The soil heat flux sensor functioning checks, imbalances' origins, and forgotten energies

Abstract

Soil heat flux is an important component of the surface energy balance (SEB) equation. Measuring it requires an indirect measurement. Every used technique may present some possible errors tied with the utilized specific technique, soil inhomogeneities, or physical phenomena such as latent heat conversion beneath the plates, especially in desiccation cracking soil or vertisol. The installation place may also induce imbalances. Finally, some errors resulting from the physical sensor presence, vegetation presence, or soil inhomogeneities may occur and are not avoidable. For all these reasons it is important to check the validity of the measurements. A quick and easy way is to integrate results over 1 year. By consideration of the inert core internal energy conservation law, it is shown that the corresponding integration should be close to zero after a necessary geothermal heat efflux subtraction. However, below-plate evaporation and vegetation-absorbed water or rainwater infiltration may also contribute to the observed short-scale and/or long-scale imbalance generating convective heat fluxes not sensed by the heat flux sensors. Another energy source is usually not included in the SEB equation: rainfall or irrigation. Yet its importance for short- and long-term integration is notable. As an example, the most used sensor, soil heat flux plates (SHFPs), is given.