Training neural mapping schemes for satellite altimetry with simulation
  data
Quentin Febvre Julien Le Sommer Clément Ubelmann Ronan Fablet
Satellite altimetry combined with data assimilation and optimal interpolation
schemes have deeply renewed our ability to monitor sea surface dynamics.
Recently, deep learning (DL) schemes have emerged as appealing solutions to
address space-time interpolation problems. The scarcity of real altimetry
dataset, in terms of space-time coverage of the sea surface, however impedes
the training of state-of-the-art neural schemes on real-world case-studies.
Here, we leverage both simulations of ocean dynamics and satellite altimeters
to train simulation-based neural mapping schemes for the sea surface height and
demonstrate their performance for real altimetry datasets. We analyze further
how the ocean simulation dataset used during the training phase impacts this
performance. This experimental analysis covers both the resolution from
eddy-present configurations to eddy-rich ones, forced simulations vs.
reanalyses using data assimilation and tide-free vs. tide-resolving
simulations. Our benchmarking framework focuses on a Gulf Stream region for a
realistic 5-altimeter constellation using NEMO ocean simulations and 4DVarNet
mapping schemes. All simulation-based 4DVarNets outperform the operational
observation-driven and reanalysis products, namely DUACS and GLORYS. The more
realistic the ocean simulation dataset used during the training phase, the
better the mapping. The best 4DVarNet mapping was trained from an eddy-rich and
tide-free simulation datasets. It improves the resolved longitudinal scale from
151 kilometers for DUACS and 241 kilometers for GLORYS to 98 kilometers and
reduces the root mean squared error (RMSE) by 23% and 61%. These results open
research avenues for new synergies between ocean modelling and ocean
observation using learning-based approaches.