Mobile version

Different kinds of Duacs products

Merged data

Mesoscale structures represent typical space and time scale of 50 km to 500 km and 10 days to 100 days. Combining data from several satellites gives a better space/time resolution, and thus able a better mesoscale circulation observation.

EKE values were computed (EKE=1/2x(U²+V²), assuming geostrophic balance), using eleven months of delayed time four missions datasets: Jason-1, ERS-2/Envisat, Topex/Poseidon interleaved (T/Pi) and Geosat Follow-on (figure 1). It was then compared with a two altimeters "classical" configuration (figure 2).
Maximum EKE values correspond, as expected, to major ocean currents (Kuroshio, Gulf-Stream, Antarctic Circumpolar Current..). RMS differences between the two scenarios reach 400 cm²/s².

Reference/up-to-date historical datasets

While T/P, with its unprecedented accuracy, has provided a new picture of the ocean, it cannot observe the full spectrum of the sea-level and ocean circulation variations. Only a combination of several altimeter missions will resolve the main space and timescales of the ocean circulation.
Two satellite sampling is often assumed to be sufficient for mesoscale applications [Blayo et al., 1997]. Furthermore, the situation when merging 4 satellites has significantly improved the mapping capabilities as described in [Pascual et al., 2006]: at low latitudes (20°S-20°N) where the size of typical structures is quite large, the impact of the two additional altimeters is almost negligeable. On the contrary, in areas of intense mesoscale variability located at mid and high latitudes, the RMS differences between the 2 and 4 altimeter configuration are in between 5 and 10 cm, which represent an important percentage of the signal variability.
Now Delayed Time Ssalto/Duacs along-track and gridded products propose two sort of time series:

  • one is generated with a maximum of two satellites sampling (denoted "Ref" for "Reference"), where product's quality is homogeneous with time. This series is provided for long-term analysis of ocean signal with consistent values and for the analysis of large structures, in areas where ocean variability is weak
  • the other one is generated with up to 4 satellites avalaible at a given time (denoted "Upd" for "Up-to-date"); product's quality is improved, thanks to a better sampling, but not homogeneous. They are especially usefull when analysing areas of intense mesoscale variability, or specific period of time.

Global/regional products

Since 2005, new regional products are available; these products are not issued from a geographic extraction of parameters but result from a specific Duacs system component.

Atlantic and Gulf Of Mexico products provide sea level anomalies at full resolution i.e without any filtering, subsampling and nor long wavelenghts error corrections.
On the other hand for Mozambique area, Mediterranean and Black Seas products generation, data are filtered/subsampled/LWE corrected, with specific regional criteria.

Formal mapping error maps

Ssalto/Duacs products provide formal mapping error maps that represent error fields for sea level anomalies, using objective analysis.

A radar altimeter precisely measures the range from the radar antenna to the ocean surface.
Many errors affect the measurement of the range:

  • altimeter instrumental errors (altimeter noise),
  • errors associated to the travel of the pulse across the atmosphere,
  • orbit error.

In Ssalto/Duacs system, all these errors are reduced thanks to smoothing estimations, computation of atmospheric corrections (troposphere and ionosphere) and long-wavelength errors minimization via spline fitting and filtering.

The computation of the sea level along the altimeter tracks is also taking into account the oceanographic variations such as tides and pressure effects. Moreover, the error for the estimation of sea level along tracks depends on the latitude of the points. It is about 3 cm in deep ocean and can reach up to 7 cm near the coast or in semi-enclosed seas. The values near the coasts or in semi-enclosed seas depend on the accuracy of the corrections used (for example tidal model,...) above the regions observed.
Finally, for oceanographic applications, a mapping process based on objective analysis allows to product gridded sea level anomalies and corresponding formal mapping error fields over the global ocean.
Concerning geostrophic velocities, velocity errors also derive from SLA errors, added to some approximations due to geostrophic balance assumption. Those maps are expressed as a percentage of the signal variance allowing to estimate the relative error made by the mapping process.


High / low resolution maps

Duacs combined NRT-MSLA data are also available in filtered version ("low-resolution" NRT-MSLA). As they show large-scale ocean variation, they can be used in climate studies.

Flux RssContactPartenairesFAQLexiqueMobile
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

The new 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!