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Commission 1 - Reference Frames (2007-2011)

URL: http://iag.uni.lu/

posted by
Sz. Rózsa
President: Zuheir Altamimi (France)
Vice President: Mike Craymer (Canada)

Terms of Reference

Reference systems and frames are of primary importance for many Earth science researches and applications, satellite navigation as well as for practical applications in geo-information. A precisely defined reference frame is needed for the quantification of, e.g. Earth rotation and its gravity field, sea level variation, tectonic motion and de
formation, post-glacial rebound, geocentre motion, large scale deformation due to Earthquakes, local subsidence and other ruptures and crustal dislocations. Commission 1 activities and objectives are to deal with theoretical aspects of reference systems and the practical applications for their realizations as well as applied researches.

Commissions 1 will closely interact with the 3 other IAG Commissions, ICCT, Services and GGOS components where reference system aspects are of concern. A close cooperation will be en-forced with international entities that operate and finance space geodesy observatories in order to take all possible measure allowing improving the quality and distribution of the current co-location sites, which constitute the main foundation of the International Terrestrial Reference Frame (ITRF).

Commission 1 is identical with the Sub-commission B2 of the Scientific Commission B of the ICSU Committee on Space Research (COSPAR).


The main objectives of Commission 1 are:
  • Definition, establishment, maintenance and improve-ment of the geodetic reference frames.
  • Advanced terrestrial and space observation technique development for the above purposes.
  • International collaboration for the definition and deployment of networks of terrestrially-based space geodetic observatories.
  • Theory and coordination of astrometric observation for reference frame purposes.
  • Collaboration with space geodesy/reference frame related international services, agencies and organizations.
  • Promote the definition and establishment of vertical reference systems at global level, considering the advances in the regional sub-commissions.


  • SC1.1: Coordination of Space Techniques
    President: Markus Rothacher (Germany)
  • SC1.2: Global Reference Frames
    President: Claude Boucher (France)
  • SC1.3: Regional Reference Frames
    President: João Torres (Portugal)
  • SC1.3 a: Europe
    Chair: Johannes Ihde (Germany)
  • SC1.3 b: South and Central America
    Chair: Claudio Brunini (Argentina)
  • SC1.3 c: North America
    Chairs: Richard Snay (USA), M. Craymer (Canada)
  • SC1.3 d: Africa
    Chair: Richard Wonnacott (South Africa)
  • SC1.3 e: Asia-Pacific
    Chair: Shigeru Matsuzaka (Japan)
  • SC1.3 f: Antarctica
    Chair: Reinhard Dietrich (Germany)
  • SC1.4: Interaction of Celestial and Terrestrial Refer-ence Frames
    President: Harald Schuh (Austria)

Inter-Commission Project:
  • IC-P1.2: Vertical Reference Frames (Joint with Commission 2 and IGFS)
    Chair: Johannes Ihde (Germany)
  • IC-P3.2: Working Group of European Geoscientists for the Establishment of Networks for Earth Science Research (WEGENER) (Joint with Commission 3)
    Chair: Susanna Zerbini (Italy)

Inter-Commission Study Groups:
  • IC-SG1: Theory, Implementation and Quality Assess-ment of Geodetic Reference Frames (Joint with ICCT, IERS)
    Chair: Athanasios Dermanis (Greece)
  • IC-SG2: Quality of Geodetic Multi-Sensor Systems and Networks (Joint with ICCT, Commission 4)
    Chair: Hansjörg Kutterer (Germany)
  • IC-SG3: Configuration Analysis of Earth Oriented Space Techniques (Joint with ICCT, Commissions 3,2)
    Chair: Florian Seitz (Germany)

Inter-Commission Working Groups:
  • IC-WG1.1: Environment Loading: Modelling for Reference Frame and Positioning Applications (Joint with Commission 4 and IERS)
    Chairs: Tonie van Dam (Luxembourg), Jim Ray (USA)
  • IC-WG1.2: Precise Orbit Determination and Reference Frame Definition (Joint with Commission 2)
    Chair: Frank Lemoine (USA)
  • IC-WG1.3: Concepts and Terminology Related to Geodetic Reference Systems
    Chair: Claude Boucher (France)
  • IC-WG1.4: Site Survey and Co-locations (Joint with IERS)
    Chair: Gary Johnston (Australia)

Programme of Activities

The Commission 1 program of activities will include, mainly:
  • Encourage, initiate and support theoretical and ap-plied research activities related to reference frames;
  • Enforce Research and Development activities that im-pact the reference frame determination and its accu-racy as well as the best and optimal usage of reference frame in Earth Science applications;
  • Closely interact with all established IAG Services: IVS, IGS, ILRS, IDS and the IERS, including their Com-bination Centres and Working Groups;
  • Theory and application of the transformation between Celestial and Terrestrial Reference Systems and appli-cation to the consistency between ICRF, ITRF and EOPs, in cooperation with IVS and IERS;
  • Explore advanced combination methodologies of products and raw observations of space geodesy techniques;
  • Investigate all systematic error sources and limitation factors of space geodesy techniques and their combination;
  • Encourage and assist, within each regional sub commission, countries to re-define and modernize their national geodetic systems, compatible with the ITRF
  • Establish a dedicated Web site relating all Commission 1 activities;

Steering Committee

  • President: Zuheir Altamimi (France)
  • Vice President: Mike Craymer (Canada)
  • President SC1.1: Markus Rothacher (Germany)
  • President SC1.2: Claude Boucher (France)
  • President SC1.3: João Torres (Portugal)
  • President SC1.4: Harald Schuh (Austria)
  • Representatives of IERS/IDS/IGS/ILRS/IVS: Werner Gurtner (Switzerland), Chopo Ma (USA), John Ries (USA)
  • Members at large: Shigeru Matsuzaka (Japan), Caudio Brunini (Argentina)


SC 1.1 Coordination of Space Techniques

President: Markus Rothacher (Germany)

Terms of Reference

The space geodetic observation techniques, including Very Long Baseline Interferometry (VLBI), Satellite and Lunar Laser Ranging (SLR/LLR), Global Navigation Satellite Systems (GNSS) such as GPS, GLONASS, and in future GALILEO, the French DORIS, as well as altimetry, InSAR, and the gravity missions, contribute significantly to the knowledge about and the understanding of the three major pillars of geodesy: the Earth's geometry (point coordinates and deformation), Earth orientation and rotation, and the gravity field as well as its time variations. These three fields interact in various ways and they all contribute to the description of processes in the Earth System. Each of the space geodetic techniques contributes in a different and unique way to these three pillars and, therefore, their contributions should be combined into a consistent Global Geodetic Observing System (GGOS), the project of the IAG.

Sub-Commission 1.1 coordinates efforts that are common to more than one space geodetic technique, such as models, standards and formats. It shall study combination methods and approaches concerning links between techniques co-located at fundamental sites, links between techniques co-located onboard satellites, common modelling and parameterisation standards, and perform analyses from the combination of a single parameter type up to a rigorous combination on the normal equation (or variance covariance matrices) and even the observation level. The list of interesting parameters includes site coordinates (e.g. time series of combined solutions), Earth orientation parameters, satellite orbits (combined orbits from SLR, GPS, DORIS, altimetry), atmospheric refraction (troposphere and iono-sphere), gravity field coefficients, geocentre coordinates, etc. One important goal of SC1.1 will be the development of a much better understanding of the interactions between the parameters describing geometry, Earth rotation, and the gravity field as well as the study of methods to validate the combination results, e.g., by comparing them with independent geophysical information.

To the extent possible SC1.1 should also encourage research groups to develop new observation techniques connecting or complementing the existing set of measurements.

Sub-Commission 1.1 has the task to coordinate the activities in the field of the space geodetic techniques in close cooperation with all the IAG Services, especially with the IERS and its Working Group on Combination, and with COSPAR.


The principal objectives of the scientific work of Sub-Commission 1.1 are the following:
  • Study systematic effects of or between space geodetic techniques.
  • Develop common modelling standards and processing strategies.
  • Comparison and combination of orbits derived from different space geodetic techniques together with the IGS LEO Working Group.
  • Explore and develop innovative combination aspects such as, e.g., GPS and VLBI measurements based on the same high-accuracy clock, VLBI observations to GNSS satellites, combination of atmospheric informa-tion (troposphere and ionosphere) of more than one technique, etc.
  • Establish methods to validate the combination results (e.g., with global geophysical fluids data).
  • Explore, theoretically and practically, the interactions between the gravity field parameters, EOPs, and refer-ence frames (site coordinates and velocities), improve the consistency between these parameter groups, and assess, how a correct combination could be performed.
  • Study combination aspects of GPS and InSAR.

Additional objectives of Sub-Commission 1.1 are:
  • Promotion of international scientific cooperation.
  • Coordination of common efforts of the space geodetic techniques concerning standards and formats (together with the IERS).
  • Organization of workshops and sessions at meetings to promote research.
  • Establish bridges and common activities between SC1.1 and the IAG Services.

Links to Services
Sub-Commission 1.1 will establish close links to the relevant services for reference frames, namely International Earth Rotation and Reference Systems Service (IERS), International GPS Service (IGS), International Laser Ranging Service (ILRS), International VLBI Service for Geodesy and Astrometry (IVS), and International DORIS Service (IDS).

Working Groups

  • WG 1.1.1: Comparison and Combination of Precise Orbits Derived from Different Space Geodetic Techniques (joint with the IGS LEO WG)

    This working group is taking over the role of the former CSTG Sub-commission on Precise Orbit Determination (POD) of Low Earth Orbiting (LEO) Satellites. It will work closely together with the IGS LEO Working Group, but will have a broader research field not focussing on GPS, but on the interplay between different tracking tech-niques. The main topics of the WG will be:
    • Comparison and combination of satellite orbits derived from various tracking techniques, including SLR, DORIS, GPS, altimetry, K-band links, CCD, and possible future observation techniques. Satellite orbits ranging from LEOs up to geostationary satellites (GEOs) should be considered.
    • Assessment of systematic errors between different orbit types and observation techniques.
    • Study of improved force models and POD strategies based on the combination of techniques.
  • WG 1.1.2: Interaction and Consistency between Terres-trial Reference Frame, Earth Rotation, and Gravity Field (joint with Commission 2, Commission 3, and GGOS)

    This working group has to be a joint working group to-gether with Commission 2, Commission 3, and GGOS.
    Its main research topics are:
    • Study the theoretical and practical interactions/relationships between parameters and models describing the Terrestrial Reference Frame (TRF), Earth rotation, and the gravity field (e.g., low degree harmonics of the gravity field, Love numbers...).
    • Assess and study the consistency between products of these three fields.
    • Investigate methods and techniques to combine geo-metry, Earth rotation, and gravity field parameters (e.g., by including LEO satellites into global solutions).
  • WG 1.1.3: Comparison and Combination of Atmospheric Information Derived from Different Space Geodetic Techniques (Joint with IGS Troposphere WG, IGS Ionosphere WG, and IVS)

    The task of this working group shall be the comparison and the combination of information about the atmosphere derived from different space geodetic techniques such as GPS, VLBI, InSAR, altimetry, etc. A very close cooperation with the IAG services, especially the IGS and the IVS are essential. Major research topics are:
    • Investigate differences between tropospheric delay parameters estimated by different techniques; assess systematic biases between techniques and the accuracy of each individual technique; consider ways to combine and validate the information of different techniques.
    • Study the accuracy of global or regional ionosphere maps or simple delays derived from different techniques; assess systematic biases; compare, combine, and validate results.

SC 1.2 Global Reference Frames

President: Claude Boucher (France)

Terms of Reference

Sub-Commission 1.2 is engaged in scientific research and practical aspects of the global reference frames. It investigates the requirements for the definition and realization of the terrestrial reference systems (TRS) and frames (TRF), addresses fundamental issues closely related to TRS, such as multi-technique global geodetic observatories (local ties, site effects, interdisciplinary use…) or methods for the combined processing of heterogeneous observation data. The work will be done in close cooperation with the International Earth Rotation and Reference Systems Service (IERS), in particular with the ITRS Product Centre, the other relevant IAG services (IGS, ILRS, IVS, IDS), and the IAG Global Geodetic Observing System (GGOS). Theoretical aspects (e.g., quality measures, relativistic modelling) will be investigated in cooperation with the Inter-Commission Committee on Theory.


The following research topics will form the fundamental objectives during the next period:
  • Basic concepts and related terminology
  • Improvement of relativistic modelling
  • Fundamentals of the realization of the global terrestrial reference frames: co-location problems, local ties, datum problems (origin, scale and orientation, time evolution), coordinates origin, geo-centre, time series approach, long-term consistency with EOPs and ICRF…
  • Analysis of strengths, weaknesses and systematic differences (biases) of individual techniques (VLBI, SLR, GPS, DORIS) related to their contribution to global combined TRF
  • Combination methodologies of individual techniques' solutions and analysis of the underlying models, para-meters, datum definitions etc.
  • TRF by multi-technique data analysis
  • Global Geodetic Observatories, concepts and practical implementation
    Links to Services

Sub-Commission 1.2 will closely be linked to the relevant services, in particular to the International Earth Rotation and Reference Systems Service (IERS), but also to the International GPS Service (IGS), International Laser Ranging Service (ILRS), International VLBI Service for Geodesy and Astrometry (IVS), and International DORIS Service (IDS).

The sub-commission has an open membership. Details about its activities will be given in its web page accessible through the IAG links.
Project, Study and Working Groups linked to SC1.2
  • IC-P 1.2: Vertical Reference Frames
    Chair: Johannes Ihde (Germany)
  • IC-SG 1: Theory, Implementation and Quality Assessment of Geodetic Reference Frames (jointly with ICCT)
    Chair: Athanasios Dermanis (Greece)
  • IC-WG 1.3: Concepts and Terminology related to Geodetic Reference Systems
    Chair: Claude Boucher (France)
  • IC-WG 1.4: Site Survey and Co-location (jointly with IERS)
    Chair: Gary Johnston (Australia)

SC 1.3 Regional Reference Frames

President: João Torres (Portugal)

Terms of Reference

Sub-Commission 1.3 deals with the definitions and reali-zations of regional reference frames and their connection to the global International Terrestrial Reference Frame (ITRF). It offers a home for service-like activities addressing theoretical and technical key common issues of interest to regional organisations.


In addition to specific objectives of each regional sub-commission, the main objectives of SC1.3 as a whole are:
  • Develop specifications for the definition and realization of regional reference frames, including the vertical component with special consideration of gravity data and other data.
  • Coordinate activities of the regional sub-commissions focusing on exchange and share of competences and results.
  • Develop and promote operation of GNSS permanent stations, in connection with IGS whenever appropri-ate, to be the basis for the long-term maintenance of regional reference frames.
  • Promote the actions for the densification of regional velocity fields.
  • Encourage and stimulate the development of the AFREF project in close cooperation with IGS and other interested organizations.
  • Encourage and assist, within each regional sub-commission, countries to redefine and modernize their national geodetic systems, compatible with the ITRF.


Regional Sub-commissions
  • SC1.3a Europe (EUREF)
    Chair: Johannes Ihde (Germany)
    Chair of the Technical Working Group (TWG): Carine Bruyninx (Belgium)
    Secretary: Helmut Hornik (Germany)
  • SC1.3b South and Central America (SIRGAS)
    Chair: Claudio Brunini (Argentina)
    Vice-President: Laura Sanchez (Colombia/Germany)
  • SC1.3c North America (NAREF)
    Co-Chairs: Richard Snay (USA), Michael Craymer (Canada)
  • SC1.3d Africa (AFREF)
    Chair: Richard Wonnacott (South Africa)
  • SC1.3e South-East Asia and Pacific
    Chair: Shigeru Matsuzaka (Japan)
  • SC1.3f Antarctica (SCAR)
    Chair: Reinhard Dietrich (Germany)

Working Group

  • SC1.3-WG1: Regional Dense Velocity Fields
    Chair: Carine Bruyninx (Belgium)

    Programme of Activities
    • Organize inter-regional workshops addressing activi-ties, results and key issues of common interest to the regional sub-commissions.
    • Develop analysis strategies and compare methods for the implementation of the regional reference frames and their expression in the ITRF, with full interaction with the IGS.
    • Consider establishing regional dense velocity fields for, primarily, the long-term maintenance of the regional reference frames.
    • Contribute at regional levels to the realization and im-provement of local surveys in the collocation sites, with full cooperation with the Sub-commission 1.2 Global Reference Frames.
    • SC1.3-WG1: The main task of this WG is to develop harmonized and possibly common specifications for the densification of the regional velocity fields.

SC1.3a Regional Reference Frame for Europe (EUREF)

Chair: Johannes Ihde (Germany)
Chair of the Technical Working Group (TWG): Carine Bruyninx (Belgium)
Secretary: Helmut Hornik (Germany)

Terms of Reference

EUREF, the Regional Reference Frame Sub-commission for Europe, deals with the definition, realization and maintenance of the European Reference Frame. EUREF is focusing on both the spatial and the vertical components in close cooperation with the pertinent IAG components (Services, Commissions, and Intercommission projects) and EuroGeographics, the consortium of the National Mapping and Cadastral Agencies (NMCA) in Europe.

  • EUREF is composed by representatives from European IAG member countries.
  • The TWG (Technical Working Group) is composed by members elected by the plenary, members in charge of special projects and ex-officio members.

Programme of Activities
  • Continue to develop the EUREF Permanent Network (EPN) in close cooperation with IGS, for the mainte-nance of the European Reference Frame, as a contribution to the ITRF and as infrastructure to support other relevant projects, namely the European initiatives related with GALILEO
  • Extend the Unified European Levelling Network (UELN) and prepare it to be computed under a geo-kinematic approach
  • Implement the project European Combined Geodetic Network (ECGN) and investigate the discrepancies already identified in the combination of the EUVN (European United Vertical Network) results and the gravimetric geoid (project EUVN_DA), in close co-operation with IAG Commission 2
  • Establish a dense velocity field model for the long-term maintenance of the European reference frame
  • Consider the contribution to the IAG Program GGOS (Global Geodetic Observing System) using the installed infra-structures managed by the EUREF members
  • Promote the adoption of the reference systems defined by EUREF (ETRS89 - European Terrestrial Reference System 1989 and EVRS -European Vertical Reference System) in the European countries and European-wide organizations involved in geo-referencing activities
  • Organize annual symposia addressing activities carried out at national and European-wide level related with the global work and objectives of EUREF

SC1.3b Regional Reference Frame for South and Central America (SIRGAS)

Chair: Claudio Brunini (Argentina)
Vice-chair: Laura Sánchez (Colombia / Germany)

Terms of Reference

Sub-commission 1.3b (South and Central America) en-compasses the activities developed by the “Geocentric Reference System for the Americas” (SIRGAS). As such, it is concerned with the definition and realization of a unified reference frame for South and Central America, consistent with ITRS/ITRF, and promoting the definition and establishment of a unified vertical reference system in the region.


The main purpose of the Sub-commission 1.3 is the definition, realization, and maintenance of the 3D geocentric reference system for the Americas, including a gravity field-related vertical reference system. This objective comprises:
  • Determination and maintenance of a geocentric reference frame (a set of stations with high-precise geo-centric coordinates [X, Y, Z] and their variation with time [Vx, Vy, Vz]), as a regional densification of the global ITRF.
  • Establishment of the geocentric datum in the member countries defined by the origin, orientation and scale of SIRGAS (i.e. IERS).
  • Definition and realization of a unified vertical refer-ence system composed by consistent physical and geometrical heights, as well as, their variations with time, i.e. [h, Vh, H, VH, N, VN].
  • To promote and coordinate the efforts of the Latin American countries to achieve the defined objectives.


The structure of the sub-commission is based on the functioning bodies of the SIRGAS project. There are currently three Working Groups:
  • SC1.3b-WG1: Reference System
    Chair: Sonia Costa (Brazil)
  • SC1.3b-WG2: Geocentric Datum
    Chair: Tomas Marino (Costa Rica)
  • SC1.3b-WG3: Vertical Datum
    Chair: William Martinez (Colombia)

The SIRGAS steering committee (or council, as it is named in the SIRGAS statutes) is composed by:
  • SC1.3b Chair
  • SC1.3b Vice-Chair
  • SC1.3b-WG1 Chair
  • SC1.3b-WG2 Chair
  • SC1.3b-WG3 Chair

Programme of Activities
  • To improve the coverage and functioning of the SIRGAS Continuously Operating Network (SIRGAS-CON) following the IAG recommendations related with the monumentation, maintenance, and analysis strategies (WG1).
  • To improve the determination of the velocity field for Latin America, based on independent computations using collocation and finite elements (WG 1);
  • To derive ionosphere models (WG 1);
  • To assist the countries in establishing the geocentric datum (WG 2);
  • To assist the countries in establishing national refer-ence frames (WG 2);
  • To carry out spirit levelling of the SIRGAS 2000 and SIRGAS-CON stations (WG 2, WG 3);
  • To connect the classical vertical networks between neighbouring countries (WG 2, WG 3);
  • To adjust the geopotential numbers of the national vertical networks in a continental frame (WG 3);
  • To collaborate with the determination of the sea sur-face topography at the reference tide gauges (WG 3);
  • To establish a unified height system in the frame of a global vertical reference system (WG 3).

  • SC1.3c Regional Reference Frame for North America (NAREF)

    Co-Chairs: Richard Snay (USA), Michael Craymer (Canada)

    Terms of Reference

    To provide international focus and cooperation for issues involving the horizontal, vertical, and three-dimensional geodetic control networks of North America, including Central America, the Caribbean and Greenland (Den-mark). For more information, see http://www.naref.org.


    In collaboration with the IAG community, its service organisations and the national geodetic organizations of North America, the aims and objectives of this regional sub-commission are to provide international focus and cooperation for issues involving the horizontal, vertical and three dimensional geodetic control networks of North America. Some of these issues include:
    • Densification of the ITRF reference frame in North America and the promotion of its use;
    • Maintenance and future evolution of vertical datums (ellipsoidal and orthometric), including the North American Vertical Datum of 1888 (NAVD88) and the International Great Lakes Datum (IGLD);
    • Collocation of different measurement techniques, such as GPS, VLBI, SLR, DORIS, tide gauges, etc.;
    • Effects of crustal motion, including post-glacial rebound and tectonic motions along, e.g., the western coast of North America and in the Caribbean;
    • Standards for the accuracy of geodetic positions;
    • Outreach to the general public through focused sym-posia, articles, workshops and lectures, and technology transfer to other groups.

    • Co-Chairs
    • WG organizing committee
      Members: Michael Craymer (Canada), Per Knudsen (Denmark), Richard Snay (USA)

    Working Groups
    • SC1.3c-WG1: North American Reference Frame (NAREF)
      Chair: Michael Craymer (Canada)
    • SC1.3c-WG2: Stable North American Reference Frame (SNARF)
      Chair: Geoff Blewitt (USA)
    • SC1.3c-WG3: Reference Frame Transformations
      Chair: Michael Craymer (Canada)

    Programme of Activities
    • SC1.3c-WG1: To densify the ITRF reference frame in the North American region by organizing the computation of weekly coordinate solutions and associated accuracy information for continuously operating GPS stations that are not part of the current IGS global network. A cumulative solution of co-ordinate and velocities will also be determined on a weekly basis. The working group will organize, collect, analyse and combine solutions from individual agencies, and archive and disseminate the weekly and cumulative solutions.
    • SC1.3c-WG2: To establish a high-accuracy standard reference frame, including velocity models, procedures and transformations, tied to a “stable North America” which would serve the broad scientific and geomatics communities by providing a consistent, mm-accuracy, stable reference with which scientific and geomatics results (e.g., positioning in tectonically active areas) can be produced and compared.
    • SC1.3c-WG3: To determine consistent relationships between international, regional and national reference frames/datums, to maintain (update) these relationships as needed and to provide tools for implementing these relationships.

    SC1.3d Regional Reference Frame for Africa (AFREF)

    Chair: Richard Wonnacott (South Africa)

    Terms of Reference
    Sub-commission 1.3d (Africa) is concerned with definition and realization of a unified continental reference frame (AFREF) for Africa which will be consistent and homogeneous with the global International Terrestrial Reference Frame (ITRF).


    In collaboration with the IAG community and its services organisations and the National and Regional Mapping Organisations of Africa, the aims and objectives of Sub-commission 1.3d (Africa) are:
    • To define the continental reference system of Africa. Establish and maintain a unified geodetic reference network as the fundamental basis for the national 3-d reference networks fully consistent and homogeneous with the global reference frame of the ITRF;
    • To realize a unified vertical datum and support efforts to establish a precise African geoid, in concert with the African Geoid project activities;
    • To establish continuous, permanent GPS stations such that each nation or each user has free access to, and is at most 500 km from, such stations;
    • To provide a sustainable development environment for technology transfer, so that these activities will enhance the national networks, and numerous applications, with readily available technology;
    • To understand the necessary geodetic requirements of participating national and international agencies and;
    • To assist in establishing in-country expertise for implementation, operations, processing and analyses of modern geodetic techniques, primarily GPS.

    • Chair
    • Members of African countries

    Programme of Activities

    It is envisaged that regionalization of AFREF will follow an approach that consists of three major phases:

    1. The establishment of a framework of permanent or semi-permanent GPS base stations throughout the region that will become part of the worldwide IGS network of stations.
    2. The densification of the network of permanent or semi-permanent base stations, largely on a country-by-country basis, to determine the relationship between the national geodetic system and the ITRS, and to refine the transformation parameters necessary to relate the national systems to a common ITRF.
    3. The third and equally important phase of the project will be to address the development of a more refined geoid model for Africa and the definition of a common vertical datum for the continent. This will be done in collaboration with the IAG Africa Geoid Project (Project 2.3 Commission 2).

    It is further planned to hold workshops and seminars to strengthen the science and knowledge of geodesy and GNSS within Africa and their application to the develop-ment of reference frames.

    SC1.3e Regional Reference Frame for South-East Asia and Pacific

    Chair: Shigeru Matsuzaka (Japan)

    Terms of Reference
    To provide a regional focus for cooperation in the definition, realisation and densification of the International Terrestrial Reference frame (ITRF). This activity will be carried out in close collaboration with the Regional Geodesy Working Group of the Permanent Committee for GIS Infrastructure in Asia and the Pacific which operates under the purview of the United Nations Regional Cartographic Conference for Asia and the Pacific (UNRCC-AP).


    The objectives of the Sub-commission 1.3e are:
    • The densification of the ITRF and promotion of its use in the connection and enhancement of national networks;
    • To promote the development of a regional vertical reference datum system
    • To develop a better understanding of tectonic motions and plate boundaries within the region
    • The development of an improved geoid by enhance-ment of the data from the regional gravity network and global gravity models
    • Collocation of different measurement techniques, such as GPS, VLBI, SLR, DORIS, tide gauges, and maintenance of precise local geodetic ties at these sites.
    • To outreach to developing countries through sympo-sia, workshops, training courses, and technology transfer.
    • Encourage the establishment of further continuous GPS base stations, (accurately) positioned within ITRF, with data available both locally and to IGS.

    Program of Activities

    The activities of this sub commission will principally be carried out by the members of national surveying and mapping organisations through the PCGIAP Regional Geodesy Working Group and through the scientific members of the Asia Pacific Space Geodynamics Project (APSG).

    In order to densify the ITRF reference frame in the Asia Pacific Region an annual geodetic observation campaign will be held each year to provide an opportunity to connect to national geodetic networks and to determine site velocities. These campaigns include several geodetic techniques:
    • SLR, through cooperation with ILRS and WPLTN,
    • VLBI, through APSG,
    • GPS through PCGIAP.

    Computations are undertaken in several countries from a common data set, which includes data from weekly epoch occupations, and continuously operation GPS which are not contributing to the IGS network. Only selected stations from the massive Japanese network are included. The combination of results is being developed in the region and a PCGIAP workshop on Regional Geodesy will be held each year to strengthen regional cooperation, to discuss and analyse results of the geodetic campaigns, and to promote technology transfer.

    External Links
    • Regional Geodesy Working Group of the Permanent Committee for GIS Infrastructure in Asia and the Pacific (PCGIAP)
    • Asia Pacific Space Geodynamics project (APSG)

    SC1.3f Regional Reference Frame for Antarctica (SCAR)

    Chair: Reinhard Dietrich (Germany)

    Terms of Reference

    Sub-commission 1.3f (Antarctica) is focusing on the definition and realization of an unified reference frame for Antarctica which will be consistent with the global International Terrestrial Reference Frame (ITRF). It will establish close links to corresponding activities within the Scientific Committee on Antarctic Research (SCAR).


    • Maintenance and densification of the precise geodetic reference network in Antarctica by permanent obser-vations and GPS campaigns;
    • Realization of an unified vertical datum including GPS ties of tide gauges;
    • Providing unified reference for other GPS applications like airborne gravimetry, ground truthing for satellite missions, geodynamics and glaciology;
    • Develop technologies for remote geodetic observato-ries.

    Programme of Activities
    1. Organization of GPS campaigns in Antarctica, mainte-nance of the data archive.
    2. Data analysis and determination of the Antarctic GPS network as a regional densification of ITRF.
    3. Support airborne surveys and satellite missions with precise terrestrial reference.

    Organize meetings and workshops on Antarctic geodesy jointly with related SCAR activities in order to strengthen the international cooperation and to make optimum use of field logistics and infrastructure.

    SC 1.4 Interaction of Celestial and Terrestrial Reference Frames

    President: Harald Schuh (Austria)

    Terms of Reference

    The main objective of the IAG Sub-Commission 1.4 is the study of the interaction of the celestial and the terrestrial reference frames. In particular, SC 1.4 is focusing on the consistency between the frames.

    WG 1.4.1: Theoretical Aspects of the Celestial Reference System and Systematic Effects in the CRF Determination

    The celestial and the terrestrial ephemeris origin replaced in 2003 the vernal equinox and the traditional first axis of the terrestrial intermediate frame. Consequently, the Earth rotation angle replaced the apparent sidereal time. The Earth orientation parameters consisting of the difference between UTC and UT, the polar motion parameters, and the nutation residuals, connect the CRF and the TRF. Some effects or modelling errors which can be expressed in both frames, e.g. atmospheric gradients, can systematically affect each of the frames. Other effects affect only one frame directly but – if not modelled there correctly - can still be transcribed as deformation of the other frame or change of the Earth orientation parameters.

    In 2006 new IAU definitions were adopted with rele-vance for WG 1.4.1

    W.r.t. theory the effects of the new IAU definitions, the relation between the barycentric system (as realized by VLBI) and the geocentric system shall be studied.

    Additionally, effects which systematically affect source positions are to be identified as well as an inconsistent handling of such effects in different software packages. It is well-known that the accuracy achieved today is also limited by technique- and/or solution-related systematic biases, which are often poorly characterized or quantified.

    Concerning systematic effects, the following activities are planned:
    • Comparison of various CRF realizations
    • Study of effects of geodetic datum definition on VLBI-determined CRF
    • Study of effects of meteorological data on VLBI-determined CRF
    • Study of effects of various analysis options on VLBI-determined CRF

    WG 1.4.2: Realization of Celestial Reference Frames (CRF and Transformations)

    To achieve further progress regarding the realization of celestial reference frames it is essential to review the current status, to identify deficiencies and to make proposals for improvements. This task is closely related to various components of the IERS and the techniques analysis coordinators (in particular of the IVS), and requires a close cooperation between the different groups. The activities include the survey of the current status of CRF realization, a review regarding the implementation of IERS Conventions and IAG Fundamental Parameters and different space techniques for CRF realization.

    The International Celestial Reference Frame (ICRF) realized by VLBI is currently defined by the radio positions of 212 extragalactic objects (Ma et al. 1998). Since its inception there have been two extensions to the ICRF: ICRF-Ext.1 (IERS, 1999) and ICRF-Ext.2 (Fey et al. 2004). Planning for a second realization of the ICRF is currently underway with a projected completion date concurrent with the XXVIIth IAU General Assembly in 2009. Two Working Groups (WG) were established on the second realization of the ICRF (ICRF2) as a joint project of the International Astronomical Union (IAU), the International Earth Rotation and Reference Systems Service (IERS) and the International VLBI Service for Geodesy and Astrometry (IVS).
    Goal of the IAU WG: Oversee generation, validation and utility of ICRF2; engage in formulation of resolutions of adoption by IAU (http://rorf.usno.navy.mil/ICRF2/IAU/).

    Goal of the IVS/IERS WG: Produce ICRF2 for IERS / IVS consideration and for submission to the IAU Work-ing Group (http://www.iers.org/MainDisp.csl?pid=198-1100160 ).

    This WG (1.4.2) will survey the current status of CRF realization in close touch with the two WGs mentioned above and it will review the implementation of the IERS Conventions and IAG Fundamental Parameters concern-ing CRF relevant aspects.

    Concerning highly precise optical celestial reference frames, the state of the art optical catalogue is the FK6 (Wielen et al. 1999). It includes the FK5 and the Hipparcos-Catalogue. Upcoming optical astrometry space missions such as GAIA (Global Astrometry Inter-ferometer for Astrophysics) and SIM (Space Inter-ferometer Mission) will significantly enhance the quality of the optical catalogues in terms of position precision and number of stars.

    WG 1.4.3: Interaction Between Celestial and Terrestrial Reference Frames

    A major goal of this WG is to investigate the interaction between the celestial and terrestrial reference frame and the transformation between both (by precession, nutation, Earth rotation angle, polar motion), and to improve the consistency between celestial reference frames, a terrestrial reference frame and EOP. This includes the effect of errors in the CRF on the terrestrial reference frame and vice versa, the realization of the NNR-condition for the ITRF (e.g. the influence of deformations). The interaction between the frames and the EOP determination, the effect of various geophysical models, and the interaction with the gravity field will also be investigated.

    Transformations between corresponding reference frames can be improved connecting co-located reference points of different techniques using e.g. terrestrial local tie measurements. As it is common practice to attach GNSS receivers on LEO or other satellites used for SLR to tie the different techniques’ reference frames, such connec-tions will also be considered by the WG.

    The scheduled activities of the WG are:
    • Identify effects of errors in the CRF on the TRF and related products (e.g. EOP) and vice versa.
    • Compare the EOP with geophysical models and iden-tify the effect of Earth deformation on the EOP determination.
    • Investigate GPS satellite orbits used as quasi celestial reference frame for satellites in Low Earth Orbit.
    • Investigate satellite and receiver antenna phase centre variations and their implications to reference frame determination.

    Inter-Commission Projects

    IC-P1.2 Vertical Reference Frames

    Chair: Johannes Ihde (Germany)
    Joint with Commission 2 and IGFS)

    Terms of Reference

    The IAG Inter-commission Project 1.2 studied during the period 2003 – 2007 the possibilities of the definition and realization of a global vertical reference system (GVRS) based on the classical and modern observations and a consistent modelling of both, geometric and gravimetric parameters.

    The results of the work of the Inter-commission Project 1.2 are documented in Conventions for the Definition and Realization of a Conventional Vertical Reference System (CVRS). In the CVRS conventions a general concept for the definition and realization of a unified, global vertical reference system is described. The CVRS conventions are aligned to the IERS 2003 Conventions. Parts of the IERS 2003 conventions are the basis for the CVRS conventions.
    Open topics are the establishment of an information system describing the various regional vertical reference frames and their relation to a GVRS, the determination of transformation parameters between regional vertical reference frames and the unified global height system as well as the relationships between an GVRS and the Inter-national Terrestrial Reference System.


    • Further development of the CVRS conventions
    • Preparation of decision about numerical standards as task in cooperation with International Astronomical Union (IAU) and international hydrological associa-tions.
    • Initiation of a pilot project for an IVRS realization on the basis of the IGS TIGA-PP, GGP and IGFS for AG and a CGGM
      Program of Activities
    • Study of information on regional vertical systems and their relations to a global vertical reference system for practical applications;
    • Study of combination procedures of height data sets from different techniques;
    • Development of the basic relationships between ITRS and IVRS conventions, parameters, realization, models
    • Unification of regional (continental) height systems
    • Preparation of a pilot project for the realization of a GVRS.

    • Zuheir Altamimi (France)
    • Matt Amos (New Zealand)
    • Alireza A. Ardalan (Iran)
    • Wolfgang Bosch (Germany)
    • Claude Boucher (France)
    • Carine Bruyninx (Belgium)
    • Milan Bursa (Czech Republic)
    • Gleb Demianov (Russia)
    • Will Featherstone (Australia)
    • Rene Forsberg (Denmark)
    • Satoru Fukuda (Japan)
    • Bernhard Heck (Germany)
    • Johannes Ihde (Germany)
    • Bill Kearsley (Australia)
    • Gunter Liebsch (Germany)
    • Teixeira Luz (Brazil)
    • Markku Poutanen (Finland)
    • Laura Sanchez (Colombia)
    • Steve Shipman (UK)
    • Marc Véronneau (Canada)
    • Viliam Vatrt (Czech Republic)

    Inter-Commission Working Groups

    IC-WG 1.1 Environment Loading: Modelling for Reference Frame and positioning applications

    (Joint with Commission 4 and IERS)
    Chairs: Tonie van Dam (Luxembourg), Jim Ray (USA)

    Terms of Reference

    The accuracy and precision of current space geodetic techniques are such that displacements due to non-tidal surface mass loading are now measurable in many cases. So data analysts have increasing interest in applying displacement corrections to their geodetic results in order to remove the geophysical loading effects. Unfortunately, doing so can introduce undesirable errors into coordinate times series and thus into the ITRF itself if the corrections are not computed or applied with utmost care. Problems that are sometimes encountered include: a proliferation of different (and sometimes erroneous) loading models; use of various different reference frames not always well suited to the geodetic reductions; applying corrections at the observation level versus longer-period a-posteriori average corrections; attributes of the geophysical loading models such as a lack of mass conservation or other errors. The goal of this working group is to investigate procedures to ensure that suitable environmental corrections are available to users and that the optimal usage is made.


    The principle objectives of the scientific work are the basic research on:
    • Investigate optimal methods to mitigate loading effects in ITRF frame parameters and site coordinates

    Additional Objectives and Program of Activities
    • Accuracy assessment of the different loading models
    • Assessment of the propagation of errors into the site coordinates and the ITRF
    • Define which models should be applied at the observation level and which should be applied in the post-processing
    • Tie results/findings to IERS conventions

    • Tonie van Dam (Luxembourg)
    • Jim Ray (USA)
    • David Lavallee (UK)
    • Xavier Collilieux (France)
    • Zuheir Altamimi (France)
    • Pascal Gegout (France)
    • Ernst Schrama (Netherlands)
    • Frank Wu (USA)

    IC-WG1.2 Precise Orbit Determina-tion and reference frame definition

    (Joint with Commission 2)
    Chair: Frank Lemoine (USA)

    Terms of Reference

    The accuracy of the terrestrial reference frame terrestrial realizations is heavily dependent on the quality of the precision orbit determination (POD) to the satellites that are used for the station coordinate and EOP determinations. The POD in turn is dependent on the quality of the force and measurement models for each of the individual techniques (SLR, DORIS, GNSS) and satellites the contribute to the ITRF solutions (Lageos1, Lageos2 in the case of SLR; TOPEX/Poseidon, Jason-1, ENVISAT, The SPOT satellites in the case of DORIS, and GPS and Galileo in the case of GNSS). The activities of this working group encompass the POD issues in precision orbit determination that will affect reference frame deter-mination, and important related applications that depend on accurate reference frame such as the determination of the change in global mean sea level from space borne ocean altimeter data.


    The principle objectives of the scientific work are the basic research on:
    • Investigation of POD issues that will have a direct impact on the quality of the derived IERS products for each of the services, and assess how improvements might be made.

    Additional Objectives and Program of Activities
    • Accuracy assessment of the different ITRF realizations with respect to different POD parameterizations or satellite constellations.
    • Assessment of the impact of how improved POD might map into IERS products such as station coordinate time series and EOP determination.
    • Define which models should be applied at in the POD processing for each of the space geodetic techniques (SLR, DORIS, GNSS) .
    • Tie results/findings to IERS conventions

    • Frank Lemoine (USA)
    • Bruce Haines (USA)
    • John Ries (USA)
    • Pascal Willis (France)
    • Marek Ziebart (UK)
    • Anthony Sibthorpe (UK)
    • Gerd Gendt (Germany)
    • Jean Paul Berthias (France)

    IC-WG1.3 Concepts and termino-logy related to Geodetic Reference Systems

    Chair: Claude Boucher (France)

    Terms of Reference

    Several recent events has underlined the need to have an agreement on basic concepts related to Geodetic Reference Systems within the geodetic scientific community. This refer in particular to the work performed by IAU, presently accepted by IUGG, as well as the redaction of a new edition of the IERS Conventions. An associated ter-minological effort is needed, both within the geodetic community and outside, referring to various communities of practice, such as geo-information or GNSS community (providers or users).
    The working group will consider all needs or concerns within IAG, as well as some external structure closely connected, such as IAU or ISO.


    The global objective of the WG is to establish a report accepted by its members and describing basically a recommended nomenclature, together with all useful comments for a better reader’s understanding. An ad hoc summary will be written to be published under the IAG stamp, nominally in the Journal of Geodesy.
    The field covered are all those connected to Geodetic Reference Systems (tri-dimensional, vertical, horizontal, gravimetric, astrometric…)
    Specific steps will be followed by the WG activities:
    • Identification of topics of interest within all IAG com-ponents (commissions, services, GGOS, outreach…)
    • Selection of external bodies with relevant topic (e.g. IAU, ISO, International GNSS Committee…)
    • Effective link between the WG and the previous list
    • Selection of the rubriques of the recommended nomenclature
    • Agreement of the text of the nomenclature
    • Redaction of the final report
    • Redaction of the executive summary for the JoG

    Membership (provisional)
    • Zuheir Altamimi (France)
    • Geoff Blewitt (USA)
    • Claude Boucher (France) President
    • Nicole Capitaine (France)
    • Athanasios Dermanis (Greece)
    • Herman Drewes (Germany)
    • Johannes Ihde (Germany)
    • Sergei Klioner (Russia)
    • Erricos Pavlis (USA)
    • Gerard Petit (France)
    • Hans-Peter Plag (USA)
    • Jim Ray (USA)
    • Pascal Willis (France)

    IC-WG1.4 Site Survey and Co-locations

    (Joint with IERS)
    Chair: Gary Johnston (Australia)

    Goals and Objectives

    The major goals and objectives of the WG are:
    1. Site Survey and Standards
      • Develop, test, compare and set standards on site survey methods, including observational tech-niques, network design, classical adjustment, geo-metrical modelling and/or direct measurement tech-niques for invariant point determination, reference frame alignment, software implementation and SINEX generation. This will include the develop-ment of a standards document for undertaking site surveys;
      • Preparation and coordination of a Pilot Project (PP) on site survey. The PP will include a test cam-paign(s) to be used for the comparison of different approaches to local tie surveys addressing each of the technical elements;
      • Develop standards for the documentation of site surveys, including survey report content and format;
      • Suggest a pool of expertise to provide advice to sur-vey teams, as required, on standards for site sur-veys.
    2. Coordination
      • Liaise with local and international survey teams undertaking site surveys at important co-location sites.
      • Liaise with the technique combination groups to en-sure WG site survey products meet user require-ments;
      • Coordinate as required and make recommendations to observatories as to survey scheduling and re-survey frequency;
      • Develop and distribute software tools to the community to assist in the generation of site survey products, including SINEX generation software
      • Provide a forum to raise the profile of site survey as a critically important independent geodetic tech-nique.
    3. Site Survey Research
      • Investigate new site survey methodologies, includ-ing observational techniques, observational model-ling, invariant point definition, geometrical model-ling and/or direct measurement techniques for in-variant point determination, reference frame align-ment and structural deformation analysis.
    4. Future Planning
    5. The WG will make recommendations and prepare for the future in respect to the ongoing site survey needs of the community and how these needs will be met in the long term (to address issues outside of the scope of this WG);
    6. Develop recommendations as to how the commu-nity can provide the IERS database with all infor-mation relevant to inter-technique combination issues and to the maintenance of the ITRF: collect and archive SINEX files of local surveys with correct variance-covariance information, survey re-ports, site documentation and log files, maps, types of co-located instruments, list of site events (tech-nique independent), etc.