Determination of upward/downward soil water fluxes using soil thermal profile series : two field case studies

Water transfer through the unsaturated zone, in terms of upward or downward water fluxes, is a critical term for estimation of the water budget. As fluid flow modifies diffusive heat transfer through advective processes, since the early 90s several studies have attempted to deduce vertical water flow from soil temperature series. Likewise, if information on the water content profiles is known, bulk thermal properties can be inferred from thermal time series at different depths.

In this study we compare two field sites in the Paris Basin Area, with two different types of soil and vegetation. We present our preliminary results from two approaches aiming at retrieving inferring soil bulk thermal parameters, namely heat capacity and conductivity, as well as vertical water flow.

On the one hand, thermal measurements until a depth of 1.8 m have been carried out in a managed crop field. Using frequency decomposition of the thermal series, the upward and downward flows are determined. The water fluxes are compared with high-frequency EM time-lapse maps in an attempt to spatialize the variations.

On the other hand, the thermal properties of a wetland area are inferred from soil thermal time series inversion using the thermo-hydrodynamic code suite Ginette, and are compared with spatial distribution of vegetation derived from remote sensing imagery.

The two approaches are compared and discussed with their respective caveats and abilities.