25 Years of Progress in Radar Altimetry OSTST

Ocean Next has participated in the symposium and annual meeting of the Ocean Surface Topography Science Team (OSTST), 24-28 september 2018, Ponta Delgada, Saõ Miguel Island, Azores Archipelago, Portugal.

Laurent Brodeau has presented a poster on “Mesoscale resolution capability of SARAL & Sentinel 3 altimeters with respect to kilometric-scale ocean simulations”. [Download]:


Abstract: The increase in mesoscale resolution capability of present generation altimeters is expected to further improve our understanding of the contribution of mesoscale processes onto ocean circulation, and to allow for a more reliable assessment of the ability of high-resolution ocean models to resolve these processes. In this context, the recent availability of data from submesoscale-permitting numerical simulations provides a very valuable source of information. Besides, recent studies, based on altimetry and numerical simulations, have highlighted the strong seasonality of the mesoscale activity at mid-latitudes as well as a pronounced spatial inhomogeneity at the basin scale. Therefore, assessing the mesoscale resolution capability of recent altimeter data; how it varies in space and time and how it relates to submesoscale permitting simulations, are questions that need to be addressed. In this study, the seasonal wavenumber power spectral density of SSH obtained from SARAL (KA band) and Sentinel 3 (delay-Doppler SAR mode) is calculated over a set of fourteen 10°⨉10° boxes spread over the North Atlantic and compared to that of the hourly SSH of a 1/60° resolution simulation with NEMO NATL60. For the model, both the SSH interpolated along the relevant satellite tracks (1D, subsampled) and the SSH over the whole box (2D, full resolution) are considered in our spectral comparison. Our spectral analysis shows that altimeter data agree well with synthetic data extracted from the model for wavelengths larger than the instrumental resolution capability. The results suggest that the typical resolution capability of the two altimeters is comparable and ranges from 70 up to 90 km (wavelength). Spectra of both the model and altimeter data confirm the substantial seasonality of (sub-)mesoscale activity in the North Atlantic. Moreover, our results show that the two approaches, based either on along-track-sampled (1D) or 2D model data yield very similar estimates of SSH wavenumber power spectra (energy level and slopes). Finally, our study suggests that carefully tuned submesoscale-permitting ocean circulation model simulations have the potential to become a powerful ally to extrapolate (below resolution capability scales)and interpret existing altimetry data and to prepare future altimeter missions (as for instance the upcoming SWOT mission). [DOI:10.13140/RG.2.2.25074.15048]