GDAC data stream (for NetCDF Argo files)
For users interested in manipulating the actual Argo NetCDF files, the GDACs should be the route
to access Argo data. Both GDACs offer access to the complete Argo data collection, including
float metadata, detailed trajectory data, profile data and technical data all in NetCDF format.
The data is organized in either a geographic (by ocean basin) or a Data Assembly Centre (DAC)
manner and is provided via HTTP and FTP as well as through data browsers and other portals like
OpenDAP, OGC-WCS, etc. It
is important to understand the
naming system of the files as well as the variable names and quality control flags within each
data file. See the ADMT
Documentation page for the Argo User's Manual and the Argo quality control manual for more
Which GDAC should I use?
This depends on a number of factors but the first issue is location. North American users will
likely use the Monterey site and European users the Coriolis site. Beyond this, the choice is
a matter of which GDAC has a mode of access that best suits the user's needs.
HTTP and FTP Access
The http and ftp sites are identical and are
organized into three main folders: a "dac" folder which sorts the data by Data Assembly Centre
(DAC), a "geo" folder
which sorts the data by ocean basin, and a "latest_data" folder which includes the most recent data.
There are also several index files in the top directory containing a list of metadata on each type
data file (meta, prof, tech and traj) contained in the "dac" and "geo" folders. It is possible to download these lists and search them
for floats in specific regions, times, DACs, etc. There is also a grelist which contains a list of
floats that likely have sensor problems.
Monthly Snapshots via DOI
Each month since the start of 2014, there is a snapshot taken of the GDACs which is assigned a DOI. Users can simply choose the latest month's snapshot of the GDAC and access it via the DOI link making it easy to cite in publications.
via the GDAC synchronization service
The rsync server "vdmzrs.ifremer.fr" server provides a synchronization service between the "dac" directory of
the GDAC with a user mirror. See the
ADMT website for more details. From the user side, the rysnc service:
- Downloads the new files
- Downloads the updated files
- Removes the files that have been removed from the GDAC
- Compresses/uncompresses the files during the transfer
- Preserves the files creation/update dates
- Lists all the files that have been transferred (easy to use for a user side post-processing)
Synchronization of a particular float:
- rsync -avzh --delete vdmzrs.ifremer.fr::argo/coriolis/69001 /home/mydirectory/...
Synchronization of the whole dac directory of Argo GDAC:
- rsync -avzh --delete vdmzrs.ifremer.fr::argo/ /home/mydirectory/...
Both GDACs also provide data selection tools which allow users to enter different search criteria
and then select different ways to display and receive the data. Regardless of the GDAC, users
can search for data using the following means of selecting data:
- By selecting a latitude/longitude and time range
- By DAC (Data Assembly Centre)
- By Delayed Mode or Real Time quality
After providing selection criteria at the
US GDAC Data Browser, one can expect the following:
- A profile location plot for all profiles returned by the query (may be plotted with or
without float ID for queries returning many profiles)
- Download of selected profiles (in netCDFnetCDF Multi-Profile format) as a TAR file
- Plots of T-P and S-P for individual profiles
- Plots of float tracks for individual floats
Image of US GDAC webpage interface
The Coriolis GDAC interface allows one to search by a few additional criteria:
- profile or trajectory file
- measured parameter
- platform type (ie, access to additional non-Argo data (XBT, CTD, drifters, moorings, thermosalinograph,ADCP) is
available from Coriolis through the same interface
The results can be downloaded as either NetCDF or ASCII data and a map is displayed with the locations
of all the resultant floats.
Image of Coriolis webpage interface
Argo float data and metadata are available a variety of web services suchs as OpenDAP, OGC-WCS, etc.
here for more information.