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Ocean Surface Topography from Space
Altimetry activities at the Centre de Topographie des Océans et de l'Hydrosphère (CTOH)


Rosemary Morrow - (LEGOS)

  Florence Birol
Fernando Nino
Sara Fleury
Denis Blumstein
Fabien Blarel
Mathilde Cancet


Altimetry activities at the Centre de Topographie des Océans et de l'Hydrosphère (CTOH)
(top panel) Global map showing regions where X-TRACK processing has been applied to develop regional data products, now distributed by the CTOH web site : (
(bottom panel) Number of visitors using the CTOH alongtrack data extraction website in 2011.
The CTOH is a French observation service dedicated to satellite altimetry, created in 1989 and supported by the CNRS, CNES, IRD and the Observatoire Midi Pyrenees. Its role is to facilitate access and use of altimetry data and products, to observe and study the dynamics of the oceans, the cryosphere and the hydrosphere. The CTOH has evolved to meet the growing needs of the scientific community and in support of the emerging altimeter applications (coastal, continental hydrology, cryosphere), which are associated with key scientific and societal issues (the link between the offshore and coastal water cycles, risk management ...).

This proposal over the Jason-II period will continue 1) to advance our user service for the ensemble of the CTOH data bases and products, 2) to extend the potential of satellite altimetry in the context of coastal marine studies, surface hydrology and cryosphere studies, and 3) to progressively transfer our research model products, expertise and services to SALP/AVISO, for an eventual extension into operational modes.

For the user services, the important developments concerns maintaining an up-to-date data base, including the most recent versions of the GDR data from each space agency, and validating and including up-to-date corrections as they become available. For the coastal zones, terrestrial surface waters and cryosphere, many of the standard corrections and even basic waveforms are not adapted. Ongoing studies will be made to test and incorporate new corrections and work on waveform algorithms adapted to the different missions (eg AltiKa in Ka band) and over the different surfaces (oceans, hydrology, ice).

Over the last few years, we have worked on extending our web services to allow external scientific users to access the ensemble of the GDR data and corrections, in order to develop their own products and applications, and help them use our existing products. This required an efficient data base access and specific web development. In the next four years, we plan to extend these services to other 2D data products, and to assist SALP/AVISO in setting up a similar, operational web-based data service for the alongtrack GDR data.

For the coastal studies, we are improving the Jason-II & Jason-I performance in regional applications (for both 1 Hz and higher sampling rate products), using the CTOH X-TRACK data processing, specifically designed for coastal studies. Regional validation of altimeter measurements from different missions (T/P, J1, J2, GFO, ENV, Cryosat-2, AltiKa) will also be performed at dedicated sites, as well as development of new regional products derived from altimetry data. For the surface hydrology studies, we provide the data for the Hydroweb service, and are setting up new waveform reanalysis over surface waters. For the cryosphere, echo and geographical corrections are being developed, and new products of continental snow coverage are being proposed from different satellite sensors.

Over the open ocean, multi-satellite data approaches are being developed to improve the mapping and representation of finer-scale structures in gridded regional maps. Lagrangian techniques are also used to recreate finer-scale structures in ocean tracer fields (eg temperature and salinity) using the lateral stirring from gridded altimetric currents. These have been developed in a number of test regions, and the technique will be extended to a global analysis, which may help improve the resolution of SMOS and Aquarius maps.

After validation, all of the regional products developed for the open ocean, coastal zones, hydrology surfaces and the cryosphere will be made publicly available through the CTOH web site. These developments will provide much greater availability of quality regional altimetry data and products to the oceanographic community.

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