Validation of SMOS soil moisture retrievals in Aurajoki catchment, Western Finland

European Space Agency´s SMOS mission delivers global maps of soil moisture, an important parameter in research of the Earths hydrosphere. The relatively coarse surface resolution of SMOS causes the pixels to cover several different types of soil and vegetation, and in order to reliably retrieve soil moisture it is vital to know the properties of all the emitters. Boreal zone is a challenging area for remote measurements of soil moisture, since it is largely covered by different types of vegetation and exhibits a large temporal and spatial variation in surface conditions. This paper examines the reliability of SMOS measurements over a test area in Finland by comparing the SMOS brightness temperatures to airborne radiometer measurements as well as SMOS soil moisture retrievals to values from a watershed model and in situ measurements. Findings of this paper suggest, that the retrieval results could be improved through better consideration of the properties of different soil types.