Terms of reference
Section I is concerned with the scientific aspects of the measurement and analysis of regional and global geodetic networks as well as satellite, inertial, kinematic and marine positioning. The practical results of this research work should be made available through recommendations to National Survey Organisations. Applications of geodesy in engineering is a recent new task of Section 1.
Tremendous advances of GPS surveying have occured especially in precision and applicability. However, there are some remaining issues of accuracy and reliability of GPS surveying (hardware and software) which need to be addresses carefully. Recently, GPS measurements have shown the potential to be used as remote sensing tool of atmospheric parameters.
Comm X: Global and Regional Geodetic Networks
SC4: Application of Geodesy to Engineering
Special Study Groups
SSG 1.179: Wide Area Modelling for Precise Satellite Positioning
SSG 1.180: GPS as an atmospheric remote sensing tool
SSG 1.181: Regional Permanent Arrays
SSG 1.182: Multipath Mitigation
Global and Regional Geodetic Networks
President: Claude Boucher (France)
Terms of Reference
The purpose is to focus on the variety of existing control networks (horizontal or vertical, national or continental, global from space techniques) as well as their connections and evolutions.
The commission X has two types of subdivisions: subcommissions and working groups.
In addition, Commission X will have a Steering Committee (SC) consisting of:
|president of the Commission|
|presidents of the Sub-commissions|
|chairmen of the Working Groups|
Each country member of IAG is allowed to appoint one representative to Commission X. If the country belongs to an area where a subcommission has been already established, the representative will be a de facto member of the subcommission. A subcommission is free to have specific rules in addition to those of the whole commission. In particular they may ask for more than one representative for specific reasons.
Each country not yet being a full member of IAG is welcomed to appoint an observer to the Commission.
Members of Working Groups will be selected by the chairmens and approved by the SC after consultation of relevant people and representatives of countries.
GRGN should play mainly a role of stimulation and coordination by helping the dissemination of information, standardization, cooperation and education.
The goals for the 2000-2003 quadriennium are :
President: Claude Boucher (France)
Sub-Commission for South East Asia and Pacific
Working Group on Datums and Coordinate Systems (WG1)
Chair: Bjorn Geir Harrson (Norway)
Working Group on the Worldwide Unification of Vertical Datums (WG3)
Chair:William Kearsley (Australia)
Special Commission SC4
Application of Geodesy to Engineering
President: Heribert Kahmen (Austria)
Secretaries: Zhenglu Zhang (China)
Terms of Reference
Rapid Developments in engineering, microelectronics and the computer sciences have greatly changed both instrumentation and methodology in engineering geodesy. The objectives of the Special Commission are on the one hand to document the body of knowledge in this field and on the other hand to encourage new developments and present them in a conistent frame work. Symposia and workshops will be planned to document the current state of development in engineering applications of geodesy. On the other hand working groups will be established in areas of current research interest which will have special goals so that their research work can be accomplished in a four year period. In addition collaboration with other international organisations as ISPRS, FIG, ION, etc. is planned.
The following working groups are considered as challenging:
Working Group 1 (SC4 WG 1):
Mobile Multi Sensor Systems
Chair: Naser El-Sheimy (Canada)
Co-Chair: Dr. Jan Skaloud (Switzerland)
Terms of Reference
To fulfil the need for up-do-date inventory and geometric data along transportation routes (roads, railways, rivers, pipelines) Mobile Multi-sensor Systems (MMS) are beiong operated. In general, MMS have in common that they integrate a set of sensores mounted on a common platform and synchronized to a common time base. They are typically used in kinematic mode. In principle, they are capable of operating with the data measured on the platform. No other information, such as known ground control, is neede, although it may be included as redundant information. Systems of this type
|can be immediately deployed everywhore on the globe without the need for identifying existing ground control.|
|employ a task-oriented system design through integration at the measurement level. data flow optimitzation can therefore be a built-in feature.|
|can be equipped with real-time quality control features by including data redundancies in the system design and by using a combination of real-time data processing and expert knowledge to get homogeneous results.|
|generally use software georeferencing to transform the time-dependent measurement process into a sequence of georeferenced images which can be considered as independent geometric units in post-mission processing.|
The future and trends of MMS will be the main activity of the working group.
|New developements in Mobile Multi-Sensor Systems|
|New applications for Mobile Multi-Sensor Systems|
|Emerging Processing Techniques for Mobile Multi-Sensor Systems|
Retscher Guenther (Austria)
Larry D. Hothem (USA)
Li Deren (China)
Rongxing Li (USA)
D. Grejner-Brzezinska (USA)
Yi D Huang (UK)
Antonio Vettore (Italy)
S. Puntavungkour (Thailand)
Hans-Gerd Maas (Netherlands)
Sueo Sugimoto (Japan)
C. Vincent Tao (Canada)
Ahmed El-Mowafy (Arab Emirates)
Youcef Hammada (Canada)
Mohamed Aziz (State of Kuwait)
Michael Cramer (Germany)
Craig Glennie (Canada)
Working Group 2 (SC4 WG 2):
Chair: Wolfgang Niemeier (Germany)
Co-Chair: Rainer Flesch (Austria)
The world records for bridge span and building height have increased more than tenfold in the second millenium. In the 20th century alone, the record height for a building has increased from 118 m to 452 m, while the record for a bridge span has increased from 521 m to 1991 m. Both records have increased by factors 3.8 over this period.
As can be seen from these records quality control of these structures is a challenging task. The goals of the monitoring methods are: assessment of the structural behaviour, (safety inspection) and improvement of maintenance (optimization of repair, early detection of damages). The input for the monitoring methodes can be forced or ambient vibrations. Then "Forced Vibration Testing" (FVT and "Ambient Vibration Testing" (AVT) can be applied.
Instruments, used to monitor the motions, are often fixed to the object under motion. That means, their dynamic parameters change depending on the frequencies of the motions.
The goal of this Working Group is, to study dynamic monitoring methodes, sensor systems and system analysis models for quality control of larger structures. Interdisciplinary collaboration will be necessary.
Prof. Dr. Orhan Altan (Turkey)
Mehmet Celebi (U.S.A.)
Dr. Otto Heunecke (Germany)
Svend Kold Kohansen (Denmark)
Dr. Miodrag Roic (Croatia)
Gethin Wyn Roberts (U.K.)
Working Group 3 (SC4 WG 3):
Monitoring of Local Geodynamic
Processes and System Analysis
Chair: Ewald Brückl (Austria)
Monitoring and system analysis of landslides, mudflows and rockslides has become of great importance, since the population of the world is increasing dramatically and, as in many cases, housing estates and industrial sites were erected, without taking these geodynamic processes into consideration.
In mountenous areas, for instance, as in the Alpes, it is assessed that about 6 % of the country is affected by landslides. Alongthe Yangtze River, in the surrounding of the Three Gorges Dam Reservoir, for instance, about 100 landslides have to be monitored. In the average velocities can vary from 1 to 200 mm/year. In general the movements are fairly regular especial in large slopes. In some cases there are reactions according to the climate conditions. However, sometimes instabilities are possible, which cause that the velocities are multiplied by a factor 100 and greater. Sometimes the result is a desaster.
|The main goal of the Working Group is to study|
|Computer controlled Multi-Sensor Systems recording geodetical, geophysical and metheorological data.|
|different models of system analysis and|
|models for desaster prediction.|
Fritz K. Brunner (Austria)
Ladislav Brimich (Slovak Republic)
L. A. Latynina (Russia)
Jussi Kääriänen (Finland)
Heikki Virtanen (Finland)
Carla Braitenberg (Italy)
Károly Dede (Hungary)
Lajos Völgyes (Hungary)
Péter Varga Hungary)
László Bányai (Hungary)
Special Study Group 1.179
Wide Area Modelling for
Precise Satellite Positioning
Chair: S Han (Australia)
Terms of Reference
Precise satellite positioning requires that carrier phase measurements be used and that integer ambiguities of the carrier phase measurements be resolved in some way. However, the distance from the mobile/user receiver to the nearest reference receiver may range from a few kilometres to hundreds of kilometres. As the receiver separation increases, the problems of accounting for distance-dependent biases increase and subsequently reliable ambiguity resolution for carrier phase-based satellite positioning becomes an even greater challenge.
The goal of SSG1.179 is to study different error modelling strategies, to eliminate or mitigate different error sources over short, medium and long user-reference receiver distances for: (1) reliable ambiguity resolution if the errors can be effectively modelled at the centimetre level, and; (2) improvement in the positioning accuracy, if the errors can be modelled at the sub-centimetre level. In addition, the possible need to improve the stochastic model will be addressed, in order to account for residual biases, which can not be done through modifications to the functional model alone.
Error modelling through the improvement of functional models for medium-range, and long-range high precision satellite positioning using multiple reference stations, including:
|multipath mitigation algorithms,|
|troposphere model refinement,|
|regional ionosphere modelling algorithms,|
|orbit bias modelling,|
|parametric modelling algorithms (for each error source), and|
|integer bias estimation and validation, eg., cycle slip detection/repair and ambiguity resolution.|
Error modelling through stochastic model refinement, including:
|correlation analysis of carrier phase measurements from satellite positioning systems,|
|stochastic modelling algorithms suitable for post-processing applications, and|
|stochastic modelling algorithms suitable for real-time applications.|
The continued study of ambiguity resolution techniques in order to develop:
|more efficient means of searching integer ambiguities, and|
|validation procedures for ambiguity resolution.|
The application of these improvements to:
|Short-range satellite positioning applications.|
|Differential correction generation from multiple reference receiver GNSS network, in support of medium-range high precision navigation.|
|Precise long-range GPS kinematic positioning.|
|Sub-millimetre engineering applications, eg, construction deformation monitoring, volcano monitoring, etc.|
The main activities of this group will be:
|Set up a website providing all information related to the SSG activities.|
|Establish a literature reference list for this research focus.|
|Development of questionnaires to determine what algorithms and procedures are actually used, their present performance, and other characteristics.|
|Generating a set of standard data for testing algorithms and procedures.|
|Reporting achievements at symposia, and in particular at the next IAG conference in Budapest in 2001, and submitting the final report at the next IUGG congress in 2003.|
Special Study Group 1.180
GPS as an atmospheric
remote sensing tool
Chair: H van der Marel (The Netherlands)
Terms of Reference
Using networks of ground based GPS receivers it is possible to observe the integrated water vapour (IWV) and the total electron content (TEC) of the Earth's atmosphere. While at first these parameters were considered a mere nuisance, it is nowadays considered to be an important signal for atmospheric sciences.
Water vapour is one of the most important constituents of the atmosphere. It plays a crucial role in many atmospheric processes covering a wide range of temporal and spatial scales. Furthermore, it is also the most important greenhouse gas and highly variable. Climate research and monitoring, as well as operational weather forecasting, need accurate and sufficiently dense and frequent sampling of the water vapour, to which existing GPS networks could contribute significantly. In order to be of any use for operational weather forecasting, firstly GPS networks must be able to provide integrated water vapour in near real-time (with a typical delay of one hour), and secondly GPS observations must be assimilated into numerical weather prediction (NWP) models.
Dual frequency GPS receivers enable the estimation of total electron content (TEC) along a given satellite-receiver signal path. By combining observations from regional and global networks of continuously operating dual frequency receivers, parameters describing the spatial and temporal distribution of total electron content can be derived. Such observations of TEC, available globally on a near real-time basis, allow an excellent opportunity for monitoring ionospheric signatures associated with space weather. For example, the development of ionospheric storms can be observed in global patterns of TEC, while small-scale irregularities in electron density (associated with scintillations) can be observed in short-term variations of TEC and/or spectral analysis of GPS phase observations.
The focus of the SSG is to explore the issues related to
|the derivation of water vapour and TEC in near real-time using GPS,|
|the assimilation of GPS water vapour data into weather forecasting models, and use of GPS water vapour data for climate applications,|
|the integration of GPS-derived TEC estimates and scintillation indices into space weather applications.|
Due to differences in the way the IWV and TEC are derived, it makes sense to organize the work in the special study group into an IWV and a TEC section.
The main objectives of the special study group are:
The activities of the SSG include:
Special Study Group 1.181
Regional Permanent Arrays
Chair: R. Weber (Austria)
Terms of Reference
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 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 more
The work of this study group aims at the tie of regional GPS networks to the ITRF as well as to study ambiguity resolution within a network of multiple reference stations at baselines with a length of up to several tens of kilometres. Especially the appropriate modelling of ionosphere and troposphere path delays as the limiting factors for ambiguity resolution and the influence of antenna phase centre variations should be discussed. Concepts and realisations of virtual reference stations will be compared. RTK solutions within active reference station networks, the benefits of using combined GPS/GLONASS receivers as well as the use of predicted IGS orbits are also the subject of the investigations. Last, but not least, reliable error models of the baseline solutions have to be formulated.
To achieve these goals the SSG will:
|maintain a WWW Homepage,|
|study in-depth the concept of virtual reference stations and the associated atmospheric modelling,|
|provide data from regional GPS/GLONASS arrays operated by the SSG members for case studies, and will collect test data sets,|
|encourage participation in related symposia,|
|prepare recommendations and a comprehensive final report on the SSG's activities.|
Special Study Group 1.182
Chair: M P Stewart (Australia)
Terms of Reference
The precision of raw carrier phase observations recorded by modern GNSS receivers is generally at the sub-millimetre level. However, in all but the most benign environments, the achievable resolution of GNSS positioning is one or more orders of magnitude worse. This discrepancy between the theoretical hardware-dependent precision of the raw observations and the practical accuracy of GNSS position solutions can, in part, be attributed to the effects of site-dependent electromagnetic scattering of incoming GNSS signals. If millimetre level (or better) GNSS accuracies are to be routinely achieved in the future, these electromagnetic scattering effects (commonly referred to as multipath and diffraction) must be eliminated.
The goal of SSG 1.182 is to study GNSS multipath detection and mitigation techniques with the aim of improving existing high precision positioning accuracies. In the context of this SSG, multipath is loosely defined as the systematic errors in raw GNSS observations that are due to any signal scattering effect caused by the local environment surrounding an antenna. Furthermore, this SSG will focus on carrier phase and code-based multipath in terms of effects on receiver operation for high precision applications. Finally, within the scope of the group, the term GNSS is defined to encompass any type of global positioning system (for example, NAVSTAR-GPS, GLONASS-GPS and GALILEO), or systems simulating GNSS signals (such as pseudolite arrays).
These objectives will be achieved by:
|Initiating discussion between SSG members.|
|Setting up an SSG website providing a focus for multipath research with links to member's websites.|
|Providing a comprehensive reference list for multipath studies.|
|Creating a set of standardised multipath data sets to allow comparison between mitigation and detection methods.|
|Setting up a digital library containing all pertinent information on multipath detection and mitigation techniques and technologies.|
The outcome of these activities will be summarised in a final report containing classification of detection and mitigation techniques, a library of results from different environments and receivers, and a set of recommendations giving information on multipath detection and mitigation.