Contribution of future wide-swath altimetry missions to ocean analysis and forecasting
Authors: Bonaduce Antonio , Benkiran Mounir , Remy Elisabeth , Le Traon Pierre Yves , Garric Gilles 
Published: November 2018

Abstract. The impact of forthcoming wide-swath altimetry missions on the ocean analysis
and forecasting system was investigated by means of OSSEs (observing system
simulation experiments). These experiments were performed with a regional data assimilation system,
implemented in the Iberian–Biscay–Ireland (IBI) region, at 1∕12∘
resolution using simulated observations derived from a fully eddy-resolving
free simulation at 1∕36∘ resolution over the same region. The
objective of the experiments was to assess the ability of different satellite
constellations to constrain the ocean analyses and forecasts, considering
both along-track altimeters and future wide-swath missions; consequently,
the capability of the data assimilation techniques used in the Mercator Ocean
operational system to effectively combine the different kinds of
measurements was also investigated. These assessments were carried out as part of a European Space Agency (ESA)
study on the potential role of wide-swath altimetry in future versions of the
European Union Copernicus programme. The impact of future wide-swath
altimetry data is evident for investigating the reliability of sea level values in
OSSEs. The most significant results were obtained when looking at the sensitivity
of the system to wide-swath instrumental error: considering a constellation
of three nadir and two “accurate” (small instrumental error) wide-swath
altimeters, the error in ocean analysis was reduced by up to 50 %
compared to conventional altimeters. Investigating the impact of the
repetitivity of the future measurements, the results showed that two
wide-swath missions had a major impact on sea-level forecasting – increasing
the accuracy over the entire time window of the 5-day forecasts – compared
with a single wide-swath instrument. A spectral analysis underlined that the
contributions of wide-swath altimetry data observed in ocean analyses and
forecast statistics were mainly due to the more accurate resolution,
compared with along-track data, of ocean variability at spatial scales
smaller than 100 km. Considering the ocean currents, the results confirmed
that the information provided by wide-swath measurements at the surface is
propagated down the water column and has a considerable impact (30 %) on
ocean currents (up to a depth of 300 m), compared with the present
constellation of altimeters. The ocean analysis and forecasting systems used
here are those currently used by the Copernicus Marine Environment and
Monitoring Service (CMEMS) to provide operational services and ocean
reanalysis. The results obtained in the OSSEs considering along-track
altimeters were consistent with those derived from real data (observing
system experiments, OSEs). OSSEs can also be used to assess the potential of
new observing systems, and in this study the results showed that future
constellations of altimeters will have a major impact on constraining the
CMEMS ocean analysis and forecasting systems and their applications.