Modeling of the L-Band emission and scattering of soil layers with consideration of Moisture and Temperature gradients.

In the context of the European Space Agency's (ESA) Soil Moisture and Ocean Salinity (SMOS) mission, we present a study of the emission and of the bistatic scattering coefficient of rough surfaces at 1.4 GHz and the effects of moisture and temperature gradients. A new approach for the calculation of rough surface scattering and emission at L-band has recently been. This approach relies on the use of ANSYS's numerical computation software HFSS (High Frequency Structure Simulator), which in turn solves Maxwell's equations using the Finite Element Method (FEM). The interest of this approach is that it can be extended to calculate the emission and scattering of complicated multilayer media, including features such as volume effects, gradients effects and inclusions, as well as rough surfaces. At L band, volume effects in the upper layer of soil should be taken into account. In particular, moisture or thermal phenomena lead to the presence of gradients. In this paper we present the work we have done to use FEM method to compute thermal effects and water infiltration effects in ground. Coupling electromagnetic and thermal computation we are able to study scattering of media such as permafrost or effects of rapid changes in temperature condition. We can also study the effect of moisture gradients or the impact of rainfall events on bistatic scattering coefficient or emissivity of soil. It can also be very useful for global observations with a frequent repeat coverage (future NASA Soil Moisture Active/Passive mission SMAP). In the present study we present the effects of water infiltration in ground (as moisture gradients) on the emissivity and bi-static scattering coefficient of soil.