[IGS-DCWG-2] IGS Data Center Working Group and GSAC

[Carey Noll]

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IGS-DCWG Mail      13 Aug 10:14:09 PDT 2002      Message Number 2
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Author: Carey Noll

Dear Colleagues,

   It has been several weeks since my last message, introducing the new
working group mailer Angie set up at the IGS CB, as well as asking for 
thoughts on how to start some of our activities.  Unfortunately, I did
not hear from anyone yet, much to my chagrin (I realize the summer is of
course a time of vacations).  Regardless, I would like to draw your 
attention to some recent developments with the GSAC, the GPS Seamless
Archive Center activity.  You may recall Micheal Scharber gave a presentation
at the IGS workshop in April on GSAC.  The GSAC working group recently held
a meeting in Boulder (see the minutes at
http://www.unavco.ucar.edu/data_support/data/gsac/gsac_meeting_boulder-jul02.html
to review progress and make plans for future development. 
At this time the working group would very much like to encourage participation
in GSAC by other GPS archives, particularly outside the U.S.  To that end,
I would encourage you to check out the GSAC web page and supporting 
documents at http://gsac.ucsd.edu, the standards documentation at
http://www.unavco.ucar.edu/data_support/data/gsac/GSAC-1.1.html.
You can test the Retailer client through these web sites.  The web version
provides a useful search tool but has less flexibility and cannot actually
retrieve data.  To use the command-line client, you can download one of
the executables through http://gsac.ucsd.edu/downloads.html.  Bob King and
Michael Scharber note that there are two important limitations of the
current Retailer:
   
   1) The database queries are not yet efficient enough to do a spatial
      (bounding box) search over a time span of more than a month.

   2) There is no mechanism to separate file listings for continuous and
      non-continuous stations, so the return stream for any search spanning
      more than a few days will be very long and dominated by the listings 
      for continuous stations.

SOPAC is addressing both of these problems.  In the meantime, a reasonable
approach is to do spatial search on the Monument Catalog only, and then
then a time-span search on selected sites. The GSAC listings are essentially
complete for western North America, so an instructive direct search
(spatail plus time), might be 

   gsac-client -f info -v -sy 1992 -sd 001 -ey 1992 -ed 180 -t rinex_obs -bb 240,34,241,35

or the equivalent inquiry via the web page.   This query should execute in 
less than 30 seconds.  Please correspond with Michael Scharber
(mscharber at josh.ucsd.edu) with any feedback or questions on the client.  At
this time, the CDDIS is serving as a GSAC Wholesaler; it did not take us a
great deal of effort to implement s/w to create the appropriate supporting
files required by the GSAC infrastructure.  I would encourage all IGS data
centers to consider making the metadata from their archives accessible through
the GSAC.

    I am also hoping to hear from the members of our group as to your
thoughts on a user survey and documenting the data flow of the IGS network.

Regards,
Carey.

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Ms. Carey Noll  Manager, Crustal Dynamics Data Information System (CDDIS)
                                           Secretary, ILRS Central Bureau
Code 920.1                             E-mail:  noll at cddisa.gsfc.nasa.gov
NASA GSFC                                           Voice: (301) 614-6542
Greenbelt, MD 20771                                   Fax: (301) 614-5970
USA                  WWW:  http://cddisa.gsfc.nasa.gov/cddis_welcome.html
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