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MADT - Maps of Absolute Dynamic Topography & absolute geostrophic velocities

Types of dataset: Ssalto/Duacs gridded multimission altimeter products. 
Contents: gridded sea surface heights above geoid; dynamic topography is the sum of sea level anomaly (SLA) and mean dynamic topography (MDT), both being referenced over a twenty-year period in the Duacs 2014  version (V15.0). On this basis, the MADT is unchanged  since the ADT products have been calculated with consistent SLA and MDT field. If you compute MADT by your own ways, check that you compute MADT in a consistent way using the new 20-year reference period on Ref20yto7y page
Use: Ssalto/Duacs gridded products are devoted to scientific applications and non-commercial use: study of the general circulation (ocean gyres ...)
Condition of access : All Ssalto/Duacs product users need an account, see Access to Ssalto/Duacs data
Data access service: see Data access service. In NRT, FTP delivers the most recent data (day-0) whereas Opendap/geographic-temporal extraction tool/LAS only delivers data more than one month.
Description: gridded product, provided in near-real time and in delayed time. As a snapshot, each map represents the sea state for a given day. One spatial resolution is available: 1/4°x1/4° on a cartesian grid. 
This product contains absolute geostrophic velocities computed from absolute topography. 
Geographic coverage: global. A specific regional product with an improved quality is available in local areas (more information).
Format: NetCDF-CF


Description: this delayed time product is available in two versions:

  • "two sat merged" serie: this dataset is based on only two missions at most: Jason-2/AltiKa or Jason-2/Cryosat-2 or Jason-2 / Envisat  or Jason-1 / Envisat or Topex/Poseidon / ERS, with the same groundtrack. Thus it is homogeneous all along the available time period thanks to a stable sampling, but might not be the best in quality at a given time. The use of the "two sat merged" serie is mainly for application in need of great stability (but it must be kept in mind that the data might not be of the best possible quality). 
  • "all sat merged" serie: up-to-date datasets with up to four satellites at a given time, using all missions available at a given time. Sampling and Long Wavelength Errors determination are improved, so this serie is better in quality but not homogeneous over the time period. 

When only two satellites are available at a given time, the "two-sat-merged" and "all-sat-merged" files have the same content (files are duplicated).

The informations about the satellites taken into account are given in a new global attributes in the NetCDF file description (named "platform") and in the section "Temporal availability" of "Delayed-time Products" in the handbook

Copyright : 2005 - ongoing CLS - Cnes

Authenticated access service Frequency Data period File weight
Merged FTP 3-4 months From janv-93 to janv-16 2 MB per file (zipped)
Gridded Data Extraction Tool

Authenticated access service Frequency Data period File weight
Merged FTP 3-4 months From janv-93 to janv-16 2 MB per file (zipped)
Gridded Data Extraction Tool


Description : In NRT, FTP delivers daily the most recent data (6-day delay, a 3-day delay and a 0-day delay ) whereas Opendap/Gridded Data Extraction Tool/LAS only deliver data more than one month.
Data period : within a few months at most, from the latest update of the DT products to today.
Copyright : 2001-ongoing CLS-Cnes.

Authenticated access service Frequency Delivery delay Data period File weight
Merged (all available satellites) FTP Daily 0 day From janv-16 to today 2 MB per file (zipped)
Live Access Server 30 days
Opendap 30 days
Gridded Data Extraction Tool 30 days
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