INTERNATIONAL SERVICES:
“THE INTERNATIONAL GPS SERVICE (IGS)”
R. Neilan
IGS Mission:
‘…to provide the highest quality data and
products as the standard for global navigation satellite systems (GNSS) in
support of Earth science research, multi-disciplinary applications and
education…’
Abstract
The International GPS Service (IGS)
is an approved service of the International Association of Geodesy (IAG) since
1994 and of the Federation of Geophysical and Data Analysis Services (FAGS)
since 1996. The primary objective of the IGS is to provide a service to
support, through GPS data products, geodetic and geophysical research
activities. This report will briefly chronicle the past four years of history
of the IGS. (See the IAG Travaux series under IAG website Publications listing
for previous reports: http://www.gfy.ku.dk/%7Eiag/
Description of the IGS
IGS is based ON over 350 globally distributed
permanent GPS tracking sites, three Global Data Centers, many Operational or
Regional Data Centers, eight Analysis Centers, an Analysis Center Coordinator,
an IGS Reference Frame Coordinator, Network Coordinator, Clock Products
Coordinator, and a Central Bureau. The IGS also includes projects dependent on
the infrastructure afforded by the IGS. Working groups have been established to
focus on the IGS Reference Frame, Troposphere, Ionosphere, and Real-time
applications, and data center issues; projects include: Low Earth Orbiters, the
International GLONASS Service Pilot Project and TIGA Project for Sea Level
studies. An International Governing Board provides policy decisions and
directives that guide the development and operations of the IGS (Table 1).
Over 200 institutions and
organizations in more than 80 countries contribute to these activities! http://igscb/organization/contorgs.html
The
IGS routinely provides various products (Table 2) generated by the IGS Analysis
Centers (Table 3):
- High-quality orbits for all GPS satellites (estimated
accuracy better than 5 cm), and predicted orbits (~25cm)
- Satellite and station clocks
- Earth Rotation Parameters
- Determination of the tracking site coordinates and
velocities in the International Terrestrial Reference Frame (ITRF), in
cooperation with the International Earth Rotation Service (IERS)
- Phase and pseudorange observations in daily &/or
hourly RINEX files for each IGS tracking site
The tracking data are available at
various Data Centers and the combined official IGS orbits and products are
available at the Central Bureau and the Global Data Centers. The combined
official IGS orbits are produced by the Analysis Center Coordinator located
beginning 2003 at the GeoForschungsZentrum Potsdam, Germany.
The Central Bureau is responsible
for the day-to-day management of the IGS and is funded by the National
Aeronautics and Space Administration (NASA) and located at the Jet Propulsion
Laboratory in Pasadena, California. The Bureau maintains an IGS Information
System (CBIS) accessible at: http://igscb.jpl.nasa.gov/
Key developments of the IGS
2000-2003
These reports are generated mid-year
for the IUGG meetings, therefore, a few words on the closing of 1999 is in
order. The IGS supported the International Symposium GPS ‘99 held in October in
Tsukuba, Japan, which drew nearly 400 participants. IGS conducted a four-hour
tutorial planned especially for this symposium that described all aspects of
the IGS. At the IGS Board meeting in December of 1999 it was decided to prepare
a Call for Participation (CfP) for an IGS Low Earth Orbiter (LEO) Project. This
is seen as a new and interesting direction for the IGS, to investigate and
evaluate LEO precise orbit determination with on-board GPS receivers and what
effect this may have on the IGS products, as well as what service this might be
for LEO missions. The Board also approved the creation of a Strategic Planning
Group to develop a five-year plan for the IGS. Number of stations in IGS
network end of 1999: 229.
2000
Y2K passed quietly for the world and
for the IGS network, data and analysis systems. The Strategic Planning Group
met a number of times in preparation for a three-day Board retreat that was
held in December 2000. A Call for Participation in the LEO project was issued
and nearly 30 organizations responded. IGS Reference frame products were
generated for the first time. A meeting in Nice during the EGS was held to
discuss initiation of an envisioned long-term project to implement a
continental reference system for Africa, termed AFREF. Subsequently, the AFREF
Mail service was established by IGS Central Bureau. IGS tutorials and outreach
were conducted in Cape Town and Harteebeesthoek South Africa. Selective
Availability was removed from the GPS system satellites on May 2. A highly
successful and enjoyable IGS Network Workshop was held in Oslo Norway in July
hosted by the Norwegian Mapping Authority. In September, the US Naval
Observatory hosted an IGS Analysis Center Workshop devoted to the time and
frequency joint project of the BIPM and IGS. The successful launch of CHAMP,
which carries on-board high-quality GPS receivers, was met with enthusiasm by
the IGS community and particularly the LEO project participants. SAC-C, an
Argentine Space Agency LEO launched in November providing additional GPS flight
data. During November, IGS initiated the ‘Ultra-rapid Products’ making precise
orbits and predictions available on a sub-daily schedule. Number of stations in
IGS network: 248.
2001
Prof. R. Weber succeeded Prof. T.
Springer as IGS Analysis Center Coordinator miraculously fulfilling the
University of Bern’s commitment to this task through 2002. In February,
GeoForschungsZentrum organized a LEO Workshop in Potsdam, Germany, which was
co-hosted by the IGS. This was well attended and provided a venue to dsicuss
the end-to-end aspects of LEO missions, particularly CHAMP, and their
applications which include POD, gravity, atmospheric oocultation, ionospheric
tomography. Following the workshop, the first meeting of the IGS Real-time
Working Group was held in Potsdam to develop the charter and technical approach
to build a real-time IGS sub-network and related processes. Discussions were
held in Capetown, South Africa with Surveying and Mapping representatives from
most of the southern African nations to discuss and plan a regional realization
of AFREF. This was coordinated by South African Surveying and Mapping Director
of Survey Services, Richard Wonnacott and took place in conjunction with the
CONSAS 2001. The IGS supported a campaign of the Ionospheric Working Group to
collect and analyze high-rate data during the period of the total eclipse of
the Sun during April. A new project called TIGA led by GFZ was established
within the IGS to use GPS observations at tide gauge bench-mark stations in
order to assess long-term sea level change. GPS observations will be used to
remove the signals from coastal crustal deformation or subsidence from the
long-term records. The TIGA has very challenging vertical measurement
requirements that will span decades. The project has facilitated analyzing data
from stations with high latency data availability – some collected only once
per year from remote locations with no access to the internet. This year the
IGS published workshop proceedings in conjunction with outside publishing
companies: GPS Solutions published the proceedings from the 2000 Analysis
Center Workshop; and Physics and Chemistry of the Earth published the IGS
Network Workshop proceedings joint with ‘Towards Operational Meteorology’, the
European COST 716 Action "Exploitation of Ground-Based GPS for Climate and
Numerical Weather Prediction Applications". (See IGS Website for
publication information.) Number of stations in IGS network: 287 stations.
2002
The IGS Strategic Plan 2002-2007 was
finalized, published and distributed. The Natural Resources of Canada organized
and hosted a full workshop of the IGS titled ‘Towards Real-Time’. This was the
first workshop in many years that brought all components of the IGS together
and it was agreed that this was an excellent workshop. Proceedings of this
Ottawa workshop are available at the IGS website. A workshop to discuss the
status of the Ionosphere Working Group was held in January at ESA/ESOC in
Darmstadt. The LEO twin satellites IGS became a member of a United Nations
Action Team on Global Navigation Satellite Systems (GNSS). This Team focuses on
the use of GNSS especially in developing countries, and is chartered by the UN Office
of Outer Space Affairs to address various GNSS related issues. Recommendations
and the Team’s report will be submitted to the Committee on the Peaceful Uses
of Outer Space (COPUOS) in preparation of the next meeting of UNISPACE in 2004.
IGS assisted in the organization of the UN Regional GNSS Workshop in Lusaka,
Zambia in July and met there with a number of responsible people from many
African nations to further discuss and plan the establishment of a continental
reference system for Africa (AFREF). The LEO mission GRACE launched
successfully promising additional data for the LEO Working Group. At the
December Governing Board meeting, Prof. Christoph Reigber of GFZ Potsdam
completed his term as Chair of the Board and was succeeded by Prof. John Dow of
ESA/ESOC. Prof. Gerd Gendt, GFZ, succeeded Prof. Robert Weber, AIUB and
Technical University of Vienna, as the Analysis Center Coordinator. A GNSS
Working Group is set up with plans to position the IGS to take advantage of the
future Galileo and modernized GPS. Due to increasing demands on the data and
product access, a Data Center Working Group was approved earlier this year. IGS
timescale activities moved from USNO to Naval Research Lab. Number of stations
in IGS network: 348 Stations.
2003
The key activities of the IGS this
year are implementation of the IGS Strategic Plan and preparations to celebrate
the 10th Anniversary of the IGS at a Symposium in Bern in March
2004.
Key elements of the IGS strategic
plan 2002-2007
Mission
The
International GPS Service is committed to providing the highest quality data
and products as the standard for global navigation satellite systems (GNSS) in
support of Earth science research, multidisciplinary applications, and
education. These activities aim to advance scientific understanding of the
Earth system components and their interactions, as well as to facilitate other
applications benefiting society.
Long-Term
Goals and Objectives
- Provide the
highest quality, reliable GNSS data and products, openly and readily available
to all user communities.
- Promote
universal acceptance of IGS products and conventions as the world
standard.
- Continuously
innovate by attracting leading-edge expertise and pursuing challenging
projects and ideas.
- Seek and
implement new growth opportunities while responding to changing user
needs.
- Sustain and
nurture the IGS culture of collegiality, openness, inclusiveness, and
cooperation.
- Maintain a
voluntary organization with effective leadership, governance, and
management.
Strategies
of the IGS
To
achieve the long-term goals and objectives of the IGS, three key strategies are
identified:
- Strategy 1:
Ensure delivery of “world-standard” GPS (and other GNSS) data and products, providing the standards and
specifications globally.
- Strategy 2:
Pursue new opportunities for growth to improve the services and serve a
broader range of users.
- Strategy 3: Continuously improve the effectiveness of
the IGS organization
Figure 1. Station locations of the IGS Tracking Network, late 2002.
The
full text of the IGS Strategic Plan can be found at: http://igscb/overview/pubs.html or ftp://igscb.jpl.nasa.gov/igscb/resource/pubs/IGS_sp.pdf
This
document contains more details on the plan, a sgood historical summary of the
IGS, a description of each component and a listing of all participating
organizations. A copy can be obtained by contacting the Central Bureau.
Links to IGS Organizations:
http://igscb/organization/centers.html
Listing of the 127 IGS Associate
members
http://igscb/organization/assocmem.html
IGS Publications:
http://igscb/overview/pubs.html
Acknowledgments
The contributions of the
participating agencies worldwide have made the IGS an incredibly successful
organization. Coordination of this report was performed by the IGS Central
Bureau located at the Jet Propulsion Laboratory, California Institute of
Technology and sponsored by the National Aeronautics and Space Administration.
Table 1. The IGS Governing Board
Members and Former Members, terms as noted. Terms begin on
January 1 of the stated year and conclude on December 31 of the stated year.
Terms of office are generally 4 years for the elected members, and two years
for working group or project chairs.
|
GB MEMBER 2002 |
INSITITUTION & COUNTRY |
FUNCTIONS |
TERM |
|
|
Christoph Reigber |
GeoForschungsZentrum Potsdam,
Germany |
Chair, Appointed (IGS) |
1999-2002 |
|
|
Norman Beck |
Natural Resources Canada |
Network Representative |
2002-2005 |
|
|
Gerhard Beutler |
University of Bern, Switzerland |
IAG Representative |
--- |
|
|
Claude Boucher |
Institut Geographique National,
ITRF, France |
IERS Representative to IGS |
--- |
|
|
Carine Bruyninx |
Royal Observatory, Belgium |
IGS Representative to the IERS |
2000-2003 |
|
|
Mark Caissy |
Natural Resources Canada |
Real-time Working Group, Chair |
2001-2002 |
|
|
Loic Daniel |
Institut Geographique National,
ITRF, France |
Data Center Representative |
2002-2005 |
|
|
John Dow |
ESA/European Space Operations
Center, Germany |
Network Representative |
2000-2003 |
|
|
Joachim Feltens |
ESA/European Space Operations
Center, Germany |
Ionosphere Working Group, Chair |
1999-2002 |
|
|
Remi Ferland |
Natural Resources Canada |
IGS Reference Frame Coordinator |
1999-2002 |
|
|
Gerd Gendt |
GeoForschungsZentrum Potsdam,
Germany |
Troposphere Working Group, Chair |
1999-2002 |
|
|
Tom Herring |
Massachusetts Institute of
Technology, USA |
IAG Representative |
--- |
|
|
John Manning |
Australian Survey and Land
Information Group |
Appointed (IGS) |
2000-2003 |
|
|
Ruth Neilan |
IGS Central Bureau, Jet Propulsion
Laboratory |
Director of IGS Central Bureau |
--- |
|
|
To be appointed |
|
FAGS Representative |
--- |
|
|
Carey Noll |
Goddard Space Flight Center, USA |
Data Center Working Group, Chair |
2002-2004 |
|
|
Jim Ray |
U. S. Naval Observatory, USA |
Analysis Representative & |
2002-2005 |
|
|
Markus Rothacher |
Technical University of Munich,
Germany |
Analysis Representative |
2000-2003 |
|
|
Tilo Schoene |
GeoForschungsZentrum Potsdam,
Germany |
TIGA Pilot Project, Chair |
2001-2003 |
|
|
Robert Serafin |
Natl. Center for Atmospheric
Research, USA |
Appointed (IGS) |
1998-2005 |
|
|
Jim Slater |
Natl. Imagery and Mapping Agency,
USA |
GLONASS Pilot Project, Chair |
2000-2002 |
|
|
Robert Weber |
University of Bern, Switzerland |
Analysis Center Coordinator |
2001-2002 |
|
|
To be appointed |
|
LEO Working Group, Chair |
1999-2000 |
|
|
Peizhen Zhang |
China Seismological Bureau,
Insitute of Geology |
Appointed (IGS) |
2002-2005 |
|
|
Jim Zumberge |
Jet Propulsion Laboratory, USA |
Analysis Representative |
2000-2003 |
|
|
Angelyn Moore |
IGS Central Bureau, Jet Propulsion
Laboratory |
Board Secretariat, Network
Coordinator |
--- |
|
|
FORMER GB MEMBER |
INSTITUTION & COUNTRY |
SERVICE |
|
Yehuda Bock |
Scripps Institution of
Oceanography, USA |
1994-1999 |
|
Mike Bevis |
University of Hawaii, USA |
1998-2001 |
|
Geoff Blewitt |
University of Nevada, Reno, USA |
1996-2001 |
|
Bjorn Engen |
Norwegian Mapping Authority |
1994-2001 |
|
Martine Feissel |
International Earth Rotation
Service, France |
1994-1995 |
|
Teruyuki Kato |
Earthquake Research Institute,
University of Tokyo, Japan |
1994-1995 |
|
Jan Kouba |
Natural Resources Canada |
1994-1999 |
|
Gerry Mader |
National Geodetic Survey, National
Oceanic and Atmospheric Administration, USA |
1994-1997 |
|
Bill Melbourne |
Jet Propulsion Laboratory, USA |
1994-1999 |
|
Ivan Mueller |
Ohio State University, USA |
1994-1999 |
|
Paul Paquet |
Royal Observatory of Belgium |
1999-2002 |
|
David Pugh |
Southhampton Oceanography Center,
UK |
1996-1998 |
|
Bob Schutz |
Center for Space Research, University
of Texas-Austin, USA |
1994-1997 |
|
Tim Springer |
University of Bern, Switzerland |
1999-2000 |
|
Mike Watkins |
Jet Propulsion Laboratory, USA |
1999-2001 |
|
Pascal Willis |
Institut Geographique National,
France |
1999 |
Table 2. IGS Product Tables 2002
GPS Satellite Ephemerides/Satellite
& Station Clocks
[GPS Broadcast values included for
comparison]
|
|
ACCURACY |
LATENCY |
UPDATES |
SAMPLE INTERVAL |
|
Broadcast |
~260 cm/~7 ns |
real time |
-- |
daily |
|
Predicted (Ultra-Rapid) |
~25 cm/~5 ns |
real time |
twice daily |
15 min/15 min |
|
Rapid |
5 cm/0.2 ns |
17 hours |
daily |
15 min/5 min |
|
Final |
<5 cm/0.1 ns |
~13 days |
weekly |
15 min/5 min |
GLONASS Satellite Ephemerides
|
Final |
30 cm |
~4 weeks |
weekly |
15 min |
Geocentric Coordinates of IGS
Tracking Stations (>130 sites)
|
Final horizontal/vertical positions |
3 mm/6 mm |
12 days |
weekly |
weekly |
|
Final horizontal/vertical
velocities |
2 mm per yr/3 mm per yr |
12 days |
weekly |
weekly |
Earth Rotation Parameters
|
Rapid polar motion/PM rates/ |
0.2 mas/0.4 mas per day/ |
17 hours |
daily |
daily |
|
length-of-day |
0.030 ms |
|
|
|
|
Final polar motion/PM rates/ |
0.1 mas/0.2 mas per day/ |
~13 days |
weekly |
daily |
|
length-of-day |
0.020 ms |
|
|
|
Atmospheric Parameters
|
Final tropospheric |
4 mm zenith path delay |
< 4 weeks |
weekly |
2 hours |
Ionospheric TEC grid (under development)
Table 3. The IGS Analysis Centers
|
IGS Analysis Centers |
|
|
CODE Astronomical
Institute-University of Bern |
Switzerland |
|
European Space Operations Center /
European Space Agency |
Germany |
|
FLINN Analysis Center, Jet
Propulsion Laboratory/Caltech,NASA |
USA |
|
GeoForschungsZentrum Potsdam |
Germany |
|
National Geodetic Survey,
Geosciences Research Lab, NOAA |
USA |
|
Natural Resources Canada |
Canada |
|
US Naval Observatory |
USA |
|
Scripps Institution of
Oceanography |
USA |