Coastal zones

In a general way, the coastal oceanic dynamics is complex and is characterized by a wide range of dynamic processes answering in a strong way the local and distant forcing. The understanding and surveillance of the coastal oceanic regions are however major stakes for the questions relative to the ecosystems, the transfers of pollutants, the coastal development or the climate change.

These last years, the altimetry allowed tremendous headways in term of knowledge of the deep-sea ocean. The potential of this type of measure for the coastal (whether it is in term of documentation on the physics, model validation or assimilation in the models of coastal ocean) is very important but is currently unexploited. It is due to the standard altimetric products being badly adapted to these regions.

For the deep-sea ocean, the treatment of the signal and the corrections to be applied are well known and the height measurements of the sea are very precise. Near coasts, the precision decreases in a very important way to reach levels of error which can overtake 1 m. This is due to three types of causes: 1) The operational geophysic models used to correct the effects of tide and atmospheric forcing high frequency, are not adapted to the coastal physics and introduce important errors. 2) The standard corrections applied to the measure for landing in the disturbing effects of the atmosphere (effects of the ionosphere and troposphere) do not take into account the presence of the appeared lands. 3) Furthermore, the radar echo itself depends on characteristics of the observed surface and is modified by the presence of lands.

• At present, the CTOH develops altimetric products dedicated to the coastal domain. It is a question, in association with the scientific community, of developing, testing and validating:
• adapted geophysic corrections (tide correction, high frequency barotrope correction
• new correction algorithms of the measure to disinfect the datum of land presence (correction of the dry and wet troposphere, ionospheric correction)
• new reprocessing algorithms of the altimetric radar echos
• more precise average surface.

In view of testing and validating, experimental regions arranging number of study means (in-situ measures and model) were chosen, of which the Gulf of Lions region (Albicocca site) and the region of the Humboldt system. Once validated on these regions subjected to very different conditions, the treatment algorithms of the altimetric measure will be applied to other zones.

Besides, the coastal processes correspond to a wide range of spatiotemporal scale going of the kilometre to several hundreds of km, from the hour to the interannual. The CTOH also has for mission to develop the methodology necessary for the emergence of new products dedicated to the coastal by basing itself on the combination of information from altimetric observations and others type of measures.

New instruments more adapted to the observation of the coastal ocean have just been launched (SARAL/AltiKA mission, since 2013/02/25) or are under development (based on wide-swath altimetry technology as SWOT, planed for 2020). The CTOH also participates in the definition of these missions.