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Emissivity and backscattering have different sensitivities to soil and vegetation parameters and provide complementary information on the observed scene. For this reason, the main objective of this study was to investigate the potential of the combined use of active and passive microwave signatures to improve the understanding of emission and scattering mechanisms over land. The discrete scattering model developed by the Tor Vergata University, driven by a single set of input parameters, was used to simulate both emission and backscattering. The model accuracy was assessed by comparing modelled emissivity, multiplied by the effective temperature, with C-band AQUA AMSR-E observations and modelled backscattering coefficient with Metop ASCAT observations. The investigation was carried out using datasets collected over the Maqu area, which is located in the north-eastern part of the Tibetan Plateau and is covered by homogeneous grassland with a thin litter layer. In situ soil moisture measurements and MODIS Terra/Aqua 8-days LAI products served as model inputs, whereas the most sensitive other parameters, such as surface roughness and litter and vegetation parameters, were calibrated to obtain the best match between modelled outputs and both ASCAT and AMSR-E 2009 observations. With the calibrated parameters, measured soil moisture and MODIS LAI as input, the model correctly simulated the temporal variations of ASCAT backscattering coefficient, with R2 of 0.9 and rmse of 0.5 dB. The results obtained in the passive case strongly depended on the adopted effective temperature. The best match with satellite observations was found when the surface temperature was obtained from Ka-band AMSR-E data, leading to R2 of 0.8 and rmse of 6 K for H polarisation data and R2 of 0.5 and rmse of 6 K for V polarisation data. The validation carried out using the 2010 data, without any further refinement of the calibrated parameters, showed a slightly worse agreement between modelled and observed signatures. The results showed that the combined use of active and passive microwave signatures contributed to an unambiguous interpretation of emission and scattering processes over the study area, it allowed us to impose constraints to non-available inputs of the Tor Vergata model and it led to correct simulations of the satellite signatures. These findings are important to better understand the potential of the synergistic use of radiometer and radar data, like those to be provided by NASA's SMAP.

International audience; From July-December 2004 the experimental campaign 'Bray 2004' was conducted in the coniferous forest of Les Landes near Bordeaux, France, using a multi-angle L-band (1.4 GHz) radiometer to measure from above the forest at horizontal polarization. At the same time, ground measurements were taken of soil and litter moisture content, while precipitation was also permanently monitored. This experiment was done in the context of the upcoming SMOS mission in order to improve our understanding of the behaviour of the L-band signal from forested areas for different wetness conditions and viewing angles. This is especially relevant for solving the problem of heterogeneity since a large fraction of SMOS pixels (similar to 30 x 30 km 2) is partially covered by forest. This paper describes the objectives and the overall set-up of the Bray-2004 experiment and shows some first results. The greater part of the horizontally polarized L-band signal is found to be dominated by the influence of physical temperature. Variations in soil and/or litter moisture content are visible in the angular signal and in the above-canopy microwave emission, although the dynamic range of this last effect is very small. This, together with the fact that emissivity values are very high, is possibly due to the presence of a substantial litter layer. However, decoupling of soil and litter effects is difficult because of the strong correlation found between soil and litter moisture. (C) 2006 Elsevier Inc. All rights reserved.