Abstract
Sea Surface Salinity (SSS) is an increasingly-used Essential Ocean and
Climate Variable. The SMOS, Aquarius, and SMAP satellite missions all
provide SSS measurements, with very different instrumental features
leading to specific measurement characteristics. The Climate Change
Initiative Salinity project (CCI+SSS) aims to produce a SSS Climate Data
Record (CDR) that addresses well-established user needs based on those
satellite measurements. To generate a homogeneous CDR, instrumental
differences are carefully adjusted based on in-depth analysis of the
measurements themselves, together with some limited use of independent
reference data. An optimal interpolation in the time domain without
temporal relaxation to reference data or spatial smoothing is applied.
This allows preserving the original datasets variability. SSS CCI fields
are well-suited for monitoring weekly to interannual signals, at spatial
scales ranging from 50 km to the basin scale. They display large
year-to-year seasonal variations over the 2010-2019 decade, sometimes by
more than +/-0.4 over large regions. The robust standard deviation of
the monthly CCI SSS minus in situ Argo salinities is 0.15 globally,
while it is at least 0.20 with individual satellite SSS fields. r2 is
0.97, similar or better than with original datasets. The correlation
with independent ship thermosalinographs SSS further highlights the CCI
dataset excellent performance, especially near land areas. During the
SMOS-Aquarius period, when the representativity uncertainties are the
largest, r2 is 0.84 with CCI while it is 0.48 with the Aquarius original
dataset. SSS CCI data are freely available and will be updated and
extended as more satellite data become available.