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measurements undersampling and/or smoothing by the OI applied to the ISAS. In
addition, the SMOS freshening could be linked to the different depth of the mea-
surements (SMOS at 1 cm and in situ SSS measured at several meters depths) as
described in Sects.
4.1
and
4.2
.
Finally, to illustrate the potential impact of the vertical stratification effect on the DSSS
differences between satellite and in situ, we compare along the drifter trajectory the salinity
measured at 45-cm depth by a surface float (Reverdin et al.
2012
) in the 2010 rainy western
Pacific with monthly SSS maps (Fig.
23
). The drifter SSS data clearly indicate a large
signature of rainy events, with typical freshening events 1 pss for more than 1 day. The
ISAS SSS is on the upper range of the drifter SSS, while monthly SMOS SSS is sys-
tematically on the lower range in this rainy region. While more work is certainly needed to
determine the physical sources for these observed differences, the vertical SSS stratifica-
tion associated with rain events, as illustrated by this case, is a likely contributor to the
different signatures in the interannual SSS variability as detected by the SMOS satellite
SSS data and the Argo data.
These preliminary results confirms the capability of L-band radiometry in detecting
large SSS signals and their low-frequency variability (here over a 2-year period), in spite of
much noisier satellite than in situ measurements. In general, this results from much better
satellite-based temporal coverage and with a better spatial resolution, thus offering com-
plementary information to existing in situ measurements.
Fig. 23 Top: trajectory of a surface velocity program (SVP) float in the western Pacific region measuring
conductivity and temperature at 45-cm depth. Bottom: SSS along the drifter trajectory measured by the
drifter (green), derived from SMOS monthly map (blue), from ISAS monthly map (red)
