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The International GNSS Service in a changing landscape of Global Navigation Satellite Systems

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The International GNSS Service (IGS) is an international activity involving more than 200 participating organisations in over 80 countries with a track record of one and a half decades of successful operations.
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The International GNSS Service (IGS) in
a Changing Landscape of Global
Navigation Satellite Systems
J.M. Dow1, R.E. Neilan2, C. Rizos3
1ESA/ESOC, Darmstadt, Germany; 2NASA/JPL, Pasadena, USA; 3School of Surveying & Spatial
Information Systems, University of New South Wales, Sydney, Australia
ABSTRACT
The International GNSS Service (IGS) is an
international activity involving more than 200
participating organisations in over 80 countries with a
track record of one and a half decades of successful
operations. The IGS is a service of the International
Association of Geodesy (IAG). It primarily supports
scientific research based on highly precise and
accurate Earth observations using the technologies of
Global Navigation Satellite Systems (GNSS),
primarily the U.S. Global Positioning System (GPS).
The mission of the IGS is “to provide the highest-
quality GNSS data and products in support of the
terrestrial reference frame, Earth rotation, Earth
observation and research, positioning, navigation and
timing and other applications that benefit society”.
The IGS will continue to support the IAG’s initiative
to coordinate cross-technique global geodesy for the
next decade, via the development of the Global
Geodetic Observing System (GGOS), which focuses
on the needs of global geodesy at the mm-level. IGS
activities are fundamental to scientific disciplines
related to climate, weather, sea level change, and
space weather. The IGS also supports many other
applications, including precise navigation, machine
automation, and surveying and mapping. This paper
discusses the IGS Strategic Plan and future directions
of the globally-coordinated ~400 station IGS
network, tracking data and information products, and
outlines the scope of a few of its numerous working
groups and pilot projects as the world anticipates a
truly multi-system GNSS in the coming decade.
INTRODUCTION
The International GNSS Service (IGS) was officially
established in January 1994 as a service of the
International Association of Geodesy (IAG) (IAG,
2008). Since June 1992, the IGS originally known
as the “International GPS Service for Geodynamics”,
from 1999 simply the “International GPS Service”,
and finally since March 2005 the “International
GNSS Service” – has been making freely available to
interested users precision GPS satellite orbit and
clock corrections and other products, see IGS (2008),
Beutler et al. (1999), Dow et al. (2004), Dow et al.
(2005). The origins and early development of the IGS
are described by Beutler et al. (this issue).
The IGS operates as a voluntary, non-commercial,
confederation of about 200 institutions world-wide
(see Figure 1 for a map of the global station
network), self-governed by its members, managed on
a day-to-day basis by the Central Bureau under the
policy guidance of the Governing Board. Each
participating organisation contributes its own
resources: there is no central source of funding.
Since the IGS Governing Board adopted in December
2001 its Strategic Plan, covering the years 2002-
2007, a number of developments taking place inside
and outside the IGS has made it necessary to revise
the plan. A reflection process was initiated at the
2004 Workshop in Bern, Switzerland, continued
through a dedicated session at the 2006 Darmstadt
Workshop, Germany, culminating in a one and a half
day meeting of a specially appointed Strategic
Planning Committee in Pasadena, California, in
September 2006, and a two day Strategic Planning
Retreat of the Governing Board in San Francisco in
December 2006. A new IGS Strategic Plan for the
years 2008-2012 has resulted from this process.
This paper outlines some of the current central
concerns of the IGS and points to the key issues for
the coming years.
THE IGS PRODUCTS
The IGS collects, archives, and distributes GPS and
GLONASS observation data sets of sufficient
accuracy to meet the objectives of a wide range of
scientific and engineering users. These data sets are
analysed and combined to form the IGS products
shown in Table 1 (IGS, 2008).
IGS products support scientific activities such as
improving and extending the International Terrestrial
Reference Frame (ITRF) maintained by the
International Earth Rotation and Reference Systems
Service (IERS); monitoring deformations of the solid
Earth and variations in the liquid Earth (sea level, ice
sheets, etc.) and in Earth rotation; determining orbits
of scientific satellites; and monitoring the
troposphere and ionosphere.
Typical accuracies and latencies of the various
products are indicated in Table 1. The primary IGS
products are the GPS satellites’ IGS Final Orbit and
Clock corrections, now at the cm accuracy level (see
Figure 2 for the recent evolution of orbit accuracy).
The accuracy of a recent orbit solution, together with
some relevant ancillary information, can be seen in
Figure 3.
THE CHANGING GNSS LANDSCAPE
While the IGS product range has been mainly
concerned with GPS, since 1998 GLONASS products
were developed, initially in connection with the
International GLONASS Experiment (IGEX) of 1999
(Slater et al., 2004). This continued seamlessly, from
2001, through the International GLONASS Service
(IGLOS), a pilot project of the IGS, which reached a
successful conclusion in December 2005, when the
GLONASS products (raw data and derived products)
were integrated into the mainstream IGS product
flow (see Table 1). The participation during the past
two years of the Russian Institute IAC in the IGS
GLONASS orbit combination has contributed to
improvements in the quality of these products.
Improvements in the GLONASS geodetic reference
frame PZ 90 are in part due to assimilation of IGS
stations with coordinates well-determined in the
ITRF.
More recently the IGS has been actively following
the development of the European Galileo system, in
three general areas (Dow et al., 2007).
Firstly, the IGS GNSS Working Group and its
individual members are involved in bringing to the
attention of the new GNSS system providers the
experience gained over the past decade and a half in
the IGS concerning orbit models, antenna phase
calibrations, standardisation of data formats and other
matters. This applies to future generation GPS as well
as to Galileo, and to other systems such as China’s
Beidou/Compass, India’s Regional Navigation
Satellite System (IRNSS), and Japan’s Quasi-Zenith
Satellite System (QZSS).
Secondly, European IGS participants contributing to
the global IGS ground station network (ESOC and
GeoForschungsZentrum Potsdam - GFZ) have been
working with European industry and ESA to set up
and operate the network of sensor stations (GIOVE
Experimental Sensor Stations - GESS) to track the
experimental GIOVE satellites. This network,
totalling 13 stations, including 11 on well-tested IGS
sites, has been fully operational since early 2007.
The third area in which IGS has been able to
contribute its expertise is in the Galileo Geodetic
Service Provider (GGSP) Prototype. This is a project
funded by the European GNSS Supervisory
Authority (GSA), with technical management support
from ESA, with the objective of designing and
developing a system capable of providing and
maintaining over the projected 20 year lifetime of the
Galileo system a geodetic reference frame, to be
known as the Galileo Terrestrial Reference Frame
(GTRF). This frame shall be within 3cm (2-sigma) of
the ITRF (IERS, 2008), to which the IGS contributes
on a routine basis the consolidated GPS input. Three
European IGS Analysis Centres (University of Bern,
GFZ Potsdam, ESA/ESOC), as well as key European
institutes involved in the IERS (BKG, IGN),
supported by Canadian and Chinese organisations
(NRCan, University of Wuhan), are working in a
consortium led by the GFZ. A first realisation of the
GTRF, based on GPS data from selected IGS sites,
has been successfully validated. Updates will be
based on inclusion (in addition) of GPS data from the
GIOVE network and then GIOVE data itself. As the
Galileo Sensor Stations (GSS) planned for the
Galileo In-orbit Validation Phase are established,
data from those sites will also be processed and
included. The GGSP will have an important two-way
interface with the Galileo Ground Mission Segment
(GMS), to retrieve the necessary GSS data and to
provide the resulting reference frame information. It
will also provide the interface between the GMS and
the International Laser Ranging Service, in order to
facilitate provision of satellite laser ranging data for
the Galileo spacecraft for calibration purposes.
Further details of the GGSP can be found in Gendt et
al. (2007).
IGS and IAG representatives are active in the
recently established U.S. National Space-based
Position Navigation and Timing Advisory Board,
which provides to the PNT Executive Committee
advice relating to positioning, navigation and timing
(PNT) policy and capabilities (PNT, 2008) .
In addition, the IGS (as well as the IAG and other
international and intergovernmental organisations)
are members of the International Committee on
GNSS (ICG), convened by the U.N. Office of Outer
Space Affairs (UNOOSA, 2008) see below.
IGS WORKING GROUPS & PILOT PROJECTS
The IGS has a number of Working Groups, focused
on different aspects of current GNSS product
generation, as well as Pilot Projects investigating
future developments which could lead to the
generation of new IGS products. The current WGs
are:
Ionosphere Working Group
Troposphere Working Group
IGS Reference Frame Working Group
Low Earth Orbiter (LEO) Working Group
Real Time Working Group
GNSS Working Group
Data Center Working Group
Clock Products Working Group
Calibration and Biases Working Group
The current IGS Pilot Projects are:
Tide Gauge Benchmark Monitoring Project for
Sea Level Studies (TIGA)
Real Time Pilot Project
The charter of each WG and PP describes the goals
and objectives, see IGS (2008). The chairs of the
WGs and PPs report to the IGS Governing Board on
a regular basis.
TOWARDS REAL TIME PRODUCTS
The IGS has been developing the capability for real
time data streaming from the ground station network
for some years. Currently up to 60 stations are
providing data, with a latency of the order of a few
seconds (IGSRT, 2008). A recent development was
the initiation of a Real Time Pilot Project (RT-PP),
which has the following objectives:
Manage and maintain a global IGS real time
GNSS tracking network.
Enhance and improve selected IGS products.
Generate new real time products.
Investigate standards and formats for real
time data collection, data dissemination and
delivery of derived products. Both the
RTIGS and the NTRIP protocols will be
assessed as to their suitability.
Monitor the integrity of IGS predicted orbits
and GNSS status.
Distribute observations and derived products
to real time users, and support Network
DGPS/RTK operations.
Encourage cooperation among real time
activities, particularly in IGS densification
areas.
The Call for Participation in the RT-PP (see IGS,
2008) requested proposals for:
Real time Tracking Stations
Real time Data Centres
Real time Analysis Centres
Real time Associate Analysis Centres
Real time Analysis Centre Coordinator
Real time Network Management and
Monitoring
Real time Users for Assessment, Evaluation
and Feedback
The RT-PP will gather and distribute real time data
and products associated with GNSS satellite
constellations. The primary products envisioned are
multi-frequency observation data and precise satellite
clocks and orbits made available in real time. These
products will be freely available to participants, and
eventually to external users, for any purpose, in
accordance with the IGS open data policy. An
important objective of the RT-PP will be to support
and promote the development of real time
applications. The IGS will work closely with
standards setting bodies such as the RTCM, to ensure
appropriate real time capabilities are implemented in
the next generation of GNSS receivers. The RT-PP
will operate for a period of up to 3 years. Annual
reviews will be conducted by the IGS Governing
Board to assess the project's progress towards
achieving its goals and objectives.
THE IGS NETWORK
The IGS may be unique in its commitment to
inclusiveness and a vendor-neutral stance toward
instrumentation. This permits participation by a wide
variety of agencies, universities, and individuals. It
also results in a large and heterogeneous network of
equipment that presents certain calibration,
standardization, and coordination challenges. A
typical IGS site consists of a monument, antenna,
receiver, an ultra-stable clock (in many cases a
hydrogen maser or rubidium or cesium atomic clock)
and optionally a computer and communications
device. The monument is the stable connection of the
antenna to a point on the ground. Monument types
include pillars, braced-rod types, and building
mounts. Antennas and receivers from a variety of
commercial manufacturers are dual-frequency and
record both code and phase from the GPS and
optionally GLONASS satellites. Not all types of
equipment are suitable for the most demanding
precise geophysical applications; more information is
available at the IGS station guidelines (IGS, 2008).
Since IGS stations must return data on a daily basis,
they are connected to communications suitable to
support this. Internet, telephone, radio, and satellite
communications are variously employed according to
each site's characteristics. Obviously real time data
streaming by stations participating in the RT-PP is a
significant communications challenge for some
stations .
What are some of the issues facing the IGS tracking
network in the context of the “changing landscape”
of GNSS? The authors list the following:
What will be the characteristics of the future
IGS-type geodetic receiver? What
transmitted signals will it track?
What is the most suitable station monument
for future IGS stations? Need they all be
constructed to the highest possible stability
standards? Or is it likely that there may be
several “tiers” of IGS station types?
How to define “minimum operational
requirements” for IGS stations for an era
where the quality of derived IGS products
must increase significantly in order to satisfy
the goals of GGOS (see below)? Are there
generally accepted standards for data
quality, or other quality metrics, that can be
adhered to?
How to manage the potentially disruptive
process of station upgrade (in particular
changes in antenna type) as new receivers,
tracking next generation GNSS signals, are
progressively installed?
How to encourage the establishment of more
IGS stations in parts of the world where
there is currently a lower density? In
particular in Africa, Russia, and parts of
East and S.E. Asia, with a real time data
streaming capability.
Can there ever be “too many” IGS stations?
What station spacing does that correspond
to?
How to best integrate the operations of IGS
stations in areas where there are already
dense receiver networks, such as the western
United States and parts of Europe?
IGS AND THE GLOBAL GEODETIC
OBSERVING SYSTEM
In parallel with these IGS internal developments, the
IGS has been working with the IAG on the design of
the Global Geodetic Observing System (GGOS)
(GGOS, 2008), which would integrate the activities
and products of the IAG Services and Commissions
(IAG, 2008) in order to provide the contribution of
geodesy to the Global Earth Observing System of
Systems (GEOSS) now being established by the
inter-governmental Group on Earth Observations
(GEO). The ITRF (in particular, its future evolution,
and its correct and consistent use) is a central issue of
the GGOS initiative. The IGS, with its prime concern
for high accuracy and high reliability processing of
the signals of the GNSS constellations and as
provider of the consolidated inputs of the GNSS
contribution to the ITRF, will necessarily play a key
role in GGOS.
The work of the IGS and its constituent elements is
becoming even more relevant to global societal issues
which are driving the need for a better understanding
of the Earth System” in which we live. The IGS,
though its participation in the GGOS effort, can
contribute in areas such as climate change, global
mass transport, sea level rise, measuring surface
geodynamics at a range of spatial scales, geohazard
prediction and monitoring, and natural disaster
mitigation (earthquakes, volcanoes, tsunamis, etc.)
THE INTERNATIONAL COMMITTEE ON
GNSS
Another recent development is the establishment of
the International Committee on GNSS (ICG), which
was officially established through the United Nations
Office of Outer Space Affairs (UNOOSA) in
December 2005, following extensive preparatory
meetings and actions over several years in which the
IGS played an active role. The members of the ICG
are the developers (or “providers”) of the GNSS
systems and several other interested UN member
states, while associate members are mainly inter-
governmental and non-governmental organisations
representing primarily users of GNSS, such as the
IGS, IAG, etc. (UNOOSA, 2008).
Three meetings of the ICG have taken place, the first
at the United Nations center in Vienna, Austria, in
November 2006, the second in Bangalore, India, in
early September 2007, and the third in Pasadena,
California, in early December 2008. Significant
issues (from the point of view of the IGS) that were
discussed included standardisation of geodetic and
time reference frames. Three recommendations
relevant to these issues were adopted in the final
plenary session.
The IGS is thus playing an even more active role in
the international context of GNSS. The latter itself is
changing rapidly, with further improvements of the
GPS system (GPS IIM, GPS IIF, GPS III satellite
constellations), the revival of the Russian GLONASS
(likely to reach a complete constellation again in the
next year or two, with additional system
developments on the horizon, including a possible
move to CDMA signals), the European Galileo
system of 30 satellites, and global or regional systems
being developed by Japan, China and India, among
others. High on the international agenda is the
compatibility and (where possible) interoperability of
these systems. The IGS will continue to take an
active role in monitoring the progress of these
systems, investigating their utility for the highest-
quality GNSS products and services, and in providing
its experience and expertise, in particular with
regards to the support of high-accuracy research and
applications based on the analysis of GNSS signals.
The IGS, as a source of independent expertise on
matters related to GNSS technology and its
application to reference frame definition, will be an
important partner in global initiatives such as
AFREF. This project seeks to establish a single, high
quality geodetic reference frame for the whole of the
African continent. In partnership with Africa’s
national surveying and mapping agencies, and
international associations such as the IAG and the
International Federation of Surveyors (FIG), the IGS
is encouraging the establishment of a network of
continuously operating GNSS reference stations
across the continent. This network will provide the
raw observations which, when processsed together
with IGS products such as precise GNSS orbits, will
underpin all future geospatial data gathering,
geoscientific studies and navigation operations in
Africa.
THE IGS STRATEGIC PLAN 2008-2012
Although much of the IGS Strategic Plan 2002-2007
remains valid, a new Plan was developed during
2006-7. A mission statement and six long-term goals
were formulated (see text box).
MISSION
The International GNSS Service provides the
highest-quality GNSS data and products in
support of the terrestrial reference frame, Earth
rotation, Earth observation(s) and research,
positioning, navigation and timing and other
applications that benefit society.
LONG-TERM GOALS
1. Serve as the premier source of the highest-
quality GNSS related standards (conventions),
data and products, openly available to all user
communities.
2. Attract leading-edge expertise to pursue
challenging, innovative projects in a collegial,
collaborative and creative culture.
3. Incorporate and integrate new systems,
technologies, applications and changing user
needs into IGS products and services.
4. Facilitate the integration of IGS into GGOS and
other more broadly based Earth observing and
global navigation systems and services.
5. Maintain an international federation with
committed contributions from its members, and
with effective leadership, management and
governance.
6. Promote the value and benefits of IGS to society,
the broader scientific community, and in
particular to policy makers and funding entities.
Based on these, the new Plan identifies three key
strategies:
1. Deliver world-standard quality GNSS data
and products to all users globally with
leading-edge expertise and resources.
2. Develop, integrate, and participate with new
and changing GNSS systems and user needs
to continuously improve IGS services and to
provide value to a broad range of users.
3. Continuously improve the effectiveness of
IGS management and governance to support
future growth.
The broad objectives remain unchanged, however a
significant number of the derived actions are new.
The full Plan will be available shortly on the IGS
website, as well as in printed form.
The implementation of the Strategic Plan will be
aided by the formulation and execution of annual
Implementation Plans, in which the principal targets
for the various elements and projects will be defined
for each calendar year.
CONCLUDING REMARKS
The IGS is continuing its mission of providing
highest-quality GNSS data and products in support of
the terrestrial reference frame; Earth observations and
research; positioning, navigation and timing; and
other applications that benefit society. The changing
landscape of global navigation satellite systems
necessitates that the IGS become even more involved
with international developments. Long-standing
activities are being consolidated and new directions
defined. This is documented and supported by the
recently developed IGS Strategic Plan 2008-2012.
REFERENCES
IAG (2008) www.iag-aig.org
IGS (2008) www.igs.org or igscb.jpl.nasa.gov
Beutler, G., Rothacher, M., Schaer, S., Springer,
T.A., Kouba, J., Neilan, R.E. (1999) The
International GPS Service (IGS): An interdisciplinary
service in support of Earth sciences. Adv. Space Res.
23(1999), 631-635.
Dow, J.M., Gendt, G., Moore, A., Neilan, R.E.,
Weber, R. (2004) The International GPS Service –
What’s next? 10th anniversary assembly charts future
directions. Proc. of ION GNSS 2004, Long Beach,
CA, USA, 21-24 September, 1741-1748.
Dow, J.M., Neilan, R.E., Gendt, G. (2005) The
International GPS Service: Celebrating the 10th
anniversary and looking to the next decade. Adv.
Space Res. 36(2005) 320-326.
Slater, J.A., Weber, R., Fragner, D. (2004) The IGS
GLONASS Pilot Project Transitioning an
experiment into an operational GNSS service. Proc.
of ION GNSS 2004, Long Beach, CA, USA, 21-24
September, 1749-1757.
Dow, J.M., Neilan, R.E., Weber, R., Gendt, G. (2007)
Galileo and the IGS: Taking advantage of multiple
GNSS constellations. Adv. Space Res. 39(2007),
1545-1551.
IERS (2008) www.iers.org
Gendt, G., Soehne, Rothacher, M., and GGSP
Prototype Team (2007) Realisation and maintenance
of the Galileo Terrestrial Reference Frame (GTRF).
Proc. of 1st Colloquium on Scientific and
Fundamental Aspects of the Galileo Programme,
Toulouse, France, 1-4 October.
PNT (2008) http://pnt.gov
UNOOSA (2008) International Committee on GNSS
(ICG) website:
www.unoosa.org/oosa/en/SAP/gnss/icg.html
IGSRT (2008) http://www.rtigs.net
GGOS (2008) http://www.ggos.org
Beutler, G., Moore, A.W., Mueller, I.I (2008) The
International Global Navigation Satellite Systems
(GNSS) Service: Developments and achievements
(this issue)
Acknowledgements The continuing contribution of
very many individuals from many organisations
world-wide to maintaining the high quality of the
IGS products is gratefully acknowledged.
Table 1: IGS Product Summary
Accuracy
Latency
Updates
GPS Satellite Ephemerides/
Satellite & Station Clocks
orbits
~160cm
Broadcast
Sat. clks
~7ns
real time
--
orbits
~10cm
Ultra-Rapid
(predicted
half)
Sat. clks
~5ns
real time
four x daily
orbits
<5cm
Ultra-Rapid
(observed half)
Sat. clks
~0.2ns
3 hours
four x daily
orbits
<5cm
Rapid
Sat. & Stn.
clks
0.1ns
17 hours
daily
orbits
<5cm
Final
Sat. & Stn.
clks
<0.1ns
~13 days
weekly
GLONASS Satellite Ephemerides
Final
15cm
2 weeks
weekly
Geocentric Coordinates of IGS Tracking Stations
(>130 sites)
horizontal
3mm
Final positions
vertical
6mm
12 days
weekly
horizontal
2mm/yr
Final velocities
vertical
3mm/yr
12 days
weekly
Earth Rotation Parameters
PM
0.3mas
PM rate
0.5mas/day
Ultra-Rapid
(predicted
half)
LOD
0.06ms
real time
four x daily
PM
0.1mas
PM rate
0.3mas/day
Ultra-Rapid
(observed half)
LOD
0.03ms
3 hours
four x daily
PM
<0.1mas
PM rate
<0.2mas/day
Rapid
LOD
0.03ms
17 hours
daily
PM
0.05mas
PM rate
<0.2mas/day
Final
LOD
0.02ms
~13 days
weekly
Atmospheric Parameters
Final tropospheric zenith path
delay
4mm
< 4 weeks
weekly
Ultra-Rapid tropospheric
zenith path delay
6mm
2-3 hours
every 3
hours
Final Ionospheric TEC grid
2-8TECU
~11 days
weekly
Rapid Ionospheric TEC grid
2-9TECU
<24 hours
daily
Figure 1: Global distribution of stations of the IGS network
Figure 2: Improvement of IGS Final Orbits with time (since GPS week 700)
Figure 3: Accuracy of a typical recent Ultra Rapid IGS Orbit Combination, by satellite
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In this study, 15 consecutive days of GPS/Galileo observations of three different International GNSS Service (IGS) stations selected at different latitudes were used, and these observations were evaluated in static mode using both traditional-PPP and PPP-AR techniques. In order to evaluate the effect of short and long observation duration on discussed the methods, observation files obtained from three different stations were divided into 0.75, 1, 1.5, 2, 3, 4 and 24 hour data. In order to examine the contribution of Galileo satellite observations to GPS satellite observations, PPP and PPP-AR methods were also examined in terms of GPS-only and GPS/Galileo satellite combinations. The results showed that with the increase of the observation duration, the position accuracy increased in the PPP method and the risk of fixing wrong integer ambiguity in the PPP-AR technique was reduced. The findings of the study clearly state that in PPP and PPP-AR techniques, the inclusion of Galileo observations to GPS has improved the positioning accuracy, and when the PPP and PPP-AR methods are compared with each other, the horizontal positioning accuracy of the PPP-AR method is generally better than the PPP method at all observation periods.
... The ephemeris of the broadcast navigation data is not precise enough to correct these errors, because the network used to estimate the broadcast corrections is made up of only a few stations in the world. However, a number of organizations including the IGS [49] provide more precise estimated corrections using a larger network of stations, in real-time or for post-processing purposes. These corrections have the advantage of requiring very low data exchange and can be applied regardless of the distance between the user and the nearest reference station. ...
Thesis
Precise positioning with a stand-alone GPS receiver or using differential corrections is known to be strongly degraded in an urban or sub-urban environment due to frequent signal masking, strong multipath effect, frequent cycle slips on carrier phase, etc. The objective of this Ph.D. thesis is to explore the possibility of achieving precise positioning with a low-cost architecture using multiple installed low-cost single-frequency receivers with known geometry whose one of them is RTK positioned w.r.t an external reference receiver. This setup is thought to enable vehicle attitude determination and RTK performance amelioration. In this thesis, we firstly proposed a method that includes an array of receivers with known geometry to enhance the performance of the RTK in different environments. Taking advantage of the attitude information and the known geometry of the installed array of receivers, the improvement of some internal steps of RTK w.r.t an external reference receiver can be achieved. The navigation module to be implemented in this work is an Extended Kalman Filter (EKF). The performance of a proposed two-receiver navigation architecture is then studied to quantify the improvements brought by the measurement redundancy.This concept is firstly tested on a simulator in order to validate the proposed algorithm and to give a reference result of our multi-receiver system’s performance. The pseudo-range measurements and carrier phase measurements mathematical models are implemented in a realistic simulator. Different scenarios are conducted, including varying the distance between the 2 antennas of the receiver array, the satellite constellation geometry, and the amplitude of the noise measurement, in order to determine the influence of the use of an array of receivers. The simulation results show that our multi-receiver RTK system w.r.t an external reference receiver is more robust to noise and degraded satellite geometry, in terms of ambiguity fixing rate, and gets a better position accuracy under the same conditions when compared with the single receiver system. Additionally, our method achieves a relatively accurate estimation of the attitude of the vehicle which provides additional information beyond the positioning.In order to optimize our processing, the correlation of the measurement errors affecting observations taken by our array of receivers has been determined. Then, the performance of our real-time single frequency cycle-slip detection and repair algorithm has been assessed. These two investigations yielded important information so as to tune our Kalman Filter.The results obtained from the simulation made us eager to use actual data to verify and improve our multi-receiver RTK and attitude system. Tests based on real data collected around Toulouse, France, are used to test the performance of the whole methodology, where different scenarios are conducted, including varying the distance between the 2 antennas of the receiver array as well as the environmental conditions (open sky, suburban, and constrained urban environments). The thesis also tried to take advantage of a dual GNSS constellation, GPS and Galileo, to further strengthen the position solution and the reliable use of carrier phase measurements. The results show that our multi-receiver RTK system is more robust to degraded GNSS environments. Our experiments correlate favorably with our previous simulation results and further support the idea of using an array of receivers with known geometry to improve the RTK performance.
... Ces réseaux viennent compléter les mesures nationales des autres pays frontaliers : Suisse (réseau AGNES, Brockmann et al., 2012), et Italie (réseau RING, http ://ring.gm.ingv.it). Plusieurs réseaux internationaux regroupentégalement les données de stations nationales dans les Alpes occidentales tels que le réseau international IGS (Dow et al., 2009), le réseau européen EUREF-EPN (Bruyninx et al., 2012(Bruyninx et al., , 2013, ou disposent de stations propres (par exemple réseau GAIN du projet européen INTERREG IIIB). Ensemble, ils ont tout d'abord permis de confirmer la surrection observée dans les 31 CONTEXTE ET PROBLÉMATIQUES DE LA THÈSE données de nivellement, puis d'améliorer notre connaissance de l'amplitude des vitesses associées et de préciser ses variations spatiales. ...
Thesis
La chaîne alpine est l'une des premières à avoir été instrumentées au monde, à la fois par géodésie spatiale et par sismologie, principalement en raison de sa sismicité modérée mais régulière. A partir de la grande quantité de données de géodésie spatiale et de sismologie aujourd'hui disponibles, il est désormais possible d’établir un champ de déformation 3D haute résolution de la croûte supérieure dans les Alpes occidentales. Ce champ, constitué des mesures géodésiques de déformation de surface, et des caractéristiques de déformation sismique, doit permettre d'établir les liens entre déformations horizontale, verticale, et sismicité. Nous utilisons au cours de cette thèse une approche multidisciplinaire, basée sur 25 années d'enregistrements sismiques, 20 années de mesures GPS (Global Positioning System) de campagne et permanentes, et 4 années d'acquisitions satellitaires Sentinel-1 pour contraindre le champ de déformation 3D correspondant.L’analyse de la déformation sismique à partir de la base de données Sismalp a permis d’atteindre une résolution de la variabilité spatiale du style de déformation inégalée jusqu’ici dans les Alpes occidentales. Au centre de la chaîne, le calcul des mécanismes au foyer et leur inversion en termes de contraintes principales montrent pour la première fois une orientation de l'extension systématiquement défléchie par rapport à l'axe normal à la chaîne, apportant ainsi des éléments novateurs en termes d’implications géodynamiques. L'interpolation bayésienne du mode de déformation sismique en surface et en profondeur révèle un mode décrochant dextre prédominant sur le pourtour de l'arc alpin occidental, associé à un mode compressif uniquement localisé.Le traitement des données GPS de quatre campagnes de mesures (1996, 2006, 2011, 2016), conjointement aux solutions permanentes RENAG (Réseau National GPS permanent), a permis d’augmenter la résolution des champs de vitesses et de déformation de surface à l’échelle des Alpes occidentales. Il apparaît que le maximum de déformation horizontale est localisé dans le Briançonnais et est compatible avec de la déformation intersismique accommodée par au moins une faille (Faille de la Haute Durance). La comparaison des taux de sismicité issus des mesures GPS et de ceux issus des catalogues de sismicité confirme que, à l'échelle locale et en prenant en compte les incertitudes respectives, la déformation sismique peut être suffisante pour expliquer la déformation horizontale observée dans le Briançonnais. Toutefois à l'échelle de l'arc alpin occidental, les taux de déformation géodésiques demeurent un ordre de grandeur supérieurs aux taux de déformation sismique déduits à la fois des périodes instrumentale et historique.Le traitement en interférométrie satellitaire de quatre années consécutives de données Sentinel-1, quant à lui, a permis pour la première fois dans cette région de s’affranchir de la couverture neigeuse et végétale pour obtenir une carte de vitesses le long de la ligne de visée du satellite à l’échelle de l'arc alpin occidental. Cette dernière a révélé des variations spatiales de courte longueur d'onde de la surrection dans les Alpes occidentales, corrélées spatialement avec les massifs cristallins externes et avec les variations prédites par plusieurs modèles d'isostasie.Ces travaux ont permis d'augmenter la résolution spatiale des déformations de surface horizontale, verticale et sismique de manière inédite à l'échelle des Alpes occidentales. Le champ de déformation 3D correspondant permet de jeter un regard nouveau sur les processus pouvant être à l’origine de la déformation actuelle de la chaîne alpine, ainsi que d'apporter des contraintes inédites sur les paramètres d'entrée nécessaires au calcul d'aléa sismique.
... Only recently, the Galileo and BeiDou constellations became effectively usable. However, these haven't been yet supported with all mandatory products (precise orbits and clocks) and other models (antenna calibrations, signal biases, satellite attitudes, etc) for real-time or near real-time applications by the International GNSS Service (IGS, [8]). The IGS Multi-GNSS Experiment (MGEX, [9]), succeeded by the MGEX Pilot Project, provides support only with final products, i.e. too late for (near) real-time applications. ...
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We use ground‐based (GNSS, SuperDARN, and ionosondes) and space‐borne (Swarm, CSES, and DMSP) instruments to study ionospheric disturbances due to the 25–26 August 2018 geomagnetic storm. The strongest large‐scale storm‐time enhancements were detected over the Asian and Pacific regions during the main and early recovery phases of the storm. In the American sector, there occurred the most complex effects caused by the action of multiple drivers. At the beginning of the storm, a large positive disturbance occurred over North America at low and high latitudes, driven by the storm‐time reinforcement of the equatorial ionization anomaly (at low latitudes) and by particle precipitation (at high latitudes). During local nighttime hours, we observed numerous medium‐scale positive and negative ionospheric disturbances at middle and high latitudes that were attributed to a storm‐enhanced density (SED)‐plume, mid‐latitude ionospheric trough, and particle precipitation in the auroral zone. In South America, total electron content (TEC) maps clearly showed the presence of the equatorial plasma bubbles, that, however, were not seen in data of Rate‐of‐TEC‐change index (ROTI). Global ROTI maps revealed intensive small‐scale irregularities at high latitudes in both hemispheres within the auroral region. In general, the ROTI disturbance “imaged” quite well the auroral oval boundaries. The most intensive ionospheric fluctuations were observed at low and mid‐latitudes over the Pacific Ocean. The storm also affected the positioning accuracy by GPS receivers: during the main phase of the storm, the precise point positioning error exceeded 0.5 m, which is more than five times greater as compared to quiet days.
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We validated the GPS leveling as an alternative to the traditional geometric leveling method. Validation compares the geometric slopes derived from the GNSS positioning technique, heights resulting from geometric leveling campaigns and geoid undulations extracted from the Global Geopotential Model EGM08. This analysis was performed in the Ecuadorian mainland, where we identified areas in which the gradient of the geoidal undulation is less pronounced. The spatialization of the gradient or variation-based methods allowed to analyze the performance of the GPS leveling method, under the hypothesis that less variability in geoid undulation implies less discrepancies in the GPS unevenness. GNSS observations were determined on the leveling plates belonging to the Basic Vertical Control Network. The results of the study are given based on the relative error resulting from the comparison of the traditional differential leveling method with the corresponding values obtained from the GNSS positioning, considering different distances for the spread of unevenness.
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The International GNSS Service (IGS) is an international activity involving more than 200 participating organisations in over 80 countries with a track record of one and a half decades of successful operations. The IGS is a service of the International Association of Geodesy (IAG). It primarily supports scientific research based on highly precise and accurate Earth observations using the technologies of Global Navigation Satellite Systems (GNSS), primarily the US Global Positioning System (GPS). The mission of the IGS is “to provide the highest-quality GNSS data and products in support of the terrestrial reference frame, Earth rotation, Earth observation and research, positioning, navigation and timing and other applications that benefit society”. The IGS will continue to support the IAG’s initiative to coordinate cross-technique global geodesy for the next decade, via the development of the Global Geodetic Observing System (GGOS), which focuses on the needs of global geodesy at the mm-level. IGS activities are fundamental to scientific disciplines related to climate, weather, sea level change, and space weather. The IGS also supports many other applications, including precise navigation, machine automation, and surveying and mapping. This article discusses the IGS Strategic Plan and future directions of the globally-coordinated ~400 station IGS network, tracking data and information products, and outlines the scope of a few of its numerous working groups and pilot projects as the world anticipates a truly multi-system GNSS in the coming decade.
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After 10 years as a service of the International Association of Geodesy, the International GPS Service IGS is preparing for the future use of multiple integrated Global Navigation Satellite Systems: GPS and its modernization, Galileo and GLONASS. Since 1994, the IGS produces GPS data and products at the highest level of precision and accuracy available anywhere: it provides GPS orbits with 3-5 cm accuracy, sub-centimetre station positions and velocities, and station and satellite clocks at the sub nanosecond level for users worldwide. A similar suite of data and products is available for GLONASS, demonstrating the ability of the IGS to incorporate observations from other GNSSs, such as Galileo. IGS currently consists of over 200 actively contributing organizations in more than 80 countries and a global network of more than 350 stations. The working groups and pilot projects of the IGS demonstrate IGS involvement in applications related to the global reference frame, timing, ionosphere, atmospheric water vapour, low Earth orbiter precise orbit determination (LEO POD), sea level change measurements, real-time GPS applications and GNSS/Galileo developments.
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Since 21 June 1992 the International GPS Service (IGS) produces and makes available uninterrupted time series of its products, in particular GPS observations from the IGS Global Network, GPS orbits, Earth orientation parameters (components x and y of polar motion, length of day), satellite and receiver clock information, and station coordinates and velocities.At a later stage the IGS started exploiting its network for atmosphere monitoring, in particular for ionosphere mapping and for troposphere monitoring. This is why new IGS products encompass ionosphere maps and tropospheric zenith delays, both with a very high temporal resolution. This development will be even more pronounced through the advent of many space-missions carrying GPS, or combined GPS/GLONASS receivers for various purposes. The achievements of the IGS are only possible through a unique voluntary cooperation of a great number of active organizations.This article gives an informative overview for the broader scientific community of the spectrum of problems that is addressed today using IGS/GPS techniques.
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After a time of uncertainty the European Global Navigation Satellite System (GNSS) Galileo is going to be realized in the next years. Two test satellites - GIOVE A and B - have been placed in the orbit to validate various signals and component. One basic element of the overall Galileo system is the so-called Galileo Terrestrial Reference Frame (GTRF) as the basis for all Galileo products and services. The realization and maintenance of such a TRF has been given to an external consortium, named the Galileo Geodetic Service Provider (GGSP), which consists of seven institutions under the lead of GeoForschungsZentrum Potsdam. The project is funded within the sixth framework programme (FP6) of the European Union and managed by the European GNSS Supervisory Authority (GSA). It will last until May 2009. The GTRF will be a realisation of the International Terrestrial Reference Frame (ITRF) on a position precision level of 3 cm (2 sigma). Since the GTRF will already be required by the time when the first Galileo signals are going to be emitted during the In-Orbit-Validation (IOV) phase, an initial realisation of the GTRF has to be based on other positioning data, notably GPS. In addition to the GTRF, the GGSP will generate additional products and information, such as Earth Rotation Parameters, satellites orbits, clocks for satellites and stations. The presentation describes the strategy for the GTRF realisation following the "state of the art" TRF implementation. Since the Galileo tracking stations, named Galileo Sensor Stations (GSS), will form a sparse global network, it is necessary to densify the network with additional stations to get the highest possible precision and stability for the GTRF. The connection to the ITRF is realized and validated by IGS stations, which are part of the ITRF, and especially by local ties to other geodetic techniques like satellite laser ranging and VLBI. Results from the first analysis campaigns will be shown with special concern to the so- called Galileo Experimental Sensor Stations (GESS) which form the ground network for GIOVE satellites.
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Since 21 June 1992 the International GPS Service (IGS), renamed International GNSS Service in 2005, produces and makes available uninterrupted time series of its products, in particular GPS observations from the IGS Global Network, GPS orbits, Earth orientation parameters (components x and y of polar motion, length of day) with daily time resolution, satellite and receiver clock information for each day with different latencies and accuracies, and station coordinates and velocities in weekly batches for further analysis by the IERS (International Earth Rotation and Reference Systems Service). At a later stage the IGS started exploiting its network for atmosphere monitoring, in particular for ionosphere mapping, for troposphere monitoring, and time and frequency transfer. This is why new IGS products encompass ionosphere maps and tropospheric zenith delays. This development became even more important when more and more space-missions carrying space-borne GPS for various purposes were launched. This article offers an overview for the broader scientific community of the development of the IGS and of the spectrum of topics addressed today with IGS data and products.
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After 10 years as a service of the International Association of Geodesy, the International GPS Service IGS is preparing for the future use of multiple integrated global navigation satellite systems: GPS and its modernisation, Galileo and GLONASS. Since 1994, the IGS produces GPS data and products at the highest level of precision and accuracy available anywhere: it provides GPS orbits with 3–5 cm accuracy, sub-centimetre station positions and velocities, and station and satellite clocks at the sub-nanosecond level for users world-wide. A similar suite of data and products is available for GLONASS, demonstrating the ability of the IGS to incorporate observations from other GNSSs, such as Galileo. IGS affirms its interest to contribute to the development and applications of the Galileo programme and other GNSS. IGS currently consists of over 200 actively contributing organizations in more than 80 countries and a global network of more than 350 stations. The working groups and pilot projects of the IGS demonstrate IGS involvement in applications related to the precise global reference frame, timing, ionosphere, atmospheric water vapour, low Earth orbiter precise orbit determination (LEO POD), sea level change measurements, real-time GPS applications, and GNSS developments.
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The paper reviews some objectives and preparatory activities of the International GNSS Service (IGS), in relation to the developing European Global Navigation Satellite System Galileo. Experience already acquired in the IGS in monitoring multiple global navigation satellite systems (GPS and GLONASS) is reviewed. Some significant features of the Galileo system are outlined, including constellation design, and some areas are identified in which Galileo will influence IGS operations in the future and in which the IGS and its active elements can continue to contribute to new GNSS developments. These include the IGS GNSS Working Group, the Galileo System Test Bed GSTB-V2 and the Galileo Geodetic Service Provider (GGSP) Prototype.
The International GPS Service -What's next? 10 th anniversary assembly charts future directions
  • J M Dow
  • G Gendt
  • A Moore
  • R E Neilan
  • R Weber
Dow, J.M., Gendt, G., Moore, A., Neilan, R.E., Weber, R. (2004) The International GPS Service -What's next? 10 th anniversary assembly charts future directions. Proc. of ION GNSS 2004, Long Beach, CA, USA, 21-24 September, 1741-1748.
The IGS GLONASS Pilot Project -Transitioning an experiment into an operational GNSS service
  • J A Slater
  • R Weber
  • D Fragner
Slater, J.A., Weber, R., Fragner, D. (2004) The IGS GLONASS Pilot Project -Transitioning an experiment into an operational GNSS service. Proc. of ION GNSS 2004, Long Beach, CA, USA, 21-24
  • G Org Gendt
  • Soehne
  • M Rothacher
  • Ggsp Prototype Team
IERS (2008) www.iers.org Gendt, G., Soehne, Rothacher, M., and GGSP Prototype Team (2007) Realisation and maintenance of the Galileo Terrestrial Reference Frame (GTRF).