International GPS Service for Geodynamics (IGS), Central Bureau

The International GPS Service for Geodynamics (IGS) supports researchers
who use satellites in the U.S. Defense Department's Global Positioning
System (GPS) for studies in geodynamics. GPS satellites transmit signals
that allow one to determine, with great accuracy, the locations of GPS
receivers. The receivers can be fixed on the Earth, in moving vehicles,
aircraft, or in low-Earth orbiting satellites. The time evolution of
receiver locations allows researchers to study the motions of tectonic
plates, displacements associated with earthquakes, earth orientation, and
other geophysically interesting phenomena. Global Positioning System (GPS)
uses microwave measurements of range (transmitter-to-receiver distance),
accurate to within a centimeter or less, to determine positions of stations
on the Earth's surface. Relative site positions can be measured to within
a centimeter. This system was developed by the U.S. Department of Defense
for military navigation and timing.

The INTERNATIONAL GPS SERVICE FOR GEODYNAMICS (IGS), a service established
by the International Association of Geodesy (IAG), officially started its
activities on January 1, 1994, after a successful pilot phase of more than
one year. IGS is based on about 40 globally distributed permanent GPS
tracking sites, three Global Data Centers, five Operational or Regional
Data Centers, seven Analysis Centers, and a Central Bureau. Some fifty
institutions and organizations contribute to these activities.

IGS routinely provides :
* High-quality orbits for all GPS satellites (estimated accuracy better
than 20 cm)
* Earth Rotation Parameters
* Contributions to the determination of the tracking site coordinates in
the International Terrestrial Reference Frame (ITRF), in cooperation
with the International Earth Rotation Service (IERS)
* Phase and pseudorange observations in daily RINEX files for each IGS
tracking site

The tracking data are available at various Data Centers, the individual
orbits determined by the Analysis Centers at the Global Data Centers,
and the combined official IGS orbits at the Central Bureau and the Global
Data Centers.

To reach the Central Bureau, FTP to sideshow.jpl.nasa.gov, login
anonymous, use your internet address, as password, and change
directory to /igscb.

The IGS Central Bureau Information System (CBIS) is accessible by :
* Internet (anonymous ftp, sideshow.jpl.nasa.gov, directory /igscb)
* World Wide Web (http://igscb.jpl.nasa.gov, using e.g. MOSAIC or LYNX)
* E-mail using an ftp server (infos available at the Central Bureau)

This Information System consists of a collection of ASCII files easily
accessible through anomymous ftp. The file TREE.TXT contains a synopsis
of the directory structure and the files found in the system. There is a
small program available (called "cbis") that facilitates the downloading
and immediate display of files from the Information System (see in the
directories /igscb/software/unix, .../vms, and .../dos). The CBIS contains:
* information about the availability of tracking data and IGS products,
the access to tracking data and IGS products, data file formats, the
IGS data and analysis centers, the IGS tracking stations, the current
status of the Global Positioning System
* IGS orbits, IERS earth rotation parameters
* mail and e-mail addresses
* access software, compress/decompress routines
* IGS Mail: An archive of exchanges among IGS participants.
* IGS Reports: An archive of reports from IGS Data and Analysis Centers.
These collections, with other data, are also available via anonymous FTP.

Please direct questions to the Central Bureau.