Rock Fraction Effects on the Surface Soil Moisture Estimates From L-Band Radiometric Measurements

The SMOS REFLEX 2006 field experiment aimed to measure vines emission during their phenological cycle and to study the impact of vegetation and rocks on the emission. Rocks were kept in half the vineyard (from 40% to 80% of surface rock fraction) and were partially removed in the other half (from 6% to 30% of surface rock fraction). Since rocks have a low and constant dielectric permittivity, their presence masks the soil dielectric increase due to soil moisture. This leads to an almost constant relationship between the measured emission and ground-truth soil moisture and, thus, to a subestimation of the soil moisture by the retrieval algorithms: i.e. the soil appears drier to the radiometer than it actually is.