The Soil Moisture and Ocean Salinity mission (SMOS) is the European Space Agency (ESA) second Earth Explorer. It was launched on 2nd November 2009, and it continues to provide L-band Brightness Temperature (BT) measurements from which a number of applications are derived. More notoriously, soil moisture measurements, sea surface salinity, sea-ice thickness and high wind speeds. Its payload, the Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) continues to be the first and only 2D radiometer interferometer ever flown to space for Earth Observation. 12 years after launch, SMOS is still in good health, and the SMOS calibration team continues to further improve the quality of the data. Most recently, the 3rd Mission Reprocessing level 1 data set was released, after a number of improvements performed in calibration and the image reconstruction process. Among the changes introduced in calibration for the 3rd Mission Reprocessing release, there was the change in strategy for the Noise Injection Radiometer calibration, that became fixed after the team realised that this particular receiver is far more stable than what can be measured in calibration; the update of the Power Measurement System (PMS) thermal sensitivity and NIR antenna losses characterization values, and the introduction of a thermal latency parameter for the thermal sensor in the NIR antenna. Among the changes in the image reconstruction process, the most relevant were the refinement of the Gibbs correction (called Gibbs-2) to account for differences in the Sea and Land BT, the introduction of the super-sampled Sun BT correction, to account for inhomogeneities of the L-band Sun BT signal within the Sun disk, the correction of the Sun BT signal even when the Sun is in the back of the instrument, which is observed through the side-lobes, and the addition of new Radio Frequency Interference (RFI) flags to alert users of a degradation of certain BT measurements. All these changes introduced a clear positive jump in the quality of the level 1 SMOS data, as assessed by the different metrics that the SMOS team uses to assess it. The most important changes were a clear improvement in the stability of the data and a reduction on the spatial biases observed. The improvement in the different metrics will be presented at the conference. Currently, the team still continues to improve the data in view of a 4th Mission Reprocessing. Some of the most important new changes that the team is working on are the introduction of a RFI correction, to remove RFI signal from the BT measurements, a new antenna thermal model, to account for variations of the antenna losses parameters as function of the antenna temperature, further refinements of certain calibration parameters, to reduce Land-Sea contamination and some residual orbital instability drift in certain times of the year where the variation of physical temperature is larger. Finally, the team is also working in developing new level 1 products: the SMOS solar flux, which can be provided in near-real time and could be extremely useful for the detection of Solar flares, and a new Total Electron Content (TEC) product derived from SMOS measurements. A summary of all these changes, improvements and metrics will be presented during the conference

Living Planet Symposium, 23-27 May 2022, Bonn, Germany

Peer reviewed