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TABLE 3. APPROXIMATE ACCURACIES OF IGS
PRODUCTS
GPS ephemerides 5—30cm
GPS clocks 0.5 — 5 nsec
Earth orientation (pole) 0.2 — 0.7 mas
) 0.1- 0.5 ms/day
3 mm —-3cm
Earth orientation (length of day
Station coordinates (annual)
lynx http://igscb.jpl.nasa.gov/
will connect the user to the CBIS. For those with X-
window terminals, xmosaic for Unix systems, or the
equivalent Macintosh or Windows application, allows a
graphical interface to the CBIS.
At the top level of the CBIS one views the following:
The Central Bureau, funded by NASA at
Caltech's Jet Propulsion Laboratory,
supports an Information Service:
* IGS Mail: An archive of exchanges
among IGS participants.
* IGS Reports: An archive of reports
from IGS Data and Analysis Centers.
* Regional Mail: An archive. of
exchanges among those interested in
specific regional GPS networks.
These collections, with other data, are
also available through anonymous FTP.
Categories in bold can be selected for further exploration.
By sending a message to
igscbüigscb.jpl.nasa.gov, you can request that
your Internet e-mail address be added to one or more of
the mail and report distribution lists. The anonymous
FTP category is explained in more detail in Table 4,
where top-level files and directories are given.
BENEFITS TO USERS
The IGS has been in formal operation for over two years,
and detailed analysis strategies that exploit the qualities of
its data and products are still being developed.
High quality Rinex tracking data from the global tracking
network, GPS ephemerides that are more accurate than
the broadcast orbits by at least an order of magnitude, and
precisely-determined coordinates of dozens (and
eventually hundreds or more) of sites distributed over the
entire globe as well as regionally, all provide benefits to
users.
TABLE 4. TOP-LEVEL OF CBIS ANONYMOUS
FTP AREA
files: IGSCB.DIR NEWS.TXT README.TXT
TREE.TXT
center contains information on the various IGS
Centers (Analysis, Data, etc.)
data indicates where — at which Data Centers —
Rinex data reside
general miscellaneous information on GPS, IAG,
and IGS, including the IGS Terms of
Reference
mail contains indices of mail messages, and the
messages themselves
product contains Analysis Center products: precise
ephemerides, earth orientation, weekly
summaries
software contains source code for CBIS-exploring
utilities
station contains information on IGS stations
Investigators who use GPS in local regions can include
data from one or more nearby IGS stations, fix the site
coordinates from such stations to their ITRF values, and
fix GPS satellite positions to their IGS-determined values.
By doing so the investigator can reduce data from his own
network with maximum accuracy and minimum
computational burden. Furthermore, the results will be in
a well-defined global reference frame.
For more information contact
IGS Central Bureau
Jet Propulsion Laboratory 238-540
4800 Oak Grove Drive
Pasadena, CA 91109 USA
voice: 818 354 8330
FAX: 8183936686
e-mail: igscb@igscb. jpl .nasa.gov
ACKNOWLEDGMENTS
The authors would like to thank all participants of the IGS
for their contributions and continued dedication. These
cooperative efforts have enabled the IGS to realize a
successful and productive international operation.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996
