Soil Moisture and Ocean Salinity (SMOS) is the second Earth Explorer Opportunity mission developed as part of the European Space Agency (ESA) Living Planet programme. SMOS ws launched on 02 November 2009. The SMOS mission provides two-dimensional interferometric radiometer measurements of L-band (1.4 GHz) brightness temperature from a satellite in polar orbit. At this frequency the atmosphere is almost transparent and surface emission is strongly related to soil moisture over continental surfaces and salinity over oceans.

The key objectives of the SMOS mission are to:

• Improve our understanding of the global water cycle.
• Contribute to the improvement in weather and seasonal-climate forecasting.

ECMWF plays a major role in developing and implementing the use of SMOS brightness temperature data in NWP models. ECMWF’s contribution to the SMOS mission is two-fold:

• Development of a data monitoring system for the SMOS near real time product to provide a timely quality check for ESA and the SMOS calibration and validation teams.
• Assimilation of SMOS brightness temperature data in ECMWF's global NWP system through the Surface Data Assimilation System (SDAS) based on the Extended Kalman Filter. This system is currently being tested with the active microwave METOP/ASCAT surface soil moisture data

One main component of the monitoring is the observation operator that transforms model fields (soil moisture and ocean salinity) into observation equivalent (brightness temperatures).

To this end the CMEM (Community Microwave Emission Modelling Platform) has been developed at ECMWF.

ECMWF ESA Reports on SMOS:

• Rodriguez-Fernandez N.J., P. de Rosnay, C. Albergel, F. Aires, C. Prigent, P. Richaume, Y.H. Kerr, J. Muñoz-Sabater: "SMOS Neural Network Soil Moisture Data Assimilation". January 2017 (pdf)

• Muñoz-Sabater, J., N.J. Rodriguez-Fernandez, P. Richaume, C. Albergel, P. de Rosnay, Y.H. Kerr: TR2-WP4020-part 2: "SMOS Near-Real-Time Soil Moisture processor: Operational chain and evaluation". January 2016 (pdf not available yet)

• Muñoz Sabater, J., P. de Rosnay, C. Albergel, L. Isaksen: Phase II, WP3401 & 3402: "SMOS report on model background and observation error scenarios". January 2016 (pdf)

• Rodriguez-Fernandez, N., P. Richaume, J. Muñoz-Sabater, P. de Rosnay, Y.H. Kerr, TR2-WP4020-part 1: " SMOS Near-Real-Time Soil Moisture processor. Part 1: Neural network evaluation and algorithm description". Dec. 2015 (pdf)

• Muñoz Sabater J., P. de Rosnay, C. Albergel, L. Isaksen: Phase II, WP2000 & WP2100: "SMOS report on level-3 root zone soil moisture and data assimilation impact". February 2014 (pdf).
• Muñoz Sabater J., M. Dahoui, P. de Rosnay, L. Isaksen: Phase II, WP1100: "SMOS Monitoring Report number IV". January 2014 (pdf)
• Muñoz Sabater J., P. de Rosnay, L. Isaksen, Phase II, WP2300: "Hot-spot analysis". December 2013 (pdf)
• Muñoz Sabater J., P. de Rosnay, A.Fouilloux, M. Dahoui, L. Isaksen, C. Albergel, I. Mallas, T. Wilhelmssom: Tech. Note, Phase I: "Final Report". January 2013 (pdf)
• Muñoz Sabater J., M. Dahoui, P. de Rosnay, L. Isaksen: Technical Note, Phase II, WP1100: "SMOS Monitoring Report number III: Dec-2011 - Dec-2012". April 2013 (pdf)
  
• Muñoz Sabater J., M. Dahoui, P. de Rosnay, L. Isaksen: Technical Note, Phase II, WP1100: "SMOS Monitoring Report number II: Nov-2010 - Nov 2011". Dec. 2011 (pdf)
• Muñoz Sabater J. and P. de Rosnay "SMOS report on noise filtering", Technical Note - Phase-II - WP1300 ESA/ESRIN Contract, November 2011, (pdf)
• Muñoz Sabater J., P.de Rosnay, M. Dahoui: "SMOS continuous monitoring report - Part 1; February 2011" (pdf)
• Muñoz Sabater J., T. Wilhelmsson, P. de Rosnay and L. Isaksen "SMOS Report on data thinning" - Technical Note - Phase II - WP1200; August 2011 (pdf)
• Muñoz Sabater J., P.de Rosnay, A.Fouilloux: Milestone 2 Tech Note - Parts 1/2/3: "Operational Pre-processing chain, Collocation software development and Offline monitoring suite"; December 2010 (pdf)
• de Rosnay, P., M. Drusch and J. Muñoz Sabater: Milestone 1 Tech Note - Part 1: "SMOS Global Surface Emission Model" November 2009 (pdf)
• Muñoz Sabater J., P.de Rosnay, A.Fouilloux, M. Dragosavac and A.Hofstadler: Milestone 1 Tech Note - Part 2: "IFS Interface" November 2009 (pdf)

ECMWF peer-reviewed articles on SMOS:

• J. Muñoz-Sabater, 2015: “Incorporation of microwave passive brightness temperatures in the ECMWF soil moisture analysis”. Remote Sensing. 7(5), 5758-5784; doi:10.3390/rs70505758.
• J. Muñoz-Sabater, P. de Rosnay, C. Jimenez, L. Isaksen and C. Albergel. 2014: “SMOS brightness temperatures angular noise: characterization, filtering and validation”. IEEE Trans. on Geosci. and Remote Sens., 52, (9), 5827-5839, doi:10.1109/TGRS.2013.2293200.
• J. Muñoz Sabater, Fouilloux. A. and de Rosnay, P., 2012: “Technical Implementation of SMOS Data in the ECMWF Integrated Forecasting System”, IEEE Geosc. and Remote Sens. Letters, 9(2), 252-256. doi:10.1109/LGRS.2011.2164777.
• J. Muñoz Sabater, de Rosnay, P., and Balsamo, G., 2011: "Sensitivity of L-band NWP forward modelling to soil roughness”, Int. Journal of Remote Sens., 32 (19),5607-5620. doi:10.1080/01431161.2010.507260.
• de Rosnay P., M. Drusch, A. Boone, G. Balsamo, B. Decharme, P. Harris, Y. Kerr, T. Pellarin, J. Polcher and J.-P. Wigneron, "The AMMA Land Surface Model Intercomparison Experiment coupled to the Community Microwave Emission Model: ALMIP-MEM", J. Geophys. Res., Vol 114, 2009, doi: 10.1029/2008JD010724
• Drusch, M., T. Holmes, P. de Rosnay and G. Balsamo, 2009: Comparing ERA-40 based L-band brightness temperatures with Skylab observations: A calibration / validation study using the Community Microwave Emission Model, Vol 10, DOI: 10.1175/2008JHM964.1, J. Hydromet.