See below the latest Ssalto/Duacs product changes and updates.

Before 2010, see the archives of changes in Ssalto/Duacs system.

• Ssalto/Duacs product changes and updates
• April 2013: Temporal extension up to November 21, 2012 of Ssalto/Duacs delayed time (DT) products
• February 2013: new version of Ssalto/Duacs V13.5: implementation of "OGDR on the fly" in NRT processing
• January 2013: Temporal extension up to July 18, 2012 of Ssalto/Duacs delayed time (DT) products
• December 4th 2012: Version 13.3 of SSALTO/Duacs: improvement of Cryosat-2 processing
• September 2012: Temporal extension up to April 18, 2012 of Ssalto/Duacs delayed time (DT) products
• 1st August 2012: Version 13.2.0 of SSALTO/Duacs: new altimetric standard version "D"
• Release of new regional products: Coastal DT SLA Jason-2
• June 2012: Temporal extension up to February 8, 2012 of Ssalto/Duacs delayed time (DT) products
• June 2012: Temporal extension up to December 7, 2011 of Ssalto/Duacs delayed time (DT) products
• May 25th 2012:Version 13.0 of SSALTO/Duacs: Integration of Jason-1 geodetic orbit in NRT products and stop of Envisat mission
• New release of Ssalto/Duacs NRT: v12.0.1
• April 2012: new format NetCDF-CF is the only available format for Ssalto/Duacs along-track products
• March 2012: Temporal extension up to September 2011 of Ssalto/Duacs delayed time (DT) products
• February 2012: Cryosat data available on Duacs
• January 2012: Erratum: Some along-track files corrupted for drifting missions (enn and e1)
• January 2012: Erratum on the last release Ssalto/Duacs Delayed-Time products
• January 2012: Modifications and Upgrade on the Opendap and the Extraction Tool
• January 2012, New Duacs NRT Along-Track regional products: Arctic and Europe
• December 2011: Temporal extension up to July 2011 of Ssalto/Duacs delayed time (DT) products
• October 2011: new version of Ssalto/DUACS v11.0.2 - RT and NRT Along-Track products improved
• September 2011: new release of seasonal/monthly means and climatology maps.
• September 2011: new release of DUACS v11.0.0 - NRT products mainly concerned
• July 2011: the series of daily Ssalto/Duacs gridded Delayed-time data has been extended to January 2011
• June 2011: the Ssalto/Duacs Delayed-Time products updated
• April 2011: Ssalto/Duacs gridded Delayed-time products now available for each day
• April 2011: the Ssalto/Duacs Delayed-Time products updated
• April 2011: update of Ssalto/DUACS NRT products v10.1.0
• March 2011: update of Ssalto/DUACS NRT products v10.0.2
• November 2010: Envisat back in Ssalto Duacs v.10
• November 2010: Important changes in the Ssalto/Duacs NRT and RT production systems
• September 2010: The Ssalto/Duacs Delayed-time products updated
• July 8, 2010: new Duacs NRT version v9.3
• June 2010: New, reprocessed, Ssalto/Duacs DT data and change of distribution policy
• 2010: MyOcean and change in Duacs data policy
• 2010: Duacs Delayed-Time reprocessing

Delayed-Time products (both versions "Reference" and "Updated") have been extended up to November 21, 2012. They are available via the ftp.aviso.oceanobs.com server with your login/password and also, for gridded products, via extraction tools with specific login/password.

The monthly means have also been updated.

Note that for gridded products, this update only concerns the "weekly products" (i.e. one file produced by week), the "daily products" (i.e. one file produced every day) Delayed-Time products are not concerned by this update. Indeed, this production is experimental and temporary but could be permanent if you show us its value for your works: contact us! (By email to aviso(at)oceanobs.com, quoting "Feedback about the daily gridded DT production")

As you may know, since September 2011, the production of Global Along-track Real Time products called "OGDR on the fly" is performed experimentally (see our news ). The Duacs processing chain delivers via ftp the most recent available data in "global/rt/sla" and "global/rt/adt" directories several times per day. The generation of these products consists in completing the Global Along-track NRT products with the latest OGDR data received.

 
The Aviso team is pleased to inform you that, as from February 12th, 2013, the delivery of such products will now be done directly in the Near-Real time directories (double dissemination until February 28). Indeed, the Global Along-track NRT products (for Jason-1 and Jason-2 missions) will be updated several times per day in order to include the most recent available OGDR data.

For example, if you download files from global/nrt/sla/j1g_cf or j2_cf or global/nrt/adt/j1g_cf or j2_cf directories at 15:00 for the day D:

• at the present time, the last date of data that you can get in the last file delivered is ~20:00 of the day D-1.
• as from February 12, the same file will be updated and a new one created and updated and you will get data until 13:00 of the day D at the best (if OGDR is valid).

Along-track NRT Cryosat-2 and Gridded NRT products are not concerned. There is no impact on the scientific quality of the products.

As already mentionned, a double dissemination until February 28 is foreseen allowing you some time to change your scripts; this means that until February 28, the "rt" directories don't change and they will be erased after this date. You will find "OGDR on the fly" data in:

Example

for the example of the process on 2013-01-15, in file global/nrt/sla/j2_cf/nrt_global_j2_sla_vfec_20130114_20130114_20130115.nc.gz, the date of the last measurement is 2013-01-14 19:35:42

this file was created when the process began at 22:30 on January 14.

If the new version of Duacs was running:

• a new process would have begun around 2:00 on January 15 and the file nrt_global_j2_sla_vfec_20130114_20130114_20130115.nc.gz would have been updated and would have contained data until 2013-01-14 23:59
• a new process would have begun around 6:00 on January 15 and the file nrt_global_j2_sla_vfec_20130115_20130115_20130115.nc.gz would have been created and would have contained data until 2013-01-15 4:00
• a new process would have begun around 8:00 on January 15 and the file nrt_global_j2_sla_vfec_20130115_20130115_20130115.nc.gz would have been updated and would have contained data until 2013-01-15 6:00
• and so on...

The chain runs 1 to 10 times per day if new OGDR data is available.

So if you get files during the day, you will need to get 22 files nominally, the last two files being updated compared the current situation. Note also that some older files (not more than 3 days) can be updated if new IGDR data arrive and erase older OGDR data (a flag indicates in the file the input data: 1 for IGDR and 0 for OGDR).

Delayed-Time products (both versions "Reference" and "Updated") have been extended up to July 18, 2012. They are available via the ftp.aviso.oceanobs.com server with your login/password and also, for gridded products, via extraction tools with specific login/password.

This update takes into account

• the integration of Jason-1 on its geodetic orbit: the last date available for "j1n" is March 7, 2012 and "j1g" is a new mission beginning on June 12, 2012
• the new version "D" of Jason-2 input products (GDRs) since June 18, 2012 (complete information on version D)
• the end of Envisat mission on April 8, 2012

The monthly means have also been updated.

Note that gridded "Daily" Delayed-Time products are not concerned by this update. This production is experimental and temporary but could be permanent if you show us its value for your works: contact us! (By quoting "Feedback about the daily gridded DT production")

This new version improves the processing of Cryosat-2 data:

• a better tuning of altimeter parameter and correction (backscatter coefficient and thus the Sea State Bias correction)  improving the SLA stability,
• a new editing process allowing to improve the SLA quality notably in sea ice areas.

You can find information in Labroue S., A. Ollivier, M. Guibbaud, F. Boy, N. Picot, P. Féménias, “Quality assessment of Cryosat-2 altimetric system over ocean”, OSTST 2012 in venice 

The nomenclature, format, ... remains unchanged. This will have a scientific impact (see poster) on the Near Real Time global and regional Along Track Cryosat-2 products (nrt/sla/c2_cf and nrt/adt/c2_cf) as well as Near Real Time global and regional gridded merged products (nrt/msla/merged and nrt/madt/merged).

Delayed-Time products (both versions "Reference" and "Updated") have been extended up to April 18, 2012. They are available via the ftp.aviso.oceanobs.com server with your login/password and also, for gridded products, via extraction  tools with specific login/password.

This update takes into account the integration of Cryosat-2 data into Delayed Time products.

Note that gridded Delayed-Time products with daily temporal resolution are not concerned by this update. This production is experimental and temporary but could be permanent if you show us its value for your works: contact us!  (By quoting "Feedback about the daily gridded DT production")

Altimetric data are regularly reprocessed in order to take into account new algorithms, corrections, parameters, etc. Since its launch in June 2008, Jason -2 products have been disseminated in version "C". For Jason -2, it is now time to change for another standard to benefit from many years of progress in altimetry.

Main differences between versions "C" and "D" are described in the links below.

Further information:

• [Jason-2]: Information about the new altimetric standard version "D"
• Ssalto/Duacs User Manual: M( SLA ) and M( ADT ) Near-Real Time and Delayed-Time 

Delayed-Time products (both versions "Reference" and "Updated") have been extended to February 8, 2012. They are available via the ftp.aviso.oceanobs.com server with your login/password and also, for gridded products, via extraction  tools with specific login/password.

Note that gridded Delayed-Time products with daily temporal resolution are not concerned by this update. This production is experimental and temporary but could be permanent if you show us its value for your works: contact us!  (By quoting "Feedback about the daily gridded DT production")

Delayed-Time products (both versions "Reference" and "Updated") have been extended to December 7, 2011. They are available via the ftp.aviso.oceanobs.com server with your login/password and also, for gridded products, via extraction  tools with specific login/password.

Note that gridded Delayed-Time products with daily temporal resolution are not concerned by this update. This production is experimental and temporary but could be permanent if you show us its value for your works: contact us!  (By quoting "Feedback about the daily gridded DT production")

A new release of Duacs (version 13.0) was installed and activated on the production servers from May 25, 2012. 

• Integration of Jason-1 on its geodetic orbit since May 7, 2012 in NRT products.
• Stop of Envisat data in the processing

Complete information can be found in the operational news

A new release of Duacs (version v12.0.1) has been installed and activated on the production servers from April 03, 2012. Here are the updates:

• For along-track products in Near-Real Time and Real-Time, the old format NetCDF is definitively replaced by the new format NetCDF CF, as announced since September 2011.
• For Near-Real-Time maps in Mediterranean Sea (gridded products), improvement of the coverage in the Alboran Sea, the Marmara Sea and near the coasts.

As announced since September 2011 and in several reminders sent by emails, the old format NetCDF is definitively replaced by the new format NetCDF CF for all along-track products in Delayed-Time, Near-Real Time and Real-Time

NB: CorSSH and SLA monomission are not yet concerned by this new NetCDF CF format.

Delayed-Time products (both versions "Reference" and "Updated") have been extended to September 2011. They are available via the ftp.aviso.oceanobs.com server with your login/password.

Note that gridded Delayed-Time products with daily temporal resolution are not concerned by this update. This production is experimental and temporary but could be permanent if you show us its value for your works: contact us!  (By quoting "Feedback about the daily gridded DT production")

Duacs data derived from the Esa mission Cryosat-2 will be delivering by Cnes on February 06^th . All near-real time multi-mission products from Duacs [1] will be exploiting 4 altimeters (Jason-2, Jason-1, Envisat and Cryosat-2).

This major change is the result of the long-standing and fruitful partnership between Esa and Cnes and a response to the request from scientific and operational oceanography users [2].

The Duacs multi-mission system will be ingesting data flows generated by Cnes' Cryosat Processing Prototype (CPP) which are derived [3] [4] from Level 0 data flows from Esa. The CPP processor includes a pseudo-LRM handling of Cryosat's innovative SAR mode [5]. Duacs will therefore benefit from a full global coverage of the Cryosat-2 altimeter. This coverage notably includes European Seas, the Agulhas area, and high latitudes latitudes (up to 89° for the first time ever).

However please note that all Cryosat products from Cnes are generated within 24 to 48 hours on a best effort basis, and that Cryosat has a higher error budget than other altimeters because of its cryosphere-oriented design (no radiometer, no dual frequency ionosphere, drifting orbit) [6]. Yet no major anomaly nor delay has been identified on the Duacs test system since November 2011.

Further information:

• [1] Duacs data: Level 3 along-track SLA, and Level 4 multi-mission mesoscale maps, both global and regional.
• [2] Following the scientific recommendations from the OSTST meeting (San Diego, October 2011), the ESA Cryosat Project and the CNES SALP Project have been collaborating to generate these Cryosat-derived L3 and L4 products. Level 1B and Level 2 products derived from CNES processors are not distributed by AVISO as per the CNES / ESA agreement.
• [3] Picot.N., F.Boy (2011): CryoSat Processing Prototype, LRM Processing on CNES Side and a Comparison to DUACS SLA. Proceedings of the 2d Cryosat Validation Workshop (Frascati, 2011
• [4] Labroue.S et al (2011): First Quality Assessment of the CryoSat-2 Altimetric System over Ocean. Advance in Space Research (In Press). http://dx.doi.org/10.1016/j.asr.2011.11.018
• [5] Boy.F et al (2011): Cryosat LRM, TRK and SAR processing. Presented at the 2011 Ocean Surface Topography Science Team meeting (pdf).
• [6] Dibarboure et al (2011): A demonstration of the potential of Cryosat-2 to contribute to mesoscale observation. Advance in Space Research (In Press). http://dx.doi.org/10.1016/j.asr.2011.07.002
• [7] Esa website: How to access to Cryosat data
• [8] NOAA/NESDIS LSA CryoSat Interim Geophysical Data Record (IGDR)
• [9] Bouzinac et al, 2011: New CryoSat Ocean Products, Presented at the 5th Coastal Altimetry Workshop (pdf).

An anomaly has been detected in the along-track files of drifting orbit missions (ERS-1 during years 1994-1995 and Envisat on it new orbit: ENN). They have been replaced on the authentified ftp by the new files with the production date of 20120116 (the last date in the name of the files).
If you have already downloaded the files listed here, please download them again on the ftp.

The error is due to a problem in the numbering of the cycles in computation of along track products. Therefore, in all the files listed, there was an anomaly in the numbering of the cycle for the last track of one cycle (pass 1002 for ERS-1 and pass 862 on Envisat). Note that the corresponding dates and measurements were correct.

Some data files released during the last Ssalto/Duacs Delayed-Time temporal extension (see December 2011: Temporal extension up to July 2011 of Ssalto/Duacs delayed time (DT) products below) appeared to be erroneous and are now corrected.
Indeed, the coordinates grid (lon/lat) was not well defined and may cause an erroneous reading with some softwares (whereas others sofwares are not impacted).

If you have already downloaded the files for the data period between 2011/01/12 and 2011/07/06 (or in other words for all the production date of 2011/12/08), please check them with the softwares you use: Delayed-Time, updated and reference series for Global area in Maps of Sea Level Anomalies for the height and formal mapping error variables, with a weekly resolution (the MSLA with a 1/4° and 1° spatial resolution, respectively the filenames with *msla_h_qd* and *msla_h_lr*; and the geostrophic velocities UV are not concerned). In details, the following folders and files were impacted: 

• /global/dt/ref/msla/merged/h/, data files between
  • dt_ref_global_merged_msla_h_20110112_20110112_20111208.nc.gz and
  • dt_ref_global_merged_msla_h_20110706_20110706_20111208.nc.gz
• /global/dt/ref/msla/merged/err/, data files between
  
  • dt_ref_global_merged_msla_err_20110112_20110112_20111208.nc.gz and
  • dt_ref_global_merged_msla_err_20110706_20110706_20111208.nc.gz
• /global/dt/upd/msla/merged/h/, data files between
  
  • dt_upd_global_merged_msla_h_20110112_20110112_20111208.nc.gz and
  • dt_upd_global_merged_msla_h_20110706_20110706_20111208.nc.gz
• /global/dt/upd/msla/merged/err, data files between
  
  • dt_upd_global_merged_msla_err_20110112_20110112_20111208.nc.gz and
  • dt_upd_global_merged_msla_err_20110706_20110706_20111208.nc.gz

If you have encountered some difficulties to plot these last files, we invite you to download again the new corrected files that the production date is 2012/01/16 (which is the third date in each filename), on the authenticated data access services.

Since October 2011, the Ssalto/Duacs Delayed-Time MSLA and MADT were integrated through the Opendap with the daily resolution (by default, the weekly resolution was also included in this dataset).

In order to integrate to the Opendap and the Extraction Tool, the latest DT extension made on the ftp server for weekly products (extension up to July 2011), a new dataset is created to offer at once the weekly and the daily resolutions. The daily resolution is integrated in a new dataset whereas the old dataset contains only the weekly resolution  (see table below for the detailed filenames).
The temporal extension of these two datasets are different since the daily resolution was made as an experimental and temporary production and therefore, it is not upgraded at each Delayed-Time extension: 

Finally, an upgrade on the Extraction Tool enables to offer a new service. On each last page where you can download the data (after you have defined your own dataset), a new "script" button allows you to access on Python script command lines that matches the current extraction. These command lines help you to make your own script from the shell of you system (Linux/Unix/window).

Further information:

• Data access services: Authenticated Opendap and Extraction Tool
• If you are not registered and want to access those services (NB. for scientifc uses only), we request you to fill in the online form: http://www.aviso.oceanobs.com/en/data/registration-form/

Two new Duacs regional products are released on Wednesday, 11th January 2012: Arctic Ocean and Europe area, for addressing the needs of data assimilation and validation in regional models.
Those new products include Along-track multimission Sea Level Anomalies data in Near-Real Time.
They are delivered via authenticated FTP (see Access to Ssalto/Duacs products). If you already have an FTP account, your access is automatically updated; this means that no new subscription is required.
The data are in the following folders: regional-arctic/ and regional-europe/ .
The Geographic coverage includes:

• for Arctic area, an enlarged Arctic Ocean : 45°N-82°N / 0°-360°E
• for Europe area: 21°N-66°N / -25°W-42°E (Iberic-Biscaye-Ireland and Northwest shelves areas ; Baltic, Mediterranean and Black Seas).

Following the initiative launched by TAPAS (Tailored Altimeter Product for Assimilation Systems) in the MyOcean project with all the Modeling and Forecasting Centers (MFCs), the Europe regional products has been processed with adapted filtering and resolution. Those parameters as well as the coverage have been tuned in order to provide boundary conditions for the Atlantic assimilation models.
Indeed, the Europe area includes, among others, the Mediterranean and Black Seas which already belong to dedicated regional products (in regional-mfstep and regional-blacksea folders). However, note that if you need to study the Mediterranean or the Black Sea, you'd better use the dedicated regional products since the processing parameters have been fitted to be adapted to the dynamics of the ocean in those regions, which is not the case for the Europe product.
Nomenclature, temporal availability, product generation or corrections applied can be retrieved in the Ssalto/Duacs User Handbook.

Delayed-Time products (both versions "Reference" and "Updated") have been extended to July 2011. They are available via the ftp.aviso.oceanobs.com server with your login/password.

Note that gridded Delayed-Time products with daily temporal resolution are not concerned by this update. This production is experimental and temporary but could be permanent if you show us its value for your works: contact us! (By quoting "Feedback about the daily gridded DT production")

A new release of DUACS (version 11.0.2) has been installed and activated on the production servers from October 19, 2011. Here are the improvements:

Better accuracy of Envisat data at high latitudes

Since orbit Envisat is on a drifting orbit, the Mean Sea Surface (MSS_CNES_CLS_2011) is used to calculate the Envisat Along-Track SLA. Although the MSS is defined over the global ocean, its accuracy is reduced on the high latitudes areas due to the lack of altimeter measurement which does not allow constraining the MSS to incorporate the medium/small scale, representative of the mean dynamic circulation. In this case the MSS was only based on the geoid. The improvement of this new release of DUACS consists on a specific editing that removes erroneous measurements on these areas.

The OGDR processing has been improved

Thanks to the vigilance of a user, a minor anomaly on the NRT products has been detected (IGDR data are not impacted). To solve this problem, the OGDR filtering has been improved to better reproduce the mesoscale signals. Therefore the overall NRT products are of better quality.

Find further explanations in the DUACS user guide.

The monthly means, seasonal means and climatological Maps of SLA have been reprocessed using the extended delayed-time maps in daily temporal resolution (instead of weekly maps in the past - see the related topic). The areas concerned are global ocean, Mediterranean and Black Seas.

This processing provides finest averages and extends the monthly mean and climatological maps up to January 2011.

The file metadata has been adjusted to match with the NetCDF standard, used by most reading software for altimetric data as BRAT, ncBrowse, etc.

To access these products, please refer to the dedicated web pages:

Global

Mediterranean Sea

Black Sea 

A new version of Duacs (version 11.0.0) has been installed and activated on the production servers from September 14, 2011. Here are some notable upgrades:

• New format for the along-track products in Near Real-Time
• New Real-Time products on OGDR flow reception
• Integration of the GOT4.8 tides model for the along-track and gridded products
• New MSS CNES/CLS 2011 for Envisat products

New format for the NRT Along-track products

This new Duacs version provides along-track data in Near Real-Time with a new format following the standard NetCDF CF-1.4 (Climate and Forecast), making their use easier. Further information about this format at http://cf-pcmdi.llnl.gov/.

For both formats, in Near Real-Time mode, a maximum of 21 days of data are still processed and delivered but products in the new format CF are now daily (i.e. a single file contains 24 hours data while an old format file contains 21 days data).
Example: the old format data in the file 'nrt_global_j2_sla_vfec_20110825_20110914_20110915.nc' are contained in 21 different new format CF files:
'nrt_global_j2_sla_vfec_20110825_20110825_20110915.nc'
'nrt_global_j2_sla_vfec_20110826_20110826_20110915.nc'
...
'nrt_global_j2_sla_vfec_20110914_20110914_20110915.nc'

For both modes (NRT and DT), filename nomenclature, paths and access rights are the same: the new format CF files are stored in folders suffixed with "_cf" at the same levels as folders containing older format files. Example: in the FTP folder 'global/nrt/sla/', folders j2/ and j2_cf/ contain respectively data in the old format and new format CF for the Jason-2 mission.

This new format has no impact on the scientific content.

Note that DUACS NRT and DT products with the old format will still be distributed until the end of January 2012, leaving you time to adapt to the new format CF. Beyond that date, the new format CF will be the only available format for both modes (NRT and DT); be sure to be kept informed of such an operation.

Production of new Real-Time products 'OGDR on the fly'

In the previous Duacs production chain (v10.1.0), the OGDR data received during the day were included in products when the production starts, i.e. about 22h30 UTC. Consequently, depending the time at which the user wanted to get these data, the most recent ones could be missing.
To meet this need, the DUACS production chain now generates new RT product called 'OGDR on the fly'. The generation of these products consists in completing the Along-track products with the latest OGDR data received [see diagrams explaining].

In summary, to get the most recent data, just combine the latest NRT daily files (available in nrt/ FTP folders) with these RT products. Only the global product is concerned for the moment and OGDR on the fly data are stored in the FTP folder 'global/rt/'.

Correction of the GOT4.8 tides model

GOT4.8 is the latest version of tides model. This model has been integrated into the NRT Duacs products (both along-track and gridded). Concretely, the products taking advantage of GOT4.8 version are the NRT products with the two formats (see section above 'New format for products DUACS Along-track') and whose production date is later to September 14 ('Duacs v11.0.0' version) while products prior to this date and the release DUACS v11.0.0 include the model GOT4.7.

New MSS CNES/CLS 2011 for Envisat

Due to the Envisat orbit change, the Sea Level Anomalies (SLA Envisat) have to be derived from the Mean Sea Surface instead of Mean Profile and repeat track analysis (see news "November 2010: Envisat back in Ssalto Duacs v.10")

The new version of MSS (MSS_CNES_CLS2011) is now applied to NRT Along-Track Envisat products whose production date is later to September 14. For more information, see the MSS web page.

The gridded Delayed-Time products computed with a daily temporal resolution are now available until January 19th, 2011 (instead of March 31rd, 2010 before this reprocessing). The concerned products are the two processing series ("ref" and "upd") of MSLA and MADT data for the global and Mediterranean Sea, MSLA data for the Black Sea.

You can now access to these daily maps with your usual login/password if you've already a FTP account. If not, please fill in the registration form.

This production is still experimental and temporary but may be permanent if you show us its value for your works: contact us ! (please quoting "Feedback about the daily gridded DT production" ).

All the Delayed-Time products (both versions "Reference" and "Updated") have been updated. The latest DT maps and along-track files are now dated the January, 19th, 2011 on the ftp server.

Motivated by the fact that the weekly resolution used so far for DT maps was insufficient wherever the time decorrelation scale is close to 15 days, the gridded Delayed-Time products have been computed with a daily temporal resolution using the same DUACS processing system than before.

So now, for each day from October 14th 1992 to March 31th 2010 and for global, Black Sea and Mediterranean Sea, there are maps representing the sea surface anomalies and absolute dynamic topography (products called MSLA and MADT) while up to now, the snapshots were produced every 7 days.

You can now access to these daily maps with your usual login/password if you’ve already subscribed to get them. If not, please fill in the registration form.

This production is experimental and temporary but may be continued if you show us its value for your works: contact us ! (please fill in the subject with "Feedback about the daily gridded DT production" ).

All the Delayed-Time products (both versions "Reference" and "Updated") have been updated. The latest DT maps and along-track files are now dated the December 1st, 2010 on the servers.

Note that a delivery of updated gridded DT products with a daily temporal resolution will be made soon ...

This new version includes a few minor corrections which have a very small impact on DUACS NRT data quality. Please, find below some explanations about these improvements:

• Correction of flag values allocation for NRT SLA products:
  A new flag was added for last update mid-November in order to determine the origin of data between the different types of geophysical data records (GDR) used in computation of the SLA. This flag had some problems that have been solved within this version.
  Now, the flag_values takes the value 1 for the Interim GDR (IGDR) and 0 for Operational GDR (OGDR).

• New Google Earth products:
  In order to be accessible by anyone, new maps in Google Earth format are available via Aviso web page section 'Visualize the data' on the right.
  These files in .kmz format contain:
    - graphical mapping of the latter MSLA data produced and of MADT one (if any).
    - Ground tracks of the satellites used in the computation of the gridded data and tracks expected in the coming days.

• Minor correction of the CNES/CLS09 v1.1 MDT:
  A local default in this file has been corrected; it concerns only one pixel with invalid value and located on an island on the coast of Ecuador called "Isla Punà" (coordinates 80°08' W, 2°47' S)

Note that respective NRT MADT products were not reprocessed considering the low impact of a pixel data and its position.  

As mentioned in earlier messages, Envisat has been recently moved to a new orbit and to a different ground track. The dissemination of the first Envisat data on its new track started in early November, but as a conservative measure, Envisat processing in DUACS had been stopped until today. 

First of all, the analyses of Envisat data on the new orbit exhibit no major instrumental anomaly on Level 2 Sea Surface Height data from ESA.

Second point is that the orbit change means that in place of a Mean Profile and repeat track analysis, Envisat sea level anomalies must be derived from a gridded Mean Sea Surface. This is made possible by the recent improvements of recent gridded MSS (CNES/CLS10, DTU10, DNSC08). However, using a gridded MSS in place of a precise along-track reference involves additional errors. Various analyses were recently performed and presented to the Ocean Surface Topography Science Team. We think the error on DUACS products is not a showstopper, but not a trifle either.

Considering the large improvements associated with an additional satellite in Near Real Time, we decided to re-activate Envisat processing in Near Real Time. The good sampling complementarity between Envisat and the Jason tandem, and the good instrumental behaviour of Envisat largely outshine the degraded accuracy linked to local MSS imperfections.

However, we strongly encourage DUACS users not to take along-track Envisat data for granted, and to analyze them in details.
We also encourage users of DUACS' along-track SLA to increase the error prescribed (e.g. in assimilation) on ENVISAT SSHA by 2 to 3 cm rms (ideally with higher errors in coastal areas or at high latitudes, where the gridded MSS used is likely less accurate) in order to mitigate the impact of artificial mesoscale signatures (e.g fake stationary eddy) created by gridded MSS residuals errors.

As per usual, any feedback on recent Envisat products is welcome to try and improve the processing of Envisat in DUACS.

For more information see Envisat_back_in_Ssalto_Duacs v10 

In September 2009, a new timeliness dataset was released (Ssalto/Duacs v9.1.0). Based on the enhanced OGDR+IGDR production, this RT production system exploits the most recent datasets available to produce multi-missions maps with 0-day and 3-day delay.  This RT production has showed a better resilience, a better precision of the system and a better restitution of ocean variability especially in high energetic areas.

By taking into account these advantages and since it has been running nominally long enough, this RT sub-system will replace the historical IGDR-based NRT sub-system from November 15th, 2010. Nevertheless, during a provisional time (one month), the NRT and RT sub-systems  both  will be supplied in parallel. This change will be entirely effective on December 15^th, 2010 where:

• the old RT production is placed in the nrt/ directory, to become the new NRT production.
  A new flag included in the along-track products will indicate the source of the production (OGDR or IGDR). If flag=1, the processed data comes from OGDR; if flag=0, the processed data comes from the IGDR.
• the NRT production based on the only IGDR production disappears,
• the rt/ directory won’t be updated and then, it will disappear,

This change in the NRT and RT production systems occurs just after the Envisat orbit manoeuvres in order to include the changes of the new Envisat phase in the Ssalto/Duacs system (see our news Envisat Orbit change impacts on Duacs):

• change in the nomenclature:  "EN" will be replaced by "ENN" in all file and directories names  to take into account the change of orbit,
• a new repetitive ground track will be used: 30 days with 431 orbits per cycle instead of 35 days-501 orbits per cycle,
• no mean profile for the Envisat track can be used. The alternative is to use the Mean Sea Surface instead (MSS_CNES_CLS10).

Further information in the Ssalto/Duacs user's handbook.

All the delayed-time products (both versions "Reference" and "Updated") have been updated. Latest maps and along-track files are dated the 30^th of March 2010 on the servers.

The latest version of the Duacs-NRT software (v9.3.0) has been installed and activated on the production servers.

Here are some notable upgrades:

• a new Mean Dynamic Topography, MDT_CNES-CLS09 is taking into account, allowing to better represent the velocities of geostrophic currents. Note that this new MDT is not referenced to the same level than the previous one, thus MADT values change,
• improved velocity estimate from the MDT in the equatorial band,
• the Long Wavelength Error is computed during the mapping process, allowing to improve the level-4 products (MSLA),
• by using the new mean profiles, new along-track SLA products are computed,
• new corrections and models are applied (tides, Sea State Bias, etc). See tables 3 et 4 in the Ssalto/Duacs User Handbook.

The latest version of the Ssalto/Duacs-DT software (v3.0.0) has been installed and activated on the production servers. As we first announced the Aviso data falls under the new data policy ((see below 2010: Duacs Delayed-Time reprocessing). The reprocessed Ssalto/Duacs DT data aren't distributed anonymously as older products were. To get access to these new reprocessed data, you have to fill in the registration form on: http://www.aviso.oceanobs.com/en/data/registration-form/index.html.

These new reprocessed DT series are streched out as fas as the 04^th of November 2009.

See illustrations and more details on the parameters used for the Ssalto/Duacs DT-(v3.0.0) products generation and their impact on the product quality on: Ssalto/Duacs reprocessed DT data set (pdf).

What is MyOcean?

Here is an excerpt from the project description. Feel free to get more information on the project website.
http://www.myocean.eu.org/
MyOcean is the implementation project of the GMES Marine Core Service, aiming at deploying the first concerted and integrated pan-European capacity for Ocean Monitoring and Forecasting.
During years 2009-2011, thanks to FP7 co-funding, MyOcean will lead the setting up of this new European service, grown on past investments in research & development, system development and international collaborations.
MyOcean Service provides the best information available on the Ocean for the large scale (worldwide coverage) and regional scales (European seas), based on the combination of space and in situ observations, and their assimilation into 3D simulation models: temperature, salinity, currents, ice extent, sea level, primary ecosystems...

What is the link with Duacs?

The Cnes/CLS system Duacs is the backbone of MyOcean's Sea-Level Thematic Assembly Center (SL-TAC). The SL-TAC is a production unit which provides operational European forecasting centers with directly usable, mission-coherent and high-quality sea-level data from all past and present sensors.
In the MyOcean framework, Duacs is expected to provide Near Real time, offline and re-analyzed L3/L4 data to the project, to develop new products or to improve existing ones, but also to demonstrate its operational capability (global MyOcean system description, performance indicators, ...) and usefulness. The demonstration is the step towards a possible long term support from Europe to operational oceanography and the associated ocean observation capacity (e.g.: altimetry satellites).
As far as the end-user is concerned, Duacs will comply with two notable requirements from MyOcean:

• All MyOcean products are distributed free of charge for all applications (scientific or commercial) both offline or in near real time
• All MyOcean users must be identified by the project's user desk in order to map data flows from the original provider to the user and above all to try and improve its service towards them

Until 2009, Duacs data were divided into 2 categories: data older than 30 days (anonymous access, free of charge, all applications allowed), and near real time (<30 days) free of charge for scientific use or even commercial if enough scientific value is added to the product (e.g.: assimilation in a model).
The MyOcean data policy has the following notable impacts for Duacs users:

• The along-track data from Duacs are MyOcean products. Therefore the 30 day restriction to commercial application disappears. Anyone, including commercial applications, can now request an access to Near Real Time along-track data from Duacs (along-track SLA, SLA+ and so on). These data are jointly distributed by the MyOcean project and Aviso.
• The multi-mission maps are not in the MyOcean catalogue, but they are an internal validation dataset for project partners. These data are still available free of charge for scientific use. Commercial and non-scientific users can still get access to Duacs data provided that their request is accepted. These data are still distributed by Aviso.
• Anonymous data repositories will be closed on Aviso. A light-weight identification process is required. Generally speaking barely more than name, email and a couple of classical questions are necessary to subscribe for data access. 
• This data policy is applicable both for near real time and offline or delayed-time data (e.g.: level 3 derived from level 2 OGDR are considered as under the L3 data policy).
• Lastly, for all datasets delivered free of charge, the license requires explicit source credits in publications and science project reports derived from these data.

So in a nutshell: along-track SLA are free for all, maps are free for scientific use, and all products require a license agreement to get your data access setup. Barring the new identification process, this is basically transparent for all of you since a vast majority of Duacs users are either scientific or add a significant value to the original product that will justify unrestricted data access.
Note that the data policy does not take into account the status of the end-user: if a university is involved in a commercial project, its request will be processed like a private company's would be. Similarly if a scientific entity is granted free data access in response to a request for scientific use only, and if it then starts using these data in a profit-oriented project, then it can be considered a breach of license.

Practical consequences for Duacs users

Here are practical consequences:

• First of all, if you're not using the new FTP server (ftp.Aviso.oceanobs.com), you should get in touch with Aviso or MyOcean to get your access set up. The old repositories will be closed in the coming months.
• If you're using along-track data, you should register for free data access to Aviso or MyOcean. You'll have to sign up the license (e.g.: no redistribution unless formerly accepted by the project), and you should be able to access your data (free of charge),
• If you're using maps for science or non-profit projects, you should register for free data access to Aviso. You'll have to sign up a slightly more restrictive license (e.g. :  no commercial use) more or less in line with what was done for NRT data until 2009, and you should be able to access your data (free of charge).
• If you're using maps for commercial use, or if your application is not in line with the standard license agreement (e.g.:  web portal but limited to a small number of purely scientific projects), then you should get in touch with Aviso or CLS who will process your request. The (possible) fee associated to data delivery is discussed on a case by case basis.
• If you're using multiple data sets, you'll have to make multiple requests, and your unique data access will be configured accordingly.

Introduction

Last year started an ambitious reprocessing of all altimetry data since 1992 (cumulated total of about 55 years of 1 Hz data). Our historical altimetry database has been updated to the most recent reprocessed GDR (e.g.: Jason-1 GDR-C from 2009), but also to up-to-date standards (GDR-C or equivalent), on all missions. Duacs-DT itself has been improved here and there (new processing, better transition from TP to Jason, better mapping parameters) and this reprocessing implements all changes introduced in Near Real Time processing.

One should note that this reprocessing was able to benefit from data, algorithms or experience developed various Cnes projects and reprocessing. The synergy with Cal/Val and MSL activities helped with the long-term climate-oriented coherency, and a better handling of reference missions and regional MSL.  The SLOOP project provided a framework for the computation of new Mean Profiles for all missions, and SLOOP will produce better reference surfaces (Mean Sea Surface, and Mean Dynamic Topography) which are used by Duacs for drifting altimetry missions or the computation of Absolute Dynamic Topography.

However due to time or workload constraints, it was not possible to integrate all possible improvements associated to recent projects: Envisat GDR-C reprocessing not yet available, ERS reprocessed data from the REAPER project are not yet available, retracked T/P are still being analyzed, and only a fraction of the coastal improvement from Pistach or Coastalt projects were actually used due to the lack of high-resolution along-track data in Duacs.

The weekly resolution used so far for DT maps was insufficient wherever the time decorrelation scale is close to 15 days, especially when end-users want to perform a simple linear time interpolation between consecutive maps. However, switching to a daily resolution involves the computation of more than 6200 maps (some of them using three or four sensors). Not exactly a trifle. As a release date vs resolution tradeoff, the first batch of DT-2010 maps will be released by spring 2010 with a weekly temporal resolution, and the resolution should be increased to a daily resolution equivalent to the NRT resolution by summer 2010.

Note that the DT-2010 generation falls under the new data policy associated to MyOcean (See MyOcean and change in Duacs data policy). Consequently, it will not be distributed anonymously as older products were. When the new dataset is available on Aviso, you'll have to subscribe to a nominative (or company or lab) data access. As mentioned above, barring the light-weight identification needed, the change should be mostly transparent to all scientific and nonprofit users.

Here are some notable upgrades that the new generation Duacs-DT product will include (not exhaustive):

• T/P : new non parametric Sea State bias solution from N. Tran and S.Labroue with up-to-date standards (e.g.: DAC or wind algorithm) and orbit solution
• T/P : new orbit solution, kindly provided by GSFC
• Jason-1 : GDR-C used from 2009 reprocessing
• Jason-1 : used as a reference mission instead of T/P for 2002-2005
• Jason-2 : all GDR used from the mission beginning
• Jason-2 : used as a reference mission from 2008
• Envisat :  used in place of ERS from cycle 9, except for missing cycle 15 (still using ERS2 for this 35-day period)
• Envisat : new non parametric SSB solution from S.Labroue
• Envisat : GDR-C orbits used (after Cal/Val certification)
• GFO : new orbit solution, kindly provided by GSFC. The new solution not being available during complex periods, the GDR orbit is also used with empirical coherency restoration in between
• GFO : new non parametric Sea State bias solution from N. Tran and S.Labroue with up-to-date standards and orbit solution (computed after orbit error minimization on calibrated reference missions)
• ERS : minimization of brightness temperature drift before wet tropo computation (NN)
• All missions: GDR-C or better standards applied whenever necessary (GOT4v7, High Resolution DAC correction,...)
• All missions: new mean profiles computed in coherency with the new standards and algorithms. New algorithms were applied to correct for time-averaging period discrepancies (e.g.: T/P != Jason-1) or ocean variability. The new mean profiles are still referenced over 1993-1999 for the sake of coherency, but they integrate a precious information from the most recent missions and datasets.
• All missions: minor upgrades of the editing process and complete re-editing based on new standards and corrections.
• All missions: complete re-computation of the empirical cross-calibration and homogenization processes (orbit error reduction using a reference mission, and long wavelength error minimization)
• Reference missions: revisited bias from T/P to Jason-1 and transition from Jason-1 to Jason-2 in order to correct for geographical discrepancies affecting regional MSL studies carried out on Duacs multi-mission maps. Only the inconsistencies which are explained and understood are minimized (update to 2009 knowledge). No geographical minimization is performed between TP-A and TP-B, no waveform leakage correction is applied in this processing (empirical minimization process not fully certified yet).
• Mapping process: updated suboptimal Optimal Interpolation process to minimize transition artefacts (increases map computation time by a factor of 10)
• Mapping process: map coverage extended at high latitudes (previously dismissed due to lack of confidence in Mean Profile)
• Mapping process: time resolution increased (first release still on 1 map per week basis, to be increased to 2 or 7 maps per week by mid-2010).