Soil Moisture Retrievals Over Partially Forested Areas in Aurajoki Catchment, Western Finland

Coarse ground resolution limits the accuracy of current passive L-band satellite missions for soil moisture retrieval such as soil moisture and ocean salinity and soil moisture active and passive, as many of their pixels contain different land cover types. One of the significant uncertainty factors is introduced by dense vegetation, especially in areas where land cover varies between forest and open areas, which is often the case in inhabited areas in the Boreal zone. In this paper, we study the soil moisture retrieval with the help of fine resolution L-band airborne radiometer in case of heterogeneous pixels in the boreal forest region, and attempt to quantify and isolate the influence of the different terrain types. The work is based on a series of airborne radiometer measurements with the HUT-2D interferometric radiometer in Finland. Radiometer-derived soil moisture values are compared with soil moisture estimates given by watershed simulation and forecasting system model, which is validated and refined by using in-situ measurements so that its accuracy is augmented. Our results suggest that it is possible to retrieve soil moisture in agricultural areas in a heterogeneous pixel with substantial (30 %) forest cover achieving accuracy of 0.032 m³/m³ and that L-band radiometry may be useful in research of hydrological processes in wetlands.