Special Study Group 1.181:




In 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.


Objectives of the SSG 1.181

 The 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:

1.        Studying the atmospheric modelling part within a network of multiple reference stations.

2.        Maintaining a website providing SSG related information.

3.        Studying in-depth the concept of "vitual reference stations".

4.        Providing test data sets from regional GPS/Glonass arrays for case studies.

5.        Investigating the influence of antenna phase centre variations.

6.        Encouraging participation in related symposia.

7.        Reporting achievements at the IAG Conference in Budapest in 2001, and the next IUGG General Meeting in 2003.

8.        Preparing recommendations and a final report on the SSG's activities.


Members and Corresponding Members

 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).

 Corresponding Members: Manuel Hernandez-Pajares (SPAIN), Helmut Titz (AUSTRIA), Leos Mervart (CZECH REPUBLIC)

 Activities 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 correlation.

Satellite Orbits - errors in satellite orbits, differences Broadcast and IGS precise/rapid/ultra-rapid orbits.

Parametrisation of Error Sources within a GNSS Real-Time Network.

Concept of 'Virtual Reference Stations'.

GPS/Glonass integration.

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).

Future 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 investigation.

The final goal over the next two years is to prepare recommendations and a comprehensive final report on the SSG's activities.



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