Study Group 1.181:
recent years an increasing number of GPS reference stations have been
established on both global and regional scales. Ideally, the latter
should represent local densifications of the International Terrestrial
Reference Frame (ITRF) polyhedron. While at the outset these stations
were built up in most cases to monitor active tectonic regions,
recently the augmentation of real-time surveying and probing of the
atmosphere have become important applications. The website of the
Special Study Group 1.181 is http://www.gmat.unsw.edu.au/snap/gps/iag_section1/ssg1181.htm.
of the SSG 1.181
work of this SSG aims at the tie of regional GPS networks to the
International Terrestrial Reference Frame (ITRF), as well as to study
the ambiguity resolution within a network of multiple reference
stations at baselines with lengths of up to several tens of kilometres.
In particular, the appropriate modelling of ionosphere and troposphere
path delays as the limiting factors for ambiguity resolution, and the
influence of antenna phase centre variations, will be studied.
Concepts and realisations of "virtual reference stations"
will be compared. Real-time kinematic (RTK) solutions within active
reference station networks, the benefits of using combined GPS/Glonass
receivers, as well as the use of predicted IGS orbits will also be
subjects of investigation. Last, but not least, in cooperation with
SSG 1.179, reliable error models of the baseline solutions have to be
formulated. To achieve these goals the SSG will focus on:
the atmospheric modelling part within a network of multiple reference
a website providing SSG related information.
in-depth the concept of "vitual reference stations".
test data sets from regional GPS/Glonass arrays for case studies.
the influence of antenna phase centre variations.
participation in related symposia.
achievements at the IAG Conference in Budapest in 2001, and the next
IUGG General Meeting in 2003.
recommendations and a final report on the SSG's activities.
and Corresponding Members
Robert Weber (Chair, AUSTRIA), Richard Bindley (UK), Heike Bock
(SWITZERLAND), Carine Bruyninx (BELGIUM), Peter CLARKE (UK), Herb
Dragert (CANADA), Galera Monico (BRAZIL), Tom Herring (USA), Horst
Hartinger (AUSTRIA), Paul de Jonge (USA), Ambrus Kenyeres (HUNGARY),
Jan Johnasson (SWEDEN), Lambert Wanninger (GERMANY), Teriyuki Kato
(JAPAN), Elena Ostrovsky (ISRAEL).
Members: Manuel Hernandez-Pajares (SPAIN), Helmut Titz (AUSTRIA), Leos
Mervart (CZECH REPUBLIC)
of the SSG1.181
A Work Program has been proposed by the Chair. Topics
of this WP are:
Reference Frame Issues - how to tie the regional
network to the ITRF.
Impact of the Atmosphere - apriori models / height
Satellite Orbits - errors in satellite orbits,
differences Broadcast and IGS precise/rapid/ultra-rapid orbits.
Parametrisation of Error Sources within a GNSS
Concept of 'Virtual Reference Stations'.
Signal Diffraction and Multipath.
Currently substantial contributions to this Working
Program (including manuscripts and presentations) cover the topics 1,
3, 4, 5 and 6. The Impact of the Atmosphere, and Multipath (as well as
Signal Diffraction) have not been dealt withdue to a only moderate
response of the members to these issues. This might change within the
next two years at least for the atmosphere modelling because of the
upcoming COST Action 716 Demonstration Experiment (troposphere wet
delay) and the Solar Max Campaign (ionosphere). (Although other
SSGs are also active in these areas.)
Test data sets are available from the Chair and several
WG members covering small regional networks in Austria, Switzerland
and parts of the EUREF network. Data sets contain GPS as well as
combined GPS/Glonass data.
A SSG web page has been established primarily for
communication and information of the WG members (for details see http://luna.tuwien.ac.at/ssg1181/ssg1181.htm).
A meeting of the SSG members will take place at the
next IAG Scientific Assembly in Budapest, as well as one meeting in
the USA (AGU Fall Meeting 2001).
plans comprise include the detailed study of the quality of quasi
real-time orbits, as well as their influence on ambiguity resolution
and troposphere modelling. Synergy effects of using data from dual
system (GPS/Glonass) / dual-frequency receivers are also under
final goal over the next two years is to prepare recommendations and a
comprehensive final report on the SSG's activities.