BALTIC+ SEAL – Sea Level

The current knowledge of the water circulation in the Baltic Sea comes essentially from in situ observations and models. The Baltic+ SEAL (Sea Level) Project aims at providing a consistent description of the sea level variability in the Baltic Sea area in terms of seasonal and inter-annual variation and put the results in relationship with the forcing associated with this variability, using a developed dedicated coastal altimetry product. The objective is to create and validate a novel multi-mission sea level product in order to improve the performances of the current state-of-the-art of the ESA efforts in this topic: the Sea Level Climate Change Initiative (SL_cci). In this sense, this project can actually be considered as a laboratory in which advanced solutions in the pre-processing and post-processing of satellite altimetry can be tested before being transferred to global initiatives, such as the future phases of SL_cci.

The Baltic Sea includes the two main areas in which the use of satellite altimetry has been severely limited since the start of the “altimetry era”: the presence of sea ice and the proximity of the coast. During the winter season and the sea ice maximum in end of February, 40% of the Baltic Sea is covered by sea ice. The Team aims to apply an unsupervised classification approach to all possible altimetry satellite missions treated in this project (TOPEX-Poseidon, ERS-1/2, Envisat, Jason-1/2/3, SARAL/AltiKa, CryoSat-2, Sentinel-3A/B) to get reliable open water observations and adapt the classification approach to the sea-ice/open-water conditions and different satellite altimetry mission characteristics (e.g. pulse-limited, SAR).

The Baltic Sea area is also strongly impacted by Vertical Land Motion and in particular by the glacial isostatic adjustment. As it has the advantage of being an area very well sampled by tide gauges, which measure relative sea level, the Project aims at constituting a more reliable source to compare the absolute sea level from altimetry with the absolute sea level obtained by subtracting the Vertical Land Motion from the trends at the tide gauge and could even be the data source for experiments of differentiation between TG and altimetry trends in the absence of GPS measurements.