L-Band Radiometric Observations of Sun Glint Over Land Surfaces

Sun radio emission can be an important interference source for future satellite missions such as NASA/CONAE Aquarius-SAC-D, and ESA´s SMOS, which will measure soil moisture and sea surface salinity. Radiometric measurements can be interfered by Sun directly, by leakage through the antenna side lobes, or reflected on the Earth´s surface towards the antenna. Direct and reflected Sun measurements were acquired from a ground-based radiometer during the T-REX 2006 experiment. Direct observations of Sun induced an increment of 130 K on the brightness temperature, which is in accordance with theoretical estimates. However, no significant increment on the land brightness temperature due to Sun glint has been detected in measurements at the range of incidence angles from 90deg to 60deg respect to nadir, which seems to indicate that scattered Sun may not be a problem in SMOS, where scattering angles are larger than 45deg, and typically around 65deg.