Estimating Soil Surface Temperatures From Profile Temperature and Flux Measurements

This paper presents a physically based model for temperature and heat flux profiles in a homogeneous soil. It was designed to predict soil surface temperatures, which cannot usually be measured easily, from subsurface data. This is important for surface energy balance studies, including estimating evaporation. A simple but realistic surface soil heat flux model was used to calculate analytical expressions for all the coefficients and phases in the well-known Fourier series solution to the soil heat flow equations. The model depends on only four or five (depending on the application) physically realistic parameters, which may be estimated by fitting to subsurface soil temperatures or to both temperatures and fluxes. The model was tested on two bare soils and one vegetated soil. Surface temperature data were not available for comparison, but the predicted near-surface temperatures (1 cm for the bare soils and 4 cm for the vegetated soil) were accurate to about 1°C, when the soil could be considered homogeneous, and to 2 to 4°C, when variability in the thermal properties over depth and time severely violated this assumption.