CEDA Archive Web Download Service

Access the Download Service here:   http://data.ceda.ac.uk/

This service allows you to access the data held in the CEDA Archive:

  • browse the archive directory structure
  • log into myCEDA service for access to restricted datasets
  • download single and multiple files
  • view and subset NetCDF file contents
  • see in-browser plotting of NASA-Ames files

Additionally, the  OPeNDAP technology underpinning this service allows additional functionality such as accessing file contents directly via the internet from within data processing scripts written within Python, Matlab IDL and other scripting languages. 

Viewing and downloading individual files

  • Text files - You may find that some text based files will automatically open in your web browser when selected. You can then download these files by using the Save as... facility on your browser (usually found under the File drop-down menu). Others will start to download directly.
  • Binary and Compressed files - these should automatically start to download to your computer. WinZip on Windows or gzip and tar utilities on Linux machine may be needed to unpack the contents.

Download multiple files

You can use the Download multiple files option at the top of the file listing to bundle together several files and download them all in one go. This can be more efficient for handling several small files but should not be used for many large files (e.g. amounting to more than 2-3Gb in total - e.g. a few large files or many (100+) small files), as resources used in creating the zip file on-the-fly can cause performance issues for other users.

Note that attempting to download many files at once is likely to result in long download times and possible failure.

Non-JAMSIN users may avoid this issue is to download via the CEDA archive FTP service, or to split large downloads into more manageable chunks. 

JASMIN USERS: Remember also that if you are doing your data analysis on JASMIN, you do not normally need to download the data as the CEDA archive data is available as a read-only file system. 

Downloading multiple files from a single directory

Use the data browser to navigate to the directory that you want to download files from then enter an appropriate file specification in the 'Download multiple files' box. You can use the following special characters, i.e. wildcards, in the file specification (wildcards may be used within file names, directory names or both together):

* Wildcard which matches zero or more characters.

Examples:

  • * matches all files in the directory.
  • wt* matches all files beginning with "wt".
  • *.dat matches all files ending with ".dat"
  • wt*.dat matches all files beginning with "wt" and ending with ".dat"
? Wildcard which matches exactly one character.

Example:

  • as9?0102.dat matches "as990102.dat", "as980102.dat", "as970102.dat" etc.
[ ] Character list wildcard within square brackets which matches exactly one character. Multiple characters and range expressions may be mixed within each list wildcard.

Example:

  • 199[69].dat matches 1996.dat and 1999.dat
  • 200[0-5].dat matches 2000.dat, 2001.dat, etc through 2005.dat
  • 200[0-379].* matches all files 2000.*, 2001.*, 2002.*, 2003.*, 2007.*, 2009.*
  • 1993/????0[1-6]/*.2bt matches all files 1993/*/*.2bt for the first six months of 1993.

Downloading multiple files from multiple directories

If you want to download files from more than one directory then you can use the 'depth' parameter. By default this is set to 1, which selects only files from the current directory. Specifying a depth of 2 will select files from the current directory and from any sub-directories below the current directory. Specifying a depth of 3 will select also select files in the sub-directories of sub-directories. Currently you can only specify a maximum depth of 3.

Downloading multiple files from selected directories

Using a file specification together with the 'depth' parameter should cover most requirements. However, if you need more control over what directories are selected then there is a more advanced way of doing this. If the file specification includes a / character then it is interpreted as specifying the filename  and path of the files required. For example, the following file specification will select all files ending in '.txt' in the sub-directories with names beginning with 'eae-9':

*eae-9*/*.txt

Note that the 'depth' parameter is still used and you will therefore need to make sure that it is set to an appropriate value. (If you used the default value of 1 then no files would be selected by the above specification as they are all below the current directory).

Plotting NASA-Ames files

NASA-Amesformat files with File Format Index (FFI) 1001 can be plotted from the data browser. Any files which are plottable will have a 'plot' link next to them. Following this link will open a new window showing a plot of the first dependent variable against the independent variable (which in most cases should be time). Below the plot is a form which allows you to select another dependent variable to plot. You can also change the scales of the plot and change the plot symbol. The box labelled  Omit points with value allows you to exclude any points from the plot which have a specified value. This can be used to remove any points which are marked with a special value. (Note that the NASA-Ames format itself requires that a 'fill' value is specified for each variable. These values are automatically excluded from the plot).

Once you have made your selection, press the 'Plot' button on the bottom right hand side of the form to generate the plot.

Scripted Interaction with archive via OPeNDAP

OPeNDAP stands for " Open-source Project for a Network Data Access Protocol", and is a data transport architecture and protocol widely used by earth scientists. There are a variety of libraries available to interact with OPeNDAP services. The following are a few example sites detailing libraries for common languages used within the CEDA data community.

python http://www.pydap.org/
matlab https://www.opendap.org/index.php/deprecated-software/matlab-loaddap
IDL https://www.opendap.org/index.php/deprecated-software/IDLClient

Whist some of these tools may work for public datasets held in the CEDA Archives, users wishing to use data available to registered CEDA users will need to follow additional steps to use security certificates as detailed on the CEDA OPeNDAP:  Scripted interactions help page.

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