This project is to be undertaken in the framework of the SMOS mission, an Earth Explorer Opportunity mission (Living Planet Programme by the European Space Agency). Since its launch in 2009, its unique payload, the MIRAS (Microwave Imaging Radiometer by Aperture Synthesis) has produced a continuous stream of calibrated radiometric data to develop high level Ocean Salinity and Soil Moisture products. Now the mission is in operations phase and the MIRAS radiometer measuring in full polarisation mode, provides soil moisture and ocean salinity information regularly to the SMOS Validation and Retrieval team and to the entire research community. Thanks to the excellent technical status and the scientific results achieved, the mission has been extended by ESA to 2019 and beyond, pending a successful review of its performance in 2018, to the end of ESAs 5th Earth Observation Envelope Programme. The current proposal builds on the successful activities performed so far by the research team in the frame of the SMOS project and it is aimed to address the mission current hot points. These can be summarized into two main general objectives: brightness temperature spatial bias reduction and orbital and seasonal drift minimization. Two additional complementary objectives that have the potential of technology transfer to the industry are also addressed: the study of SMOS new array configurations (low side lobe level) for future missions and the up-grade of UPC SMOS data processor (MIRAS Testing Software). This general objectives particularize to the following tasks: 1. SMOS enhanced full-pol radiometric performance The main topic currently addressed regarding spatial bias is the mitigation of the Land Sea Contamination (LSC) by means of a Gibbs 2 image reconstruction technique, that reduces the floor error, and different techniques to assure that amplitude errors in the set of visibility samples are consistent. A close interaction with the scientists is required to decouple residual instrumental errors from the errors caused from mismodeling of the different contributions used to set the geophysical model. 2. Impact of antenna errors and array distortion on SMOS full-pol spatial bias Preliminary results show that antenna pattern phase errors seem to be the main contributor to the LSC artifact. If the underlying assumption is confirmed, is of outmost importance for the industry related to the design of the array for a SMOS follow-on mission. 3. SMOS enhanced stability and absolute accuracy After recent calibration and image reconstruction improvements, SMOS radiometric performance is outstanding since both long term and orbital stability are constrained within a few tenths of a Kelvin. However, there still is some margin for further improvement since performance plots reveal a systematic error behaviour. 4. SMOS follow-on preparatory activities and other missions As SMOS is getting more and more consolidated as a successful mission, several initiatives to set the path for future SMOS follow-on missions with enhanced performance have taken place. These first attempts have been mainly addressed to analyze different array configurations that can provide better spatial coverage and more robust performance. 5. MTS (MIRAS Testing Software) update MTS has been periodically updated according to the SMOS mission needs and evolution and it will follow updating during this project.