Satellite-based Time-Series of Sea Surface Salinity designed for Ocean
and Climate Studies
Abstract
Sea Surface Salinity (SSS) is an Essential Ocean and Climate Variable,
which is increasingly used as part of climate studies. SSS measurements
are available from three satellite missions, SMOS, Aquarius and SMAP,
each with very different instrument features leading to specific
measurement characteristics. The Climate Change Initiative Salinity
project (CCI+SSS) aims to produce SSS Climate Data Record (CDR) to
include satellite measurements, based on well-established user needs. To
generate a homogeneous CDR, instrumental differences are carefully
controlled by analysing SSS discrepancies, then adjusted based on
in-depth analysis of the measurements themselves together with
independent reference data. However, no spatial smoothing or temporal
relaxation to reference data is applied in order to maintain the
variability contained in the original data set. SSS CCI fields are well
suited for monitoring weekly to interannual variability from the ocean
basin scale to the large mesoscale. Thus, they depict that over the
2010-2019 decade, seasonal have varied greatly from year to year,
sometimes by more than +/-0.4 over large regions. When monthly SSS CCI
are compared with in situ Argo salinities, the robust standard deviation
of their difference, at global scale, is 0.15, while
r2 is 0.97. This high level of performance highlights
the benefit of the SSS CCI merging approach compared to individual
satellite SSS fields alone. The correlation with independent ship SSS
(r2>0.9) further highlights the excellent
performance of the data set. SSS CCI data are freely available and will
be updated and extended in the future as more satellite data become
available.