Natural thermal emission in the 8-12 μm band as well as emission or diffusion of microwaves at low frequencies are known to be strongly correlated with the soil surface water content. Theoretical studies of the interaction between the soil/plant system and the atmosphere have shown that such measurements may be used to monitor the soil water budget. Experimental results from an airborne campaign are presented here. The surface temperature and radar cross-section spatial properties and their interrelations are examined for very different situations (wet and dry, bare and vegetated). It is shown that, as far as large-scale applications are concerned, the field scale can be considered as homogeneous for both measurements and that it is possible to derive meaningful regional information from measurements at that scale. Therefore, at least for the test region, a high spatial resolution (of microwaves and thermal infrared measurements) is not required for the monitoring of surface soil moisture and thermal equilibrium for this 10-day period.