Jack R Lamb

and 7 more

Knowledge of soil thermal conductivity is critical for understanding geophysical and biogeochemical processes in the subsurface. This study describes and evaluates a new measurement technique that provides rapid, depth-resolved measurements of soil thermal conductivity without digging a soil pit. Quick thermal profiling (QTP) interprets the passive thermal equilibration of a temperature probe after it is inserted in soil. Temperature is recorded simultaneously at 5-centimeter depth intervals down to 75 centimeters, providing vertically resolved data. Soil thermal properties are probabilistically estimated using a finite volume model simulating heat transfer and a gridded search inversion method. The use of prior soil properties measurements to constrain the inversion is also assessed. Field tests on the Seward Peninsula (Alaska, USA) indicate that the QTP estimates of thermal conductivity correlate significantly with in-situ measurements using a thermal properties analyzer (R2 = 0.56, n = 22). In addition, the vertical change in thermal conductivity enables estimates of peat layer thickness that correlate with visual observation from soil pits (R2 = 0.76, n = 10). QTP tends to underestimate thermal conductivity compared against a thermal analyzer (slope = 0.633), though estimates in peat soil layers are more accurate than those in a deeper silty mineral soil layer. The uncertainty of QTP conductivity estimates is found to arise from non-uniqueness in the solution space, as well as from discrepancies between field conditions and the heat transfer model. Overall, QTP presents a promising pathway for the future development of quick, depth-resolved soil thermal conductivity measurement techniques.