SMOS Instrument Performance and Calibration After 6 Years in Orbit

Abstract:

ESA’s Soil Moisture and Ocean Salinity (SMOS) mission has been in orbit for over 6 years, and its Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) in two dimensions keeps working well. The data for this whole period has been recently reprocessed with the new fully polarimetric version (v620) of the Level-1 processor which also includes refined calibration schema for the antenna losses. This reprocessing has allowed the assessment of an improved performance benchmark.

The long term drift exhibited by the previous processor version has been significantly mitigated thanks to a better calibration of the antenna losses and the use of only the most accurate Noise Injection Radiometer. These improvements have also reduced the orbital and seasonal variations, although residual drifts still remain, in particular during the satellite eclipse season. The spatial tilt existing in the images produced with the previous version of the Level-1 processor has been considerably decreased, removing the negative trend at low incidence angles and reducing the overall standard deviation of the spatial ripples. The expected improvement in the 3rd and 4th Stokes, after correcting the use of the cross-polar antenna patterns, has been confirmed, enabling accurate retrieval of the Faraday rotation angle. Finally, a better Sun and RFI flagging strategy has been implemented, allowing for the removal of the corrupted data. A problem which still persist in the new Level-1 data is the land-sea contamination. However, recent progress in the calibration investigations has shed new light on the origin of the land-sea contamination, linking it to visibility amplitude calibration errors. Thus, future versions of the Level-1 processor will have very much reduced land-sea contamination.

An overview of the results and the progress achieved in both calibration and image reconstruction will be presented in this contribution.