The latest version of the Duacs-DT software (v2.0) has been installed and activated on the production servers. It was used for a complete re-analysis of past and present altimetry (from ERS-1 to current missions) with the state-of-the-art corrections, models and references recommended for the next generation of Jason-1 & Envisat GDR, as well as CalVal and cross-calibration algorithms.

The latest version of the Duacs-NRT software (v8.1) has been installed and activated on the production servers. It is now running and all status and reports are nominal. The first NRT data were generated a couple of weeks ago in order to restore the availability of RT data for Envisat as soon as possible (more information).

The new versions of both components add some significant changes in altimetry processing and data availability so you might want to look at the release notes.

Duacs release notes

• Delayed Time (DT) and reanalysis (RAN) component: v2.0
  • New product class: regional products for the Black Sea
  • New data set available: Envisat Side B
  • New data set available: ERS-1 Geodetic phase
  • Data processing improvement: minor costal improvements
  • Data processing improvement: High resolution Dynamic Atmospheric Correction
  • Data processing improvement: New Mean Profiles
  • Upgraded input data (latest GDR version available).

• Near Real Time (NRT) component: v8.1
  • Data processing improvement: High resolution Dynamic Atmospheric Correction
  • Data processing change: GIM ionosphere correction for Envisat
  • Transparent for users: upgrades of controls and QC procedures

Upgrades and upcoming changes on Duacs

• Change in product class: end of the experimental phase on the Real Time data
• New product class: Black Sea regional data in NRT
• Data processing improvement: Costal improvements and impact on Level3 data
• Data processing improvement: towards an orbit error reduction process without a reference mission
• Online status & Key Performance Indicators
• Format upgrades & standards

The latest version of the Ssalto/Duacs software (v8.0) has been installed and activated on the production server.
New features in this version include:

• New demonstration product : integration of "real time" (not NRT) altimeter data in Duacs.
  As shown during the latest OSTST meeting, timeliness is a critical element in the accuracy of (near) real time systems such as Duacs, especially now that missions are aging and that the amount of usable NRT data is decreasing quickly. So far we were unable to process real time data flows properly due to the poor quality of the RT orbit determination or due to inconsistent ground processing designs. Yet a lot of work has been put on the integration of real time data sets in Duacs processing. (more information)
• In addition to the classical NetCDF formats, Duacs-NRT is now generating a more newcomer friendly product based on the Google Earth format. This demonstration product combines high resolution maps and along-track satellite coverage with display toggles for each daily data set. Thanks to the powerful and user-friendly interface provided by Google Earth, Duacs users now have a quick-look product if they need to know where the combined map is based on actual along-track measurements or optimally interpolated in space and time from nearby data. The latest public map (older than 30 days) is available here
• Knowing where and when they will get future along-track data is very important for some regional or local applications : to monitor fronts and eddies, to schedule in-situ measurements colocalised with future altimeter data, to predict local data shortage for assimilation... To fulfill this need, Duacs is now providing an estimation of the along-track data coverage expected in the next 7 days. This information is given in a standard SLA format or as a GoogleEarth quick view (see above). If your laboratory has a private access to recent NRT data (<30 days not anonymously distributed, see Duacs handbook), then you can access them here: ftp://ftp.cls.fr/pub/oceano/ your directory /res/expected/ <mission> </mission>
• Improvements to the Near Real Time quality control (QC) report. This small PDF document is a raw compilation of the most relevant figures analysed twice a week by the Duacs quality assessment team. Duacs users can download the latest reports from this FTP directory:
• Minor upgrades in various processing steps (notably), as recommended by the Cal/Val team and the altimetry community.
• Various software improvements to increase the robustness of the NRT component, the availability of NRT products, and the warnings and controls given to Duacs operators.

The latest version of the Ssalto/Duacs software (v7.1) has been installed and activated on the production server.
New features in this version include:

• There is an historical bias between DT and NRT data sets (about 2cm) since the T/P to Jason NRT transition performed in 2002. This bias will be smoothed out with a 3 months ramp.
• USO correction for Envisat is now included.
• Geostrophic velocity algorithms are improved.
• MFStep results are now integrated in Duacs reports.

The latest version of the Ssalto/Duacs software (v7.0) has been installed and activated on the production server. New features in this version include:

- A drastic change in the product delivery frequency in Near Real Time. User feedback proved that data timeliness was critical for some applications. Duacs has been significantly upgraded to meet these user needs. The complete product generation (along-track data, maps, global and regional products...) will be performed on a "daily" basis to multiply by 3 the production frequency (better data timeliness) and to smooth the planning of operational users.

- So far, the access to regional products on the Mediterranean Sea (formerly known as MFStep products) was restricted in NRT to scientific uses and delivered only upon request to the Aviso team. With Duacs v7.0, all Mediterranean specific archives older than 30 days will be distributed publicly with an anonymous FTP access.

- The old binary format for along-track SLA products will be *discontinued*. This historical format is no longer supported by Duacs since early 2005.

- The historical PF product class will be discontinued. Hardly used and somewhat redundant with the standard OER class, it will be pruned in an effort to clarify and to simplify the Aviso catalogue.

The latest version of the Ssalto/Duacs software (v6.1) has been installed and activated on the production server. The first NRT data to be produced with this new software will be delivered on the AVISO ftp site starting from March 24, 2006.
New features in this version include:

Near Real Time component

• A new Mean Dynamic Topography (MDT). The MDT used so far to build absolute products was Rio03. Duacs will now use the latest MDT using GRACE data (Rio05) to improve Duacs absolute products. To prevent potential discrepancies between old and new products, a complete reanalysis of existing absolute data sets has been carried out. All absolute Duacs data on AVISO (NRT and 13 years of DT, along track and gridded, topography and currents, ftp and OpenDAP/LAS) will be updated in the coming days to ensure the series' continuity. Note that regional products on the Mediterranean Sea (formerly known as MFStep products) are still based on the Med-specific MDT from Marie Helene Rio.
• Slight modifications to the Near Real Time quality control (QC) report. This small PDF document is a raw compilation of the most relevant figures analyzed twice a week by the Duacs quality assessment team. Duacs users can download the latest reports from this FTP directory
• Minor upgrades in various processing steps (notably editing), as recommended by the Cal/Val team
• Various software improvements to increase the robustness of the NRT component, the availability of NRT products, and the warnings and controls given to Duacs operators

Delayed Time component, processing and products

• Duacs has recently performed a complete re-analysis of all altimeter data (from ERS1 to current missions) with the state-of-the-art corrections, models and references recommended for the new generation of Jason/Envisat GDRs, as well as the best Cal/Val and crosscalibration algorithms.
  The quality assessment and feedback from end-users show a significant improvement on the previous generation of Duacs maps that was based on y2000 standards and only two satellites. Merging more missions with better processing significantly improved the comparison of altimeter and in-situ data
• The DT series will be updated in the coming days (from June 2005 to late October 2005). The latest update was particularly tricky as it spans over the demise of T/P which was the reference of the Orbit Error Reduction process (multi-mission crossover reduction). Duacs had to switch to a Jason-based reference while ensuring a seamless transition, despite minor discrepancies observable on GDR data sets (see recent results from the Venice Symposium & OSTST).
  This delicate transition being tackled, the DT production should be performed every month (as opposed to 4/6 months so far) provided that Duacs receive GDR data sets from all missions.

The latest version of the Ssalto/Duacs software (v6.0) has been installed and activated on the production server.
New features in this version include:

• New regional products. Initially developed for the MERSEA project, these along track products are specifically developed for regional applications. They will be delivered on a daily basis. The nomenclature, content and processing used for these regional SLA are detailed in the AVISO handbooks
• Operational use of the state of the art altimetry corrections that will be used for the second generation of Jason/ Envisat GDRs.

These corrections have been recommended in the latest OSTST meetings and you can find information about these evolutions on the OSTST reports/ posters.
This is an important evolution. It will notably increase the quality of Duacs products. However the new corrections potentially create a slight discontinuity with past products. As per usual, we have tried to minimize these effects. The most notable changes come from:

• Operational corrections of high frequency signals. This correction is based on Mog2D, the barotropic model developed by LEGOS (Carrere & Lyard 2003).
• GIM-based ionosphere correction for GFO. This correction replaces old ionosphere models. It is based on the NRT TEC grids produced by JPL. The GIM correction will be used as a reference for the NRT validation and monitoring of the dual frequency iono correction of other missions.
• Various software improvements to increase the robustness of the NRT system, the availability of the NRT products, and the full compatibility with the next generation of IGDR products for Envisat and Jason.
• Enhanced quality reports (daily, production, long term monitoring of NRT data) to check and to ensure the current quality standard of the SLA/MSLA products of Ssalto/Duacs.

The latest version of the Ssalto/Duacs software (v5.4) has been installed and activated on the production server.
New features in this version include:

• Distribution of a quality assessment report to monitor the quality of NRT altimeter data. This raw PDF document is a small compilation of the most relevant figures analyzed twice a week by the Duacs quality assessment team: input data delay, missing data, edited/valid data, crossover statistics, pass by pass statistics... It is provided 'as is' on a best effort basis, without documentation/tutorial nor user support. Duacs users can download the latest reports from FTP
• 0.25° Ascii grids, which are no longer supported since early 2004, will no longer be distributed. However a NetCDF version of this product will be produced.
• The ADT (Absolute Dynamic Topography) products distributed so far were only available for the global data set. As of this version, the ADT-class will be added to the Mediterranean sea products (aka: MFStep products). They are generated using the Mediterranean MDT (Mean Dymanic Topography) by Rio et al, and the Mediterranean-specific MSLA.
• The geostrophic velocity processing will be improved in the equatorial band following the method proposed by Lagerloef et al. Past NRT velocity maps from Duacs may be reprocessed in a near future to ensure homogeneity in the equatorial band.
• Drastic improvements have been implemented in the LWE (Large Wavelength Error) reduction software used by Duacs to ensure a good consistency between various passes/missions for the along-track SLA/ADT. Improvements are notable in regional or coastal areas, and on semi-closed and closed seas, or wherever the LWE signal is strong.
• Along-track SLA/ADT products are now distributed in a second format (NetCDF). The storage convention used allows data I/O which are more flexible and more accurate, especially regarding measurement dates. Users are strongly encouraged to consider this format. The historical binary format will be maintained until December 2005. However, it will no longer be supported by the Duacs user service.

Version 5.0 of the Ssalto/Duacs software includes:

• New Absolute Dynamic Topography ("ADT") products.
  By using the 7-year Mean Dynamic Topography developed as part of the Enact and Mercator projects [Rio, 2003] (see Ocean Currents, Image of the Month for February 2003), along with the regular (M)SLA products, Ssalto/Duacs can now generate along-track and gridded ADT as well as absolute geostrophic velocities. More information regarding these new products (nomenclature, directory, format...) will be available next week on our website and in the user handbook.
• T/P back in the system as a fourth mission processed in NRT, on its new orbit (see Flying tandemhttp://jason-interne.cls.fr/html/mod_actu/module/affiche_actualite.php3?idActualite=259&langue=en). Note that all T/P data processed by Duacs are obtained using an accurate mean profile that is fully compatible with existing means for Jason-1, Envisat and GFO. More information regarding T/P (tandem) SLA shall be found in [Le Traon, Dibarboure, 2003, submitted to Marine Geodesy Jason 1 Special Issue]
• New mean profile for GFO. The 'old' mean profile computed using Geosat data [see Hernandez et al, 2000] has been replaced by a new mean track computed using only GFO GDR data provided by Noaa. This new mean track will enhance the accuracy of GFO SLA significantly.
• Update of the geophysical and intrumental corrections used. Note that, as of Duacs v5, the electromagnetic bias used for Jason, T/P and GFO will be replaced by the latest non-parametric bias estimated by S.Labroue in 2003 (see SWT Presentations 2003 or 2002 or Cnes & Noaa reports for more information). At the same time, offsets will be applied so as to remove discontinuities in all user data.
• Enhancement of the mapping software to better take into account coasts & islands. This new "line of sight" feature will now prevent an altimeter measurement on one side of a coast or island (for instance in the Gulf of Mexico) to be taken into account in the computation of a grid point on the other side (for instance in the Pacific ocean). This new feature should improve the quality of Duacs products in the vicinity of any complex coastlines. Generally speaking, it is still important to remind that altimetry is not to be taken for granted in such coastal areas were measurement and correction errors are important.
• Various software improvements to increase the robustness of the NRT system, and the availability of the NRT products.
• Enhanced quality reports (daily, production, and long term monitoring of NRT data) to check and to ensure the current quality standard of the SLA/MSLA products of Ssalto/Duacs.

Envisat data are now processed, and replace ERS-2's
Since June 22, ERS-2 onboard tape recorder used for the altimeter data have had failures. This means that altimeter data are unavailable except within the visibility of ESA ground stations over Europe, North Atlantic, the Arctic and western North America. Its was thus decided in July to stop processed ERS-2 data, and replace them with Envisat's.

Gridded Ssalto/Duacs data (NRT-SLA and geostrophic currents) older than one month are available via a Live Access Server. You can thus draw your own map and retreive the data

• Data will be delivered twice a week from now (Wednesday and Saturday). Data are processed as before (from the same amount of measurements). There will not have any change in the file label and in data format, and the files will remain in the same directories.
• Data older than one month are available freely on an anonymous ftp. Data of less than one month stay in the same directories than before.

Jason-1 takes over Topex/Poseidon.

• The new version of the system has several improvements compared to the version that has been running since 1998: Sea level anomalies (SLA) will be now provided relative to a 7-year mean (1993-1999 from Topex/Poseidon and ERS data) compared to a 3-year mean for the previous system. This will yield large differences due to interannual variability as can be seen on the figure below.
  For the assimilation systems, the best would thus be to use a new mean (1993-1999). Another possibility would be to add to your existing 3-year mean (1993-1995) the differences between the two means (as shown on the figure) that we can also provide as a numerical file. This will give you a mean compatible with our SLA data and will minimize the difference between the old and new systems.
• Improved geophysical corrections are used to correct altimeter data : new tidal model (GOT99) and an improved inverse barometer correction using a variable time mean pressure.
   
• Improved processing algorithms for orbit error reduction and mapping. They use, in particular, an improved statistical description (covariance) of noise and ocean signal.
   
• Geosat Follow On data are now included in the routine processing [Le Traon et al.: Can we merge Geosat Follow On with Topex/Poseidon and ERS-2 for an improved description of the ocean circulation ?, submitted to Geophys. Res. Letters]
   
• New formats are now used for the maps (NetCDF) and we are now using a 1/3° grid in a Mercator projection (user handbook - pdf); the maps have the same resolution (in km) in x and y directions (e.g. 37 km at the equator and 18.5 km at 60°N/S). We will continue to provide you for a while with maps in Ascii format on the 1/4°x1/4° grid but this service will not be maintained. The format for the SLA files will not be modified.
   
• Names of files both for SLA and MSLA will change (more information in the user handbook - pdf).