probe temperature equilibrates with the soil. To this end, a finite volume heat transfer model is used to generate temperature equilibration time series across combinations of controlling factors, and a gridded search inversion approach is applied to infer soil thermal inertia. Field tests in the Arctic indicate that QTP measurements have a minimum uncertainty of 0.14 J m −2 K −1 s −1/2 and covary with dual‐probe heat pulse thermal analyzer measurements (concordance correlation coefficient = 0.56) with a root‐mean‐square error of 0.40 J m −2 K −1 s −1/2 . Besides demonstrating the value of QTP for estimating thermal inertia, this study identifies various sources of measurement uncertainty, particularly probe‐soil contact resistance and frictional heating. Further, analysis of soil samples indicates that thermal inertia can be used to estimate thermal conductivity and dry bulk density in the studied area, although such inferences are highly site‐specific. Overall, the QTP method holds promise to generate thermal inertia data products and to complement other characterization approaches for advancing understanding of soil properties across far more locations than is currently possible. Plain Language Summary Physical properties of soil mediate the temperature of the subsurface and how it changes over time, which in turn influences the biological, geophysical, and chemical processes of soil. The important task of characterizing soil properties in the field is challenging because it usually requires digging and measuring at many locations. Here, we develop and evaluate a new, easier method to quickly measure soil thermal properties at multiple depths without digging a pit. We use a stainless steel temperature probe with sensors every five cm and insert it quickly into the ground. The thermal inertia of soil is estimated based on how quickly the temperature of the probe equilibrates with the soil. This is achieved using a computer model of heat transfer to identify soil properties that could explain the observed temperature readings. Using this method also helps to understand the distribution of other soil properties, like thermal conductivity and bulk density. Overall, the described method shows distinct advantages and limitations in various settings and potential for future development. Key Points Thermal inertia is estimated from the passive thermal equilibration of a cylindrical probe after it is inserted in the ground A metal probe houses temperature sensors at 16 depths down to 75 cm, producing a depth‐resolved profile of measurements Thermal inertia measurements at multiple depths can offer valuable insight into other soil physical properties
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- US Department of Energy; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23), Climate and Environmental Sciences Division (SC-23.1 )
- Grant/Contract Number:
- AC02-05CH11231
- OSTI ID:
- 3013085
- Journal Information:
- Journal of Geophysical Research (JGR): Biogeosciences, Journal Name: Journal of Geophysical Research (JGR): Biogeosciences Journal Issue: 12 Vol. 130
- Country of Publication:
- United States
- Language:
- English
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