Presented at the 2015 International Geoscience and Remote Sensing SymposiumA novel downscaling methodology for intermediate spatial resolution radiometer data is developed in view of forthcoming SMAP mission. It is based on an active and a passive microwave forward model coupled by its ancillary parameters. The combined active/passive model introduced in this work yields backscatter and emission observations relation consistent with Aquarius/SAC-D observations and with what it has been reported in previous papers. Furthermore, merging spatial resolution between radar-derived and radiometer-based brightness temperature (Tb) is performed in a least-square framework. Methodology is tested using a synthetic numerical simulation example which showed that this approach leads to an increase of downscaled Tb accuracy.