Coastal altimetry is a complex topic - the radar beam can reflect on a mix of water and land, thus the data must be processed differently from the open ocean --. Moreover, the coastal dynamics involve tides, potentially extremely jagged coastlines. The "high-resolution" along-track data ("20 Hz") are needed to get as close as possible to the lands. Cnes/CTOH/Legos/CLS/Noveltis published a new dataset last year, AltiCap, with 20-Hz dedicated processed Sea Level Anomalies "close" to the coasts (less than 500 km), from Jason-3 only for now.

A study made in the frame of a PhD at La Rochelle Université (west of France, on the coasts of the Bay of Biscay) is looking at those data in their neighbourhood. The "pertuis charentais" is a shallow area between the coast around La Rochelle proper and the islands (Ré, Aix and Oléron islands) with complex currents and tides. A number of in situ stations are available there (La Pallice (La Rochelle) and  Aix Island tide gauges, GNSS station at Ré and Oléron Islands), some for a long time, which enable to validate the altimetry data. The study aims to extend the time series to other altimeters, on the "reference mission" historical track (Jason-1 & 2, Sentinel-6 Michael Freilich), but also others missions overflying the area (Sentinel-3A, Saral), and Swot nadir.