Estimation from Soil Temperature of Soil Thermal Diffusivity and Heat Flux in Sub-surface Layers

Abstract

Soil thermal parameters are important for calculating the surface energy balance and mass transfer. Previous studies have proposed methods to estimate thermal parameters using field data; however, the application of these methods lacks validation and comprehensive evaluation under different climatic conditions. Here, we evaluate four methods (amplitude, phase shift, conduction–convection and harmonic) to estimate thermal diffusivity (k) under different climatic conditions. Heat flux was simulated and compared with data from heat-flux plates to validate the application of the four methods. The results indicated that, under clear-sky conditions, the harmonic method had the greatest accuracy in estimating k, though it generated large errors on rainy days or under overcast conditions. The conduction–convection method (CCM) provided a reliable estimate of k on rainy days, or under overcast skies, coinciding with increased water movement in the soil profile. The amplitude method, although a simple calculation, had poor accuracy for rainy and overcast conditions. Finally, the phase shift method was shown to be a suitable alternative for CCM to estimate k under overcast conditions, though only when soil moisture content was high.