Mobile version

Otec: Ocean Topography of The English Channel

C. Le Provost, J.M. Molines (Legi/IMG, France)

The main purpose of Otec is to correct Topex/Poseidon measurements for tidal effects, as deduced from local models, and compare the corrected heights from one cycle to the next.

The Otec operation, part of the Aviso/Quick-look project [Le Provost, 1974; Le Provost, 1981; Le Provost, 1983; Le Provost & Fornerino, 1985] uses existing in-depth knowledge of tides in the Channel. In these coastal waters, variability in sea level is mainly due to very strong semi-diurnal tides, with tidal ranges up to 12 m at St. Malo on the French coast during spring tides. The general circulation and the weather have little effect.

From the tide model for the Channel we can forecast the instantaneous level to within 10 cm [Le Provost, 1983].
The along-track differences between cycles represent the cumulative orbital error, propagation corrections and tidal corrections. In the ideal case, with these errors zero, if we assume that the ocean signal contribution is negligible, we would have a perfect overlay of the corrected heights, giving the shape of the geoid along that track.

The passes over the Channel are passes 61, 137, 146 and 222 (Figure 1). In this article we refer to pass 61 only, at the western end. The data we used are the simplified files, version 1 IGDR-Ms, distributed as part of the Aviso/Quick-look project.

The corrections applied were: Doris ionospheric, closest dry tropospheric, TMR wet tropospheric, inverse barometer, CNES electromagnetic bias (Ku), earth tide and load effects. We did the calculation several times using different orbits: Cnes, Nasa and a Cnes (Aviso/Quick-look) orbit with 1-cycle-per-revolution and 2-cycles-per-revolution corrections by minimizing the rms values at crossover points.
Figure 2 shows the corrected heights on track 61 for cycles 1 to 9.

Figure 2a to 2d: Sea surface height for track 61, cycles 1 to 9:
a) Cnes orbit,
b) Cnes orbit with Aviso/Quick-­Look orbit correction,
c) Nasa orbit ,
d) Nasa orbit without inverse barometer correction

It turns out that:
- the results from the Nasa orbit are better grouped than those from the Cnes orbit,
- with the 1-cycle-per-revolution and 2-cycles -per-revolution orbital correction, the results of the corrected Cnes orbit are within a range of ±15 cm and therefore provide roughly the same quality as the Nasa orbit, with the exception of cycle 6,
- the inverse barometer correction is useful for grouping the results and we think it is appropriate for the area considered,
- thanks to this experiment we can gauge the final accuracy of the altimeter data distributed in the Aviso IGDR-Ms. The range of ±15 cm, encouraging in itself, should be noticeably reduced when the new orbits being computed at Cnes are ready.



  • Le Provost, C., 1974: Contribution à l'étude des marées dans les mers littorales. Application à la Manche. Doctoral thesis, Grenoble
  • Le Provost, C., 1981: A model for prediction of tidal elevations over the English Channel. Oceanologica Acta, 4, 279-288
  • Le Provost, C., 1983: An analysis of SEASAT altimeter measurements over a coastal area: The English Channel. J. Geophys. Res., 88, 1647-1654
  • Le Provost, C., M. Fornerino, 1985: Tidal spectroscopy of the English Channel with a numerical model. J. Phys. Oceanogr., 15, 1009-1031.
Rss feedsContactPartnersFAQLexiconLegal noticePersonal Data Protection PolicyMobile
You must enable cookies in your browser preferences to save the modifications
You are using an older version of Internet Explorer, please update to take full advantage of Aviso+ features

Customize the home page

View all widgets
Reduce display
Public profile
User profile

Select/Deselect widgets

Discover AVISO+

Customizable home, reading tools, products search guide, etc.. Discover step by step the features of the new site AVISO+.

Customizable homepage

This home page is composed of blocks called "widgets".

Rearrange the blocks with a "Click & Drop".

Hide a widget with the cross at the top right. Reset or add a widget with the "wrench" icon. The "User" and "Public" profiles offer a predefined organization.

All the modifications are automatically saved as cookies on your machine so as to enable you to have your own specific AVISO+.

Reading tools

Ease your reading by choosing the page background colour (black/white) and/or by modifying the font size.

Browsing menu and breadcrum trail

To ease your browsing through AVISO+, you can use at any time the main banner items with the interactive submenus or use the browsing menu on the left side of the screen (it is open by default). For more readiness of the page contents, you can fold and unfold the browsing menu by clicking on the tab. At any time you can know where you are thanks to the browsing menu or the breadcrum at the top of the page.

Products search guide

The first submenu of the "Data" banner item leads you to a new search form enabling you to find quickier the product that suits your needs. The list of results is updated according to your selection criteria.

AVISO+ Multimedia

The first submenu of the "Multimedia" banner item leads you to AVISO+ collections of images and videos linked to altimetry and its applications. Have a nice visit!