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Mapping altimetry in the forthcoming SWOT era by back-and-forth nudging a one-layer quasi-geostrophic model
  • +4
  • Florian Le Guillou,
  • Sammy Metref,
  • Emmanuel Cosme,
  • Clément Ubelmann,
  • Maxime Ballarotta,
  • Jacques Verron,
  • Julien Le Sommer
Florian Le Guillou
Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France, Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France

Corresponding Author:[email protected]

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Sammy Metref
Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France, Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France
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Emmanuel Cosme
Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France, Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France
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Clément Ubelmann
Ocean Next, Ocean Next
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Maxime Ballarotta
Collecte Localisation Satellites, Collecte Localisation Satellites
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Jacques Verron
Ocean Next, Ocean Next
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Julien Le Sommer
Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France, Université Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE; Grenoble, France
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Abstract

During the past 25 years, altimetric observations of the ocean surface from space have been mapped to provide two dimensional sea surface height (SSH) fields which are crucial for scientific research and operational applications. The SSH fields can be reconstructed from conventional altimetric data using temporal and spatial interpolation. For instance, the standard DUACS products are created with an optimal interpolation method which is effective for both low temporal and low spatial resolution. However, the upcoming next-generation SWOT mission will provide very high spatial resolution but with low temporal resolution. The present paper makes the case that this temporal-spatial discrepancy induces the need for new advanced mapping techniques involving information on the ocean dynamics. An algorithm is introduced, dubbed the BFN-QG, that uses a simple data assimilation method, the back-and-forth nudging, to interpolate altimetric data while respecting quasigeostrophic dynamics. The BFN-QG is tested in an observing system simulation experiments and compared to the DUACS products. The experiments consider as reference the high-resolution numerical model simulation NATL60 from which are produced realistic data: four conventional altimetric nadirs and SWOT data. In a combined nadirs and SWOT scenario, the BFN-QG substantially improves the mapping by reducing the root-mean-square errors and increasing the spectral effective resolution by 40km. Also, the BFN-QG method can be adapted to combine large-scale corrections from nadirs data and small-scale corrections from SWOT data so as to reduce the impact of SWOT correlated noises and still provide accurate SSH maps.
Apr 2021Published in Journal of Atmospheric and Oceanic Technology volume 38 issue 4 on pages 697-710. 10.1175/JTECH-D-20-0104.1