Assessment of the topography impact on microwave radiometry at L-band

The TuRTLE 2006 field experiment aimed at evaluating, from a ground-based point of view, the topography impact on microwave radiometry at L-band. Observations of a mountainous area 50 km north of Barcelona, Spain, were acquired using the fully polarimetric radiometer LAURA (1.4135 GHz working frequency). The look angle was changed in elevation and azimuth to observe a wide area which included almost bare surfaces, shrubs growing at the valley descending slope, and mixed woodland present at the ascending slope of the mountain in front of LAURA (at the other side of the valley). Ground-truth soil moisture and temperature, vegetation water content, and meteorological parameters were also sampled. Radiometric measurements have been compared to antenna temperatures simulated using a facet model which takes into account the high-resolution digital elevation model and the land cover map of the experiment site, the polarization mixing due to surface tilting, and the radiometer's antenna radiation pattern. Four different scenarios have been simulated: (1) a hypothetical scenario without vegetation and without topography, (2) a hypothetical scenario without topography but with the actual land cover map of the experiment site, (3) a hypothetical scenario without vegetation but with the digital elevation map of the experiment site, and (4) the actual experiment site, including both the digital elevation model and the land cover map. Simulations using a facet model agreed with measurements only when both topography and the land cover map were considered. The largest discrepancies occur for almost bare soils at large local incidence angles, which suggests that further modeling work is still needed for this case.