Improving information on ocean surface currents observed from space

Researchers at the Nansen Center and NORCE developed an algorithm that makes it possible to get more exact information on ocean surface currents, especially along the coast. 

Coastal areas can be difficult to navigate in. A new algorithm can be used to make it less difficult and more secure. Photo: Stein Egil LilandCoastal areas can be difficult to navigate in. A new algorithm can be used to make it less difficult and more secure. Photo: Stein Egil Liland

An ocean surface current is water being continuously moved in a direction, driven by winds along the surface. These currents are relevant for both science and for developing a sustainable blue economy: the renewable marine energy sector, fisheries, and aquaculture benefit from a better understanding of currents. And just as importantly, marine safety operations and the marine transport sector depend on exact information on these currents as well, as coastal areas can be especially difficult to navigate in. 

Getting information on ocean surface currents

Different kinds of measuring tools can gather information on ocean surface currents, such as drifting buoys or anchored moorings in the ocean, or land-based radars in coastal areas. But all tools have limitations and cannot supply accurate information over large areas. Satellites on the other hand have a fantastic view of oceans and coastal areas, making certain satellite data a good candidate to supply reliable information on those currents. The Synthetic Aperture Radar onboard the ongoing European Sentinel-1 mission sends a signal down to the ocean surface, which bounces back to the satellite. Researchers can use this information to identify the motion in the ocean by caused ocean surface currents. This process is not straightforward though, since the surface of the ocean is not only affected by surface currents, but also by waves and local winds. Therefore, these factors need to be removed from the data to get reliable information on the surface currents. Sounds fairly easy, doesn’t it? It is not, though. But Artem Moiseev and Johnny Johannessen at NERSC, together with Harald Johnsen (NORCE), found a way to improve the process to do so.

Improving that information

The recent publication by Moiseev and his co-authors, “Towards Retrieving Reliable Ocean Surface Currents in the Coastal Zone From the Sentinel-1 Doppler Shift Observations”, describes how they developed their algorithm and how it functions. Their algorithm takes both local winds and waves into account and makes it possible to remove their influence on the ocean surface currents. They focus on the challenging coastal areas and prove that their algorithm performs well there, too. In short, Moiseev and his colleagues succeeded in making information on ocean surface currents, retrieved from satellite data, more exact. Aside from benefitting scientific communities and supporting the development of a sustainable blue economy, their findings are relevant for space agencies such as the European Space Agency and the Norwegian Space Agency for evaluating ongoing and planning future missions in space.   

Reference:

Moiseev, A., Johannessen, J.A., and H Johnsen. Towards Retrieving Reliable Ocean Surface Currents in the Coastal Zone From the Sentinel-1 Doppler Shift Observations. Journal of Geophysical Research Oceans. 2022,127, https://doi.org/10.1029/2021JC018201

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