CTOH – 17 years of altimetric service
Rosemary Morrow(1) , Yves Menard(2) , Joel Sudre(1) , Mathilde Faillot(1) , Florence Birol(1) , Sylvianne Daillet-Rochette(2) , and Fabien Blarel(1)
18, av. E. Belin,
31401 Toulouse Cedex 9,
(2) CNES, 18, av. E Belin, 31401 Toulouse Cedex 9, France
The Centre de Topography des Océans et de l’Hydrosphère (CTOH) is a French National Observational Service dedicated to satellite altimetry studies, first established in 1989 to investigate ocean dynamics from Geosat data. The main objective of the CTOH is to maintain up-to-date, homogeneous altimetric data bases for studying long-term changes in the ocean sea level, or continental surfaces, with an emphasis on precise monitoring for climate studies. Our data bases provide support for scientists working on open-ocean processes, but also for the emerging fields of coastal satellite altimetry, satellite hydrography (over lakes and rivers), and the cryosphere. For these new altimetry applications, the standard altimetry products (which are tuned for open ocean conditions) are either absent or the data are not accurate enough.
Over the last 17 years, numerous altimetric corrections and algorithms have been developed by the research groups at LEGOS and validated and distributed as part of the CTOH/LEGOS activities. These include the retracking algorithms for the ERS/ENVISAT altimeters (ICE2 algorithm) (Rémy, Legresy); the tidal models and corrections of the FES1999, FES2002, FES2004 series (Le Provost, Lyard), the high-frequency barotropic correction of MOG2D (Lyard, Carrère), various improved corrections for maintaining maximum precision for global sea level studies (Cazenave, Minster, Le Provost), and specific algorithms for improving altimetric data quality and coverage in the coastal domain (ALBICOCCA project, Lyard, Roblou) and over lakes and rivers (Cazenave, Cretaux, Gennero). The CTOH maintains these up-to-date corrections from LEGOS and other research groups for all of the available altimetric missions, aiming for a rapid upgrade and distribution of its data products.
At CTOH, we currently maintain two types of altimetric data bases. For ocean and coastal sea level studies, and continental and cryosphere surface levels, we maintain GDR data products with up-to-date corrections from the Topex-Poséïdon, Jason, GFO and ENVISAT missions (1992 – 2006+). For the emerging applications in the coastal domain, over continental surfaces, lakes and river and over the cryosphere, we have a ERS/ENVISAT waveform data base retracked with the ICE2 algorithm for the entire ERS-ENVISAT period (1991 – 2006+).
Various data products are available, including alongtrack GDR data with the most recent corrections (MOD2D, FES2004, etc), global gridded surface currents from altimetry and scatterometry data (see poster Sudre and Morrow), retracked topography and surface roughness over the continental and coastal domains (see poster Legresy et al.). We are currently developing specific high-resolution products for the coastal zone (see posters Lyard et al.; Birol et al.). The CTOH also has an outreach mission in providing easy access to altimetric data products for internal and external scientific users, and also in providing training on the use of altimetric data, and the physical interpretation of the different altimetric components, for students, visiting scientists, and external users.
For more information see our new web site : http://www.legos.obs-mip.fr/en/observations/ctoh