Getting NVSS data products by anonymous FTP

As an alternative to using a Web browser, the principal NVSS data products can be obtained from this MIRROR archive by freestanding anonymous FTP:

      ftp ftp.mrao.cam.ac.uk
      (login as anonymous, with your e-mail address as password)
      cd nrao/nvss          (this directory includes the relevant
                             documentation files and subdirectories)
      ls                    (to list these)
      binary                (if transferring FITS or gzipped data)

The files you can see in this directory (nrao/nvss/) are:

      paper.ps and paper.ps.gz  (uncompressed and compressed postscript
                                 versions of the main survey paper)
      catalog.ps, catalog.ps.gz (uncompressed and compressed postscript
                                 descriptions of the catalog)
      bmdone.eps                (postscript plot of layout of 4x4 deg
                                 images, showing which are available)
      

The subdirectories visible at this level are:

      holes.plots/   containing postscript plot files which summarize
                     where there are still gaps within available images.

      MAPS/          containing all the images (see notes below).

      UVDATA/        containing UV data (see notes below).

      CATALOG/       containing the raw source catalog CATALOG.FIT
                     and the NVSSlist software needed to access and
                     interpret it (apply corrections etc). Note that
                     CATALOG.FIT is about 140Mb, so you will need to
                     schedule ftp for a specified overnight time slot
                     to avoid interruption of your transfer by timeouts.
                     Ask you system manager how to set this up and
                     remember to invoke binary mode! Check your messages
                     afterwards to verify transfer was successful. The 
                     catalog and, more frequently, the software are both 
                     subject to evolution, so check the currency of the
                     copies in use at your site from time to time.
                     The files gpaper.ps, gpaper.ps.gz are uncompressed
                     and compressed postscript versions of the paper
                     'Errors in Gaussian Fits' (J.J.Condon, 1997
                     PASP, 109, 166), which gives the derivation of the
                     errors and corrections used in the NVSSlist program.

The large (4 deg X 4 deg) maps and their associated multisource (u,v) data sets are stored as binary files in FITS format. Maps are stored in gzip compressed form. Each map is named by the J2000 right ascension and declination of its center, and the first letter specifies the polarization plane(s). For example, C2230P84.gz is the map cube with Stokes I, Q, and U planes centered on right ascension = 22h 30m, declination = +84 deg. I0224M32.gz contains only the total-intensity plane centered on right ascension 02h 24m, declination -32 deg. The corresponding multisource (u,v) data file is called J0224-32.MS. The compressed map cubes are about 1.7 megabytes in size, and the total-intensity maps are smaller (about 0.7 megabytes) for faster access by users not interested in linear polarization. A postscript plot shows the maps currently available. The postscript file paper.ps (about 4.7 megabytes) contains a detailed description of the NVSS.

A sample anonymous FTP session is shown below:

     ftp ftp.mrao.cam.ac.uk
     login: anonymous
     password:             (type your full email address here)
     cd nrao/nvss          (to access the NVSS public directory)
     ls                    (to list the directory contents)
     get paper.ps          (to get a postscript copy of the paper)
     binary                (to copy binary files)
     cd MAPS               (to access the MAPS directory)
     get C2230P84.gz       (to get the compressed map cube centered 
                            on 22h 30m, +84 deg)
     get I0224M32.gz       (to get the total-intensity map centered
                            on 02h 24m, -32 deg in compressed form)
     cd ../CATALOG         (to go to the CATALOG directory)
                           If you wish to transfer CATALOG.FIT, the FITS
                           binary table containing the source catalog
                           (140Mb), you will need to schedule an overnight
                           ftp for a specified (quiet) time slot to
                           avoid timeouts and check your messages to
                           verify that a successful transfer was
                           achieved. (Ask your system manager how to
                           set up the job).
     quit

Compression: The images are stored as standard FITS files compressed in GNU zip (gzip) format, the .gz extension denoting this compression. Gzipped files may be uncompressed with the command gunzip which is available for most computer systems. See the text file nrao/nvss/compress.txt for a more detailed description of gzip.

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