BALTIC+ Theme 3 Baltic+ SEAL (Sea Level) Scientific Roadmap.

For sea level studies, coastal adaptation, and planning for future sea level scenarios, regional responses require regionally-tailored sea level information. Global sea level products from satellite altimeters are now available through the European Space Agency’s (ESA) Climate Change Initiative. However, these global datasets are not entirely appropriate for supporting regional actions. Particularly for the Baltic Sea region, complications such as coastal complexity and sea-ice restrain our ability to exploit altimetry data opportunities.

The Baltic+ SEAL project has been framed as a laboratory to test advances in altimetry data processing to estimate sea level. It has developed a complete, replicable chain, from the treatment and flagging of individual echoes to the production of added-value products. The project activities also demonstrated the use of these new regionalised products, by conducting an examination of Baltic Sea regional sea level trend, calculating a new mean sea level map, and producing an experimental high-temporal resolution grid.

The Baltic+ SEAL project achieved the development of algorithms that can be applied to the entire constellation of altimetry missions, to significantly improve the quality and the quantity of sea level data available. Such techniques are easily exportable to other regions of interest. The released dataset, described in a dedicated product handbook, consists of multi-mission along-track data, gridded monthly sea level and mean sea surface. The sea level trend analysis performed within the project has highlighted the role of the North Atlantic Oscillation phases in shaping absolute sea level trend differences at a sub-basin scale. Further possible exploitation of the dataset includes a wide range of opportunities from supporting local ocean circulation research, to storm surge monitoring. As such, the project activities generated a wide range of new insights, products, best practices, scientific findings, and promotional material. These advances funded under the ESA Baltic+ programme represent the project foreground, which, if properly identified and managed, can maximise the impact of the project activities well beyond the end date of the project itself. This document outlines options for taking the scientific advances forward, in addition to a number of additional support activities which would maximise the impact of any future advances. The proposed suite of activities are framed by a context analysis, examining the sea level scene outside the Baltic+ SEAL project, in the coastal risk, and coastal altimetry arenas. The foreground generated by the Baltic+ SEAL project has also been mapped against this context. Finally the proposed scientific activities are proposed along with a first-estimate of costs, and mapped onto the context analysis to provide a measure of cost versus impact.

The advances under Baltic+ SEAL address a number of priority need areas identified by a context analysis using literature studies. These encompass the need to/for:
- Obtain measurements closer to the coast;
- Integrate more altimetry missions and cross-calibrate them;
- Customize approaches (highlighting the importance of regional and smaller scales); - Differentiate the coastal approach from the open ocean one, with coastal-dedicated approaches;
- Explore new instruments, and processing techniques;
- Integrate stakeholder engagement into advance efforts;
- Outreach about coastal altimetry;
- Departitioning / multi-disciplinarity (synergy) approaches;
- Compare the outputs of the various altimetry products;
- Enhance uncertainty information available with the data products.

A number of future scientific avenues for further research activity were identified and are proposed. These are supplied with a non-binding, preliminary estimate of their costs and timeframes. In addition, a range of (non-costed) support activities have been identified to run in parallel/synergy with the scientific activities, to maximise impact.