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Ocean Science An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Jan 2019

Research article | 07 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

On the resolutions of ocean altimetry maps

Maxime Ballarotta1, Clément Ubelmann1, Marie-Isabelle Pujol1, Guillaume Taburet1, Florent Fournier1, Jean-François Legeais1, Yannice Faugere1, Antoine Delepoulle1, Dudley Chelton2, Gérald Dibarboure3, and Nicolas Picot3 Maxime Ballarotta et al.
  • 1Collecte Localisation Satellite, Ramonville-Saint-Agne, 31520, France
  • 2College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR
  • 3Centre National d'Etudes Spatiales, Toulouse, 31400, France

Abstract. The DUACS system produces sea level global and regional maps that serve oceanographic applications, climate forecasting centers, geophysics and biology communities. These maps are constructed from optimal interpolation of altimeter observations and are provided on a global 1/4°×1/4° (longitude×latitude) and daily grid resolution framework (1/8°×1/8° longitude×latitude grid for the regional products) through the Copernicus Marine Environment Monitoring Service (CMEMS). Yet, the dynamical content of these maps is not ensured to have a full 1/4° spatial and 1-day resolution, due to the filtering properties of the optimal interpolation. In the present study, we estimate the effective spatial and temporal resolutions of the newly reprocessed delayed-time DUACS maps (aka, DUACS-DT2018). Our approach is based on the spectral coherence between maps and independent datasets (along-track and tide gauge observations), which represents the correlation between two sea level signals as a function of wavelength. We found that the spatial resolution of the DUACS-DT2018 global maps based on sampling by three altimeters simultaneously ranges from ~100km-wavelength at high latitude to ~800km-wavelength in the Equatorial band and the mean temporal resolution is ~28 days period. The mean effective spatial resolution at mid-latitude is estimated to ~200km. The mean effective spatial resolution is ~120km for the regional Mediterranean Sea product and ~140km for the regional Black Sea product. An inter-comparison with former DUACS reprocessing systems (aka, DUACS-DT2010 and DUACS-DT2014) highlights the progress of the system over the past 8 years, in particular a gain of resolution in highly turbulent regions. The same diagnostic applied to maps constructed with two altimeters and maps with three altimeters confirms a modest increase of resolving capabilities and accuracies in the DUACS maps with the number of missions.

Maxime Ballarotta et al.
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Maxime Ballarotta et al.
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Short summary
This study investigates the resolving capabilities of the DUACS gridded products delivered through the CMEMS catalogue. Our method is based on the spectral coherence. While altimeter along-track resolves scales in the order of few tens of kilometers, we found that the merging of these along-track data into continuous maps in time and space leads to effective resolution ranging from ~ 800 km wavelength at the Equator to 100 km wavelength at high latitude.
This study investigates the resolving capabilities of the DUACS gridded products delivered...