Soil‐heat Flux Determination: Temperature Gradient Method with Computed Thermal Conductivities

Abstract

AbstractSurface soil‐heat fluxes were determined for 6 days in a field of Avondale loam using the null‐alignment method, the combination method, and four variations of the temperature gradient method with thermal conductivities computed from the DeVries' theory for particular reference depths. For all methods, calorimetry was used to obtain the surface flux from the flux determined for the reference depth.There was 10% or less difference between the null‐alignment, combination, and temperature gradient methods for a 20‐cm reference depth. However, the difference with respect to the null‐alignment method increased to 35% for a 5‐cm reference depth when DeVries' theory was closely followed. This difference was reduced to 3% when a modified air shape factor was used in the computations and all vapor movement was ignored. We concluded that the temperature gradient method with conductivities computed from DeVries' theory could be reliably used with a 20‐cm reference depth, but that a “calibration” of the theory for a particular soil should be obtained before the method is used with a 5‐cm reference depth.When properly used, the temperature gradient method with computed conductivities has the advantage that reliable estimates of surface soil‐heat flux can be obtained without requiring heat flux plates like the usual combination method nor many computations like the null‐alignment method.