ADT - Absolute Dynamic Topography (along-track)
Types of dataset: Ssalto/Duacs along-track multimission altimeter products
Contents: along-track 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 ADT is unchanged since the ADT products have been caluclated with consistent SLA and MDT field. If you compute ADT by your own ways, check that you compute ADT in a consistent way using the new 20-year reference period on Ref20yto7y page.
Use: study of the general circulation (ocean gyres ...)
Condition of access : All Ssalto/Duacs product users need an account on FTP, see Access to Ssalto/Duacs data
Data access service: Along-track products are only delivered through the authenticated FTP server.
Description: mono altimeter satellite product homogeneous with other satellites, available in near-real time and in delayed time.
Geographic coverage: global. A specific regional product with an improved quality is available in local areas (more information).
Description: this delayed time product is available in two series (which corresponded to the "Upd" serie in the former Duacs version, before April 2014. The "Ref" serie is no longer delivered):
- "filtered" serie (vfec) : validated + filtered + subsampled + correction for LW (long wavelengh) errrors product. Residual noise and small scale signals are removed by filtering the data using a Lanczos filter. As data are filtered from small scales, a sub-sampling is finally applied. As a consequence, for a given date, the distance between each measurement is bigger in a "vfec" file than in the "vxxc" file. Note that the filtering and sub-sampling is adapted to each region and product as a function of the characteristics of the area and of the assimilation needs (see details in the handbook, section "Filtering and Sub-sampling" for Delayed-Time products). Users that need to use a measurement with noise error reduced should rather user this filtered product.
- "unfiltered" serie (vxxc): validated + non filtered + non subsampled + correction for LW errrors. This product keeps the full 1Hz resolution. This means that for a given date, the number of measurements is bigger in a "vxxc" file than in the vfec file. Moreover, the uncorrelated measurement noise is not reduced (because of non filtering). Users that need the full 1 Hz measurements should use this unfiltered product keeping in mind that it is affected by the full 1Hz measurement noise error.
Copyright : 1993-ongoing CLS - Cnes
|Access service||Frequency||Data period||File weight|
|3-4 months||From mars-13 to Apr-14||700 Ko per file (zipped)|
|Cryosat-2||From Apr-12 to Apr-14|
|Jason-2||From oct-08 to Apr-14|
|Jason-1 (j1, j1g, j1n)||From Apr-02 to juin-13|
|Envisat (en, enn)||From oct-02 to Apr-12|
|ERS-1||From oct-92 to May-95|
|ERS-2||From May-95 to Apr-03|
|T/P(tp, tpn)||From sept-92 to oct-05|
Description : Only "filtered" version ("vfec", see description above) is delivered. FTP delivers daily the most recent data: the most recent file is updated several times per day in order to include the most recent available OGDR data (HY-2A not concerned).
Data period : within a few months at most, from the latest update of the DT products to today.
Copyright : 2004-ongoing CLS-Cnes.
||Frequency||Delivery delay||Data period||File weight|
|HY-2A||authenticated FTP: filtered||Daily||72 hours (best effort)||From juin-14 to today||350 Ko per file (zipped)|
|Saral||Daily||3 hours to 3 days||From Apr-14 to today||350 Ko per file (zipped)|
|Cryosat-2||Daily||3 hours to 3 days (best effort)||From Apr-14 to today||300 Ko per file (zipped)|
|Jason-2||Daily||3 hours to 3 days||From Apr-14 to today||2.5 MB per file (zipped)|