Quantification of subsurface thermal regimes beneath evaporating porous surfaces

The spatial distribution and dynamics of non-uniform evaporative mass fluxes from porous media are quantified remotely from induced surface thermal field obtained by spatially resolved infrared thermometry. Conversion of surface thermal signatures to the estimation of evaporation fluxes hinges on knowledge of the unobservable characteristic thermal decay depth. We considered quasi-static evaporation fluxes combined with measured surface thermal fields within a surface energy balance model to obtain a general analytical approximation for the thermal decay depth. This approximation was experimentally evaluated using side view IR imagery of temperature fields beneath an evaporative surface. The analytical approximation reveals dependency of thermal decay depth on the magnitude of evaporative flux which was also sensitive to convection and radiation intensity. Results indicate that typical values of evapo-thermal decay depth for a wide range of natural soil surfaces is in the range of a few centimeters (<5 cm). The solution enables remote estimation of non-uniform evaporative fluxes from surface temperature fields .