Ground Surface‐Soil Thermal Inversion From In Situ Measurement

Abstract

Soil heat flux at the ground surface (G) is an essential component of energy for the recirculation of water and other masses on the land surface. However, direct measurement is difficult and inaccurate, and available data are inadequate owing to the inconvenience of installing the heat sensor plate immediately beneath the true surface. Additionally, thermal properties such as the diffusivity, conductivity, and volumetric heat capacity are intricately influenced by water, vegetation, labile weather, and environmental conditions. Errors of estimation for them from indirect measurement of water content can be substantial and almost impossible without adequately and accurately determination of the soil parameters in situ. In this study, a more general parabolic heat equation is analytically solved for thermal diffusion of gradually varying state properties, and an inverse method is used to determine the parameters so that the properties and G can be simultaneously obtained at a site of measurement. Comparison and validation against data from a numerical model and experimental‐site measurements indicate well agreement and consistency. The retrieved G reveals relatively larger in scale that indicates a non‐negligible disparity from the under‐surface plate measured and the estimations by previous heat‐correction methods, suggesting that G should be regarded more significant in roles for the studies of near‐surface processes, particularly in rather dry conditions and in sub‐diurnal time scale. The present inversion provides some insights into the soil thermal physics of the land surface. Finally, a formula is suggested for the completion of the plate‐based heat flux measurements.