Passive microwaves at L-band (1.4 GHz) can be used to estimate near surface soil moisture from satellites at a global scale. Soil moisture affects very strongly surface dielectric properties at this frequency and thus surface brightness temperature. Current studies are focused on the improvement of surface emissivity models for specific conditions regarding surface roughness, type of vegetation cover and geometry of observation. The airborne-based campaign EuroSTARRS from the European Space Agency will provide experimental data to support the development and improvement of these models. The basis of microwaves for surface soil moisture estimation is presented in this communication, together with some preliminary results of the EuroSTARRS-2001 campaign.