L-band measurements of boreal soil

The successful launch of the European Space Agency's (ESA) Soil Moisture and Ocean Salinity (SMOS) satellite mission on November 2nd 2009 opened a new era of global monitoring with L-band passive microwave instruments. The main objective of the mission is to measure soil moisture and sea surface salinity globally. The sole payload of SMOS is the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS). In this paper we compare the first SMOS measurements over a sub-Arctic boreal forest area with tower-based and airborne reference data. Our main interest is the evolution of the boreal soil frost, since it has a large impact on the carbon cycle in the Arctic region.