Commissions of Section I

Commission X   

“Global and Regional Geodetic Networks (GRGN) “

 

Report for 2000-2003

 

C. Boucher

with contributions of

 

Z. Altamimi, M. Craymer, W. Gurtner, B.G. Harsson, H. Hornik, J. Ihde, W. Kearsley, P. Knudsen, D. Milbert, R. Snay, T. Soler, J.A. Torres, M. Unis, R. Wonnacott

 

The purpose of the IAG Commission X on Global and Regional Geodetic Networks (GRGN) 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:

 

(1) Subcommissions for large geographical areas:

 

Such subcommissions will deal with all types of networks (horizontal, vertical and threedimensional) and all related projects which belong to the geographical area.

 

(2) Working Groups for specific technical topics

 

 

Several countries has appointed national representatives to the Commission. Details can be found in the Travaux de l’Association Internationale de Géodésie and Geodesist’s Handbook or in the GRGN web page.

 

Most of the activities was done in the frame of the subcommissions and some in the Working groups. The activities are presented hereafter following this structure.

 

 

 

Report on regional activities

 

 

Africa

 

(Prepared by Richard Wonnacott, South Africa and Mufta Unis, OACT)

 

The concept of unifying regional or continental geodetic references systems is not new as shown by EUREF, SIRGAS and the Asia and Pacific Regional Geodetic Project. Previously the ADOS (Africa Doppler Survey) project of the 1980's attempted to fulfill this requirement in Africa but, for various reasons, was not entirely successful. The technology at the time required that all stations be occupied simultaneously which made the implementation of the project very difficult indeed from a logistic point of view.

 

With the increased use of GNSS, and in particular GPS, the prospects of fulfilling the primary objective of unifying the geodetic datums in Africa has become much more feasible and a lot less difficult from a logistic point of view. In addition the activities and services of the IGS have improved the prospects of the successful completion of the project more feasible.

 

Broad Outline of project

The concept of AFREF is to establish a network of permanent GPS base stations at approximately 1000km spacing which will be connected to stations of the IGS including the Hartebeesthoek Radio Astronomy Observatory (HartRAO).

 

As the establishment of the primary network of base stations progresses a further break down and densification of the network will take place at the national level. The concept of unifying the vertical datums of Africa will be run in parallel and in conjunction with the Africa Geoid project. A key element in the AFREF project is that the NMO's of participating countries must be actively involved at all stages from the planning to the management and execution stages. A major difficulty lies in the lack of suitable and appropriate expertise in Africa; hence it is suggested that international experts assist in achieving the goals and objectives of AFREF but that the project must remain an African initiative. The resulting transfer of technology will enable African countries to carry out similar projects and to densify national geodetic networks to meet national requirements. The objectives of AFREF are thus:

 

  1. 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.
  2. Realize a unified vertical datum and support efforts to establish a precise African geoid, in concert with the African Geoid project activities.
  3. Establish continuous, permanent GPS stations at approximately 1000km spacing and that each nation or each user has free access to the data derived from such stations.
  4. Provide a sustainable development environment for technology transfer, so that these activities will enhance the national networks, and numerous applications, with readily available technology.
  5. Understand the necessary geodetic requirements of participating national and international agencies.
  6. Assist in establishing in-country expertise for implementation, operations, processing and analyses of modern geodetic techniques, primarily GPS.

 

There are 54 countries in Africa which will make the project extremely difficult to implement on a continental basis. For this reason it has been proposed that implementation must be at the regional level such as North (NAFREF), West (WAFREF), East (EAFREF), Central (CAFREF) and Southern (SAFREF) before the entire project can be "pulled" together to create the continental geodetic reference frame for Africa – AFREF.

 

Broad Outline of Overall Project Activities 1999 - 2003

EGS, Nice, France, April 2000

This meeting was held during the European Geophysical Society meeting held in Nice, France, in April 2000 and was called by Dr C.  Boucher, chairman of IAG Commission X  "Global and Regional Networks", also head of the ITRF and the representative of the International Earth Rotation Service (IERS) to the International GPS Service (IGS). The meeting was attended by representatives from a number of organizations including EUREF, IGS, NIMA, and Africover. Unfortunately no representatives from African countries were able to attend.

 

The meeting was called to discuss the possible organisation of a project to establish a common geodetic reference system throughout Africa (AFREF) compatible with the International Terrestrial Reference System (ITRF). The meeting also discussed ways to involve the international geodesy community to work with African nations to develop a single, uniform, continental geodetic reference system meeting international standards to replace the myriad national reference systems, many of which have not been maintained, and are out of date and inaccurate.                         

            

This meeting and earlier ad‑hoc discussions highlighted the importance of a renewed effort to realize a reference system for this continent through international collaboration directly with the African nations.  It was emphasized that this must truly be a joint effort with Africans to be successful and that it must focus on the transfer of appropriate technology to sustain the references with modern instrumentation, e.g. GPS and other satellite techniques.  It is also noted that resources will be required to enable organizational participation and project activities (e.g. travel, equipment, technical support, etc.). The meeting attendees agreed to further explore and pursue a joint project AFREF with the Africans and other international partners

 

CONSAS, Cape Town South Africa, March 2001 

During the Conference of Southern African Surveyors (CONSAS) held in Cape Town in March 2001, a meeting of the representatives of 8 Southern African countries was convened to gauge the level of interest and support for AFREF in the region. Also at the meeting were representatives from the IAG/IGS, EUREF and NIMA. The group supported the project and its goals and objectives and requested that it be organized under the auspices of the IAG. As a result of the latter request, Prof F. Sanso, the President of IAG, sent a letter of support to the represented countries urging their continued commitment to the project and offering the support and commitment of the IAG.

 

4th UN/USA GNSS Workshop, Lusaka, Zambia, July 2002

The United Nations Office for Outer Space Affairs (UNOOSA) and the United States of America co-sponsored a GNSS Applications Workshop in Lusaka Zambia in July 2002. The workshop was attended by representatives from many African and Middle Eastern countries including the IGS, US Dept of Agriculture, US Dept of Trade, ICAO and so on. One of the topics for discussion included surveying and mapping applications of GNSS. Among the resolutions resulting from the workshop a strong statement was made to create a uniform modern geodetic reference for Africa and gave the AFREF project its fullest support.

 

The outcomes of this workshop were taken forward to a final UNOOSA workshop held in Vienna in December 2002 where the outcomes of all four workshop were further worked and a final list of priority projects or actions was selected of which AFREF featured prominently.

 

RCMRD Workshop, Windhoek, Namibia, December 2002

An AFREF Planning Workshop was held in Windhoek in Namibia in December 2002. This workshop was co-sponsored by the Regional Centre for Mapping of Resources for Development (RCMRD) based in Kenya and the Surveyor General Namibia. 8 Countries from Southern and East Africa were represented as well as the United Nations Economic Commission for Africa (UNECA). There were a number of outcomes resulting from the workshop including:

 

 

Conclusion

For the period 1999 to 2003 slow but steady progress has been made with the implementation of AFREF. Africa is a large continent with many countries each with its own difficulties and priorities. It will be very difficult to get all countries involved with project from the outset but even at this early stage new countries are showing interest and the number of countries wishing to participate is growing. Of major concern is the sourcing of sufficient funding to support the project in all its stages. Of lesser concern is the comfort in knowing that the IAG and its associates and service organizations such as the IGS will give the project its fullest support.

 

Antarctica

 

A sub commission for Antarctica was established as a formal link of the SCAR activities to the GRGN. This subcommission is co-chaired by John Manning (Australia) and Reinhard Dietrich (Germany).

 

Europe

 

(Prepared by Werner Gurtner, Switzerland, Helmut Hornik, Germany and Joao Agria Torres,Portugal)

 

Introduction

The present report covers the period August 1999 – April 2003 and is focused on the following topics:

 

 

Overview and Organisation

The purpose of EUREF, the Sub-Commission for Europe of IAG’s (International Association of Geodesy) Commission X on Global and Regional Geodetic Networks, is the establishment and maintenance of the European Reference Frame. This is being achieved by means of a number of space geodetic reference stations (SLR and VLBI), an array of GPS permanent sites - the EUREF Permanent Network (EPN) -, a network of high-precision geodetic reference sites determined by various GPS campaigns, and the combination of the Unified European Levelling Network (UELN) and the European Vertical GPS Reference Network (EUVN).

 

The forum where the activities are discussed and decisions are taken is the annual symposium. The Technical Working Group (TWG) has the task to govern current activities, such as:

 

 

The TWG is composed by 19 members. It met 11 times in the period covered by this report; one more meeting is already scheduled to take place during the Toledo Symposium (June 2003). The working groups established in order to run the projects during the period 1999-2003 are the following:

 

 

It must also be mentioned the initiative to present an Expression of Interest for an Integrated Project submitted under the Framework Program 6 entitled “SCIGAL - Earth Science Applications using GALILEO”. SCIGAL aims to establish an operational European GNSS network infrastructure exploring the full potential of the GALILEO and GPS systems serving high precision users in Geodesy, Geophysics, Meteorology, Timing and Navigation, superior to the existing science-driven infrastructure for GPS, taking advantage of the expertise in GNSS data communication and analysis within the EUREF group.

 

EUREF Permanent Network (EPN)

The EUREF Permanent Network (EPN) consists presently of 137 permanent GNSS (Global Navigation Satellite System) stations. All sites have been installed following IGS standards, and about 50% of the EPN stations are also part of the IGS network. Due the enormous amount of tasks, a re-organisation of the permanent network was done in the period 2000-2001. Taking into account new technical evolutions, the EPN guidelines for the inclusion of new stations as well as for the routine operation and date flow where updated at regular intervals during the last 4 years. One of the results is that 58 % of the stations is now providing data on a near-real time basis.

 

The whole network is weekly processed on a routine basis, making use of the IGS precise orbits. Multi-year solutions of the EPN have been and will be submitted to IERS as contributions to the realisation of the International Terrestrial Reference Systems (ITRS), namely ITRF2000.

 

The EPN also runs two special projects using the installed infra-structure: ‘Monitoring of the EPN to produce coordinate time series suitable for geokinematics’ and ‘Generation of a EUREF-troposphere product’. The goal of the first one is to support the use of the EPN products for geokinematics by establishing an interface between geodesists and geophysicists. The activity involves the following basic tasks:

 

 

Within the second project tropospheric parameters are derived as part of the EPN estimation. Longer series of the zenith path delays, for example, support climate research. The basic task within this activity is to produce a combined troposphere solution with input from the individual troposphere solutions of all Analysis Centers, which contribute to the coordinate solution. Presently, the EUREF troposphere solution is recognized as the European reference solution for the troposphere and it is part of the global IGS troposphere solution.

In recognition of the growing need for European-wide improved real-time positioning and navigation, and using the recent developments in the interconnection of mobile communication and the Internet, a new EUREF initiative, the EUREF-IP Pilot Project, was set up during the last year. It aims to distribute differential GNSS data based on the EPN network.

 

Further information about the EPN can be found at http://www.epncb.oma.be.

 

Improvements and extensions of ETRS89

Besides the EPN, the establishment and maintenance of the European Reference Frame is also achieved by a network of high-precision geodetic reference sites determined by various GPS campaigns. In the last 4 years, the following campaigns have been validated by the TWG and accepted as class B standard (about 1 cm at the epoch of observation):

 

 

Three more campaigns have been already validated by the TWG as class B and are waiting for approval by the plenary at the Toledo Symposium:

 

 

Further information about the EUREF campaigns and the data base of stations can be found at http://www.geo.tudelft.nl/mgp/euref/

 

European Vertical Reference System (EVRS)

As result of the UELN and EUVN projects the IAG Sub-commission EUREF defined the European Vertical Reference System 2000 (EVRS), including a European Vertical Datum and related parameters as realisation, and for practical use as a static system. A document with the definition of EVRS was produced.

 

The UELN network is being densified and extended with new levelling observations. The existence of repeated observations in some areas presents the chance to take a first step on the way to a geokinematic height network. Some computations are being carried out in order to achieve this goal.

 

The EUVN has the objective to connect different kinds of height related observations as a contribution to a unified European height system, the European geoid determination consistent with the existing geodetic reference network EUREF/ETRS89 and the most recent realisation of UELN, and the monitoring of the sea level variations. The EUVN network consists of about 200 UELN sites observed with GPS. This project has been successfully finalised and the final report has been already published (see Publications).

 

Meanwhile, an action for the densification of the existing EUVN network (EUVN_DA) was initiated, in cooperation between EUREF and the IGGC ESc (International Gravity and Geoid Commission, European Sub-commission). The purpose is to separate gross errors in the levelling data and long wave biases in the geoid and/or levelling, at those areas where the greatest discrepancies between the current gravimetric geoid (EGG97) and the point-wise EUVN geoid have been found.

 

Further information about the European Vertical Reference System, UELN and EUVN can be found at http://evrs.leipzig.ifag.de/.

 

European Combined Geodetic Network (ECGN)

Another important issue for EUREF is to ensure the long time stability of the terrestrial reference system, including more gravity field related data in the evaluation models. So, a new project for the realisation of the European Combined Geodetic Network (ECGN) was launched.

 

The ECGN aims at the combination of geometric and gravity-related techniques for reference frame refinement, and will be developed in close cooperation with the International Gravity and Geoid Commission, European Sub-commission (IGGC Esc) of the IAG and the International Hydrographic Organisation (IHO).

 

Besides its scientific and practical implications, providing a better knowledge of the link between the geo-spatial and the vertical components, the ECGN project represents an important step ahead in the improvement of the European Reference Frame, and it is expected to be a remarkable contribution to the Integrated Global Geodetic Observing System (IGGOS) that is under development by the IAG.

 

Symposia

Following the symposium held in Prague in June 1999, three other symposia took place in Tromso (Norway) in June 2000, in Dubrovnik (Croatia) in May 2001 and Ponta Delgada (Portugal) in June 2002.

 

These meetings have been attended by more then 100 participants, representing more than 30 countries in Europe.

 

The next symposium is under preparation and will be held in Toledo (Spain) in June 2003.

 

Communication layer

A new web page has been installed at http://www.euref-iag.org. This page links to all the EUREF structures and projects. The main contents are:

 

 

In response to the interest demonstrated by the managers of the Framework Program 6, an article explaining  SCIGAL and the role of EUREF in the geo-referencing activities in Europe was published in the 29th April’s issue of the Parliament Magazine.

 

It must also be mentioned the running process for the trademark of the ‘EUREF’ name in all the European countries where this process is applicable; it is expected that the results will be presented during the Toledo Symposium.

 

External interfaces

The relationship with other organisations, the external interfaces of EUREF, has been growing. The liaison with EuroGeographics, the consortium of the National Mapping Agencies (NMA) in Europe, through its Expert Group on Geodesy (ExG-G) continues. A special reference has to be made to the financial support to EUREF for the organisation of the symposia.

 

Another result of the cooperation between EUREF and EuroGeographics is the publication of the description of national coordinate reference systems (CRS) in Europe and the transformation parameters between CRS and ETRS89 for practical purposes, following the ISO 19111 Spatial referencing by coordinates standard. This information is available at http://crs.ifag.de.

 

Presently, the cooperation has been extended to the definition of the geodetic components to be included in a project to be submitted by EuroGeographics to the INSPIRE initiative of the EU.

 

Following the initiative of the Northern African Countries to define and implement a common geodetic reference frame, EUREF was invited to participate in workshops held in TUNIS in May 2000 and Alger in 2001, in order to start a co-operation on this subject in the frame of the  AFREF initiative within Commission X.

 

Publications

The proceedings of the EUREF symposia are the main source of information concerning the EUREF activities. In the period covered by this report were published:

 

 

The proceedings of the symposium held in Ponta Delgada, 2002, are under preparation. The web page contains the papers presented at the symposia held in Tromso, Dubrovnik and Ponta Delgada. This procedure will be followed in the subsequent symposia, in order to have a faster diffusion of the information.

 

Conclusions

The Permanent Network is still developing and increasing its contribution to international projects. The GPS campaigns continued, extending and densifying the terrestrial GPS network and improving existing solutions. The EUVN project was finalised, and UELN is being densified and extended to countries in eastern Europe. Other projects have been launched (ECGN, EUVN-DA), aiming at the refinement of the existing solutions for the European Reference Frame, providing a better link between the geo-spatial and the vertical components.

 

The future situation of EUREF within the next IAG structure was also discussed, and the EUREF group looks forward to continue its activities in the frame of the new Commission I - Reference Frames.

 

The importance of the activities of EUREF is demonstrated by the involvement of more and more organisations and countries, covering almost all the map of Europe. The ETRS89 (European Terrestrial Reference System), defined more than 12 years ago, is being adopted by several countries and organisations in Europe as the official system for geo-referencing. The European Community will use ETRS89 and EVRS as conventional reference systems as well to promote widespread use as a de facto standard for future pan-European data products and services.

 

North America

 

(Prepared by Michael Craymer,Canada, Dennis Milbert, USA and Per Knudsen, Denmark)

 

Operating on a informal basis since 1997, the Sub-Commission for North America was formally created in 1999, immediately following the IUGG General Meeting in Birmingham, U.K.  The purpose of the Sub-Commission is 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 (Denmark).  Some of these issues include:

 

 

The membership of the Sub-Commission presently consists of:

 

Michael. Craymer (NRCan/GSD, Canada, co-President)

Dennis Milbert (NOAA/NGS, U.S., co-President)

Per Knudsen (KMS, Denmark)

 

No members have yet been identified for Mexico and the Caribbean, although contacts have been made with Mexico and the appointment of a representative is expected soon.

 

The members of the Sub-Commission are largely responsible for identifying the issues to be addressed and for forming working groups (WGs) to actively resolve these issues.  The follow working groups have already been created:

 

 

Most recently, a new Stable North American Reference Frame (SNARF) Working Group is being formed in collaboration with UNAVCO Inc. to develop a highly accurate, stable North American Reference Frame fixed to the North American tectonic plate.  Such a reference frame is required for the high accuracy studies of intraplate crustal motion being contemplated by, e.g., the Earthscope project ( http://www.earthscope.org/ ).

 

Activities within each of these working group are discussed below.

 

North American Reference Frame (NAREF) Working Group

 

This is the most active working group of the Sub-Commission.  The primary purpose of the WG is to densify the ITRF reference frame in the North American region by organizing the computation and combination of weekly coordinate solutions and associated accuracy information for continuously operating GPS stations that are not part of the IGS global network.  Cumulative solutions for coordinates and velocities will also be determined on a regular basis once a sufficiently long series of weekly solutions is obtained.  The WG organizes, collects, analyzes and combines solutions from individual agencies, and archives the results.  These results are available on the NAREF web site and, since mid-2002, weekly combinations are also being submitted to the IGS Global Data Centers.

 

The goals of the WG and some of it’s work have been promoted at various conferences over the past year and a half, beginning with the special session “Densification of the ITRF in North America” at the American Geophysical 2000 Spring Meeting (Craymer and Milbert, 2000; Craymer et al., 2000).  More recent results from this work group are available at www.naref.org.

 

The current contributing members of the WG are:

 

Michael Craymer (NRCan/GSD, Canada – Chairman)

Bill Dillinger (National Geodetic Survey, USA)

Mike Cline (National Geodetic Survey, USA)

Mieczyslaw Piraszewski (NRCan/GSD, Canada)

Caroline Huot (NRCan/GSD, Canada)

Brian Donahue (NRCan/GSD, Canada)

Herb Dragert (NRCan/GSC/PGC, Canada)

Scripps Institution of Oceanography (USA)

Finn Bo Madsen (KMS, Denmark)

Remi Ferland (NRCan/GSD, Canada – IGS representative)

 

These members have been active in providing regional solutions and assistance in combining them.  A plot of the current network is given in Figure 1.  The addition of the US CORS network solutions by NGS has significantly filled out the coverage and made the densification network truly North American in scope.  No success has been made thus far in soliciting weekly solutions for permanent stations in Mexico, although attempts will be made to contact some researchers in US that are computing solutions in this region for their own purposes.

 

Reference Frame Transformations Working Group

 

The purpose of this WG is to determine consistent relationships between international, regional and national reference frames/datums in North American, and to maintain (update) these relationships as needed.  The WG has been very active on an informal basis since 1997 and includes the following memebers:

 

Michael Craymer (NRCan/GSD, Canada – Chairman)

Richard Snay (NOAA/NGS, U.S.)

Tomas Soler (NOAA/NGS, U.S.)

Remi Ferland (NRCan/GSD, Canada – IGS representative)

 

The primary focus of the WG has been on maintaining the relation between the North American Datum of 1983 (NAD83) and the International Terrestrial Reference Frame (ITRF).  In fact, NAD83 has now been defined in terms of a 7 parameter Helmert transformation from ITRF96 (Craymer et al., 2000).  Transformations to/from other ITRF realizations are determined by adding the incremental transformations between ITRFs, as adopted the IERS and/or the IGS.

 

This work has unified the fundamental definition of NAD83 in both the U.S. and Canada.  Software tools have also been provide for users in both countries to make access to the NAD83 and ITRF reference frames easier than ever.

 

The North American Datum of 1983 (NAD 83) is currently defined in terms of a 14-parameter Helmert transformation from ITRF00 (Soler and Snay, 2003) in such a way that stations located within the non-deforming part of the North American plate will have little or no horizontal motion relative to this plate.  This transformation, denoted (ITRF00 --> NAD 83), equals the composition of three separate transformations

 

            (ITRF00 --> ITRF97) + (ITRF97 --> ITRF96) + (ITRF96 --> NAD 83)

 

where (ITRF00 --> ITRF97) represents the Helmert transformation from ITRF00 to ITRF97 adopted by the International Earth Rotation Service, (ITRF97 --> ITRF96) represents the Helmert transformation from ITRF97 to ITRF96 adopted by the International GPS Service, and (ITRF96 --> NAD 83) represents the Helmert transformation from ITRF96 to NAD 83 adopted by Canada and the United States (Craymer et al., 2000).

 

International Great Lakes Datum (IGLD) Working Group

 

The purpose of this working group is to consider problems related to the maintenance of the vertical datum for the management of the Great Lakes water system, including post-glacial rebound, the use of GPS/geoid techniques, lake level transfers through hydrodynamic models, comparisons with NAVD88 and the possible implementation of a revised height system.

 

The Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data recently released their report, "Apparent Vertical Movement Over the Great Lakes - Revisited," in which they documented apparent vertical motion as derived from decades of water-level data, in combination with deglaciation models (see, e.g., Mainville and Craymer, 2003). Further cooperation with this Subcommission (especially, the NAREF WG) in the area of GPS monitoring of crustal motion is expected as more GPS data is gathered for the accurate and reliable estimate of crustal movements over the region.

 

Other Activities

 

In addition to the formal activities of the Subcommission’s working groups, all countries of the Subcommission have been very active in the past couple of years maintaining and enhancing their own geodetic networks.

 

 

Figure 1:  Current NAREF densification network.  Red symbols represent IGS global solutions and green symbols the NAREF densification stations. Note that three regional densification stations in the Arctic have now become global stations.

 

 

US report

 

CORS Newtorks

More than 80 organizations in the United States have collaborated to establish the U.S. National and Cooperative Continuously Operating Reference Station (CORS) networks.  Stations typically are part of the National CORS network, the Cooperative CORS network, or both.  The National CORS network is comprised of stations whose GPS data are archived at the U.S. National Geodetic Survey.  The Cooperative CORS network is comprised of stations whose GPS data are available directly from the organization that operates the station.  A station whose GPS data are distributed both by NGS and by a cooperating organization is designated as a Combo CORS. Data and information about CORS can be obtained at: http://www.ngs.noaa.gov/CORS/

 

The National CORS currently (March 2003) contains more than 360 sites and the Cooperative CORS has over 43 sites.  Most notable among the partners is the California Spatial Reference Center (CSRC) which provides data from more than 250 CORS in California; bringing the total number of CORS to well over 600 stations.  Other organizations that distribute GPS data for Combo CORS include the International GPS Service (IGS), the Pacific Northwest Geodetic Array (PANGA), and state agencies in Florida, Ohio, Michigan, North Carolina, Pennsylvania, South Carolina, Texas, and Vermont.  A listing with web links to organizations and their GPS CORS networks is maintained at: http://www.ngs.noaa.gov/CORS/links1/

 

The CORS network also contains stations in several U.S. territories, in Central America, and in the Caribbean.  With this coverage, more than 96 percent of the coterminous United States is located within 200 km of a CORS, and more than 60 percent within 100 km. And, the CORS network is currently growing at a rate of about 6 stations per month.

 

In addition to data archival and dissemination, National CORS operations include daily coordinate solutions to quality control the GPS receiver data.  Stations in the CORS network are operated for a variety of applications, including high accuracy positioning, navigation, remote sensing, GIS development, geophysics, atmospheric science, satellite tracking, and timing.  The geophysics community is planning to install several hundred additional stations in the United States during the next few years to monitor the crustal motion associated with plate boundary interactions.  Also, organizations in Canada and the United States are collaborating to establish about 20 stations at selected water-level sites located on the Great Lakes.

 

ITRF00 Positions and Velocities

The U.S. National Geodetic Survey (NGS) delivered two separate GPS contributions towards the realization of ITRF00 in year 2000 (Marshall, 2000).  NGS has adopted ITRF00-compatible positions and velocities for all stations in the CORS network.  Approximately every year, NGS validates adopted ITRF positions and velocities for all CORS.  In particular, NGS uses every third day of CORS data in its archives to compute provisional positions and velocities for all CORS relative to the then current ITRF realization, call it ITRFxx.  If for any station, these provisional ITRFxx positional coordinates differ from the currently adopted ITRFxx positional coordinates by more than 1 cm in the north-south dimension or by more than 1 cm in the east-west dimension or by more than 2 cm in the vertical dimension, then NGS adopts the provisional position and velocity to supercede the previously adopted ITRFxx position and velocity.

 

North American Datum of 1983

In March, 2002, NGS upgraded NAD 83 positions and velocities for all CORS sites, except those located on Pacific islands, so that they equal the transformed values of recently computed ITRF00 positions and velocities. This upgrade removed inconsistencies among previously published NAD 83 positions and velocities which are detectable with modern high accuracy GPS surveys.  In addition, the NAD 83 coordinates are referred to an epoch date of 2002.00. (Previously, NAD 83 positions for the CORS sites were published for an epoch date of 1997.00). The use of the more current epoch date reduces those systematic errors occurring when points are positioned relative to CORS sites without applying appropriate site velocities. This more current epoch date benefits those involved in positioning activities in areas of crustal motion, like western CONUS and Alaska.

 

In October, 2002, NGS updated NAD 83 positions and velocities for all CORS located on Pacific islands to epoch 2002.0.  Stations on the Hawaiian Islands, the Marshall Islands, and American Samoa now refer to the spatial reference frame called NAD 83 (PACP00).  Stations on the Mariana Islands (GUAM and CNMI) now refer to the spatial reference frame called NAD 83 (MARP00).  The "datum tags", PACP00 and MARP00, indicate that adopted positions and velocities were transformed from ITRF00 positions and velocities, respectively.  Stations located in the interior of the Pacific tectonic plate are to have little or no horizontal velocity relative to NAD 83 (PACP00).   Stations located in the interior of the Mariana tectonic plate are to have little or no horizontal velocity relative to NAD 83 (MARP00).  Note that points located on Pacific islands have velocities in excess of 50 mm/yr relative to the standard NAD 83 reference frame.

 

OPUS

In 2001, NGS introduced a Web-based utility, called the Online Positioning User Service (OPUS), which will quickly and automatically calculate an accurate 3D position for a location corresponding to a user-supplied file of appropriate GPS data.  In particular, this file must contain dual-frequency carrier phase observations at a single location.  OPUS then automatically  retrieves GPS data for three suitable CORS for use in calculating the positional coordinates associated with the user-supplied data.  OPUS then emails the calculated coordinates to a user-specified email address.  The computed coordinates are provided in each of two different reference frames: NAD 83 and the pertinent ITRF realization.  For details see: http://www.ngs.noaa.gov/OPUS/

 

Network Re-Observation and Readjustment

Over the past several years the National Geodetic Survey has been re-observing the Federal Base Network (FBN) and Cooperative Base Network (CBN) to complete the ellipsoidal and orthometric height components of the FBN and CBN; see: http://www.ngs.noaa.gov/PROJECTS/FBN/

 

Project requirements for the FBN and CBN observations are to ensure 2-centimeter local accuracy in the horizontal component, as well as 2-centimeter local accuracy for the ellipsoid heights.  By the end of 2003 the observations in the 48 contiguous states and the District of Columbia should be complete.  Currently, observations for 44 states and the District of Columbia have been completed.  Of these, the vector reductions and adjustments have been completed for 39 states and the District of Columbia.  By the end of 2004 the vector reductions and adjustments for all 48 contiguous states should be complete.  At this time, a comprehensive readjustment of NAD 83 will be completed in cooperation with the Geodetic Survey Division of Canada.  Areas outside the contiguous United States (e.g., Alaska, American Samoa, Guam, Hawaii, Puerto Rico, Virgin Islands, etc,) will be included as resources permit their re-observations.

 

Comprehensive Everglades Restoration Plan

The Comprehensive Everglades Restoration Plan (CERP) is a major project to achieve ecological restoration of the Florida Everglades.  The strategy is to restore the ecology by restoring the hydrologic characteristics of the historic Everglades.  Hence, extremely accurate heights were needed to control water flow over long distances.  Beginning in 2001, NGS has been assisting the U. S. Army Corps of Engineers in a comprehensive effort to establish both leveling and GPS control for the CERP.  The leveling portion consisted of over 1500 km of new, First-Order, Class II leveling covering over 1100 bench marks in the region.  The GPS portion, completed in July 2002, consisted of a primary (1:1,000,000) network of 64 stations and a secondary (1:100,000) network of 1051 stations.  Most of the stations occupied by GPS were also bench marks from the leveling portion.  The final product is a combined GPS and optically-leveled network having ellipsoid heights with a nominal 2 cm (95%) network relative accuracy and a similar orthometric height network relative accuracy in a region of about 175 km by 175 km.  For general information on the CERP: http://www.evergladesplan.org/

 

Magnitude 7.9 Denali, Alaska Earthquake

A magnitude 7.9 earthquake occurred near Denali National Park, AK on November 3, 2002.  The geographic coordinates of the epicenter are 63.520N and 147.530W and its depth is 5.0 km. The CORS Data Analysis Team has determined 3-dimensional displacements associated with this earthquake at several CORS located in Alaska.  For details, see: http://www.ngs.noaa.gov/CORS/denali.html

 

Horizontal Time Dependent Positioning

NGS recently released version 2.7 of the HTDP (Horizontal Time-Dependent Positioning)  software (Snay, 1999) for transforming positional coordinates and/or positioning observations across time and between spatial reference frames.  Users may also apply HTDP to predict the velocities and displacements associated with crustal motion in any of several popular reference frames. 

 

Version 2.7 expands the list of permissible reference frames to include the new realization of the World Geodetic System of 1984, called WGS 84(G1150), as well as two new reference frames related to the North American Datum of 1983; one called NAD 83(PACP00) in which most points located on the Pacific tectonic plate (Hawaiian Islands, Marshall Islands, American Samoa, etc.) experience little or no horizontal velocity, the other called NAD 83(MARP00) in which most points located on the Mariana tectonic plate (Guam, Saipan, etc.) experience little or no horizontal velocity.

 

Version 2.7 incorporates a more accurate model than previous HTDP versions for the 3D displacements associated with the magnitude 7.1 Hector Mine, CA earthquake of October 16, 1999.

 

Users may execute HTDP_2.7 interactively at: http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.html     

 

One may also download the HTDP software and related information from this web site.

 

CORS Supports Crustal Motion Study

Gan and Prescott (2001) analyzed GPS data observed between 1996 and 2000 for 62 CORS distributed throughout the central and eastern United States.  Their results suggest that no significant horizontal crustal motion occurs in this part of the country, except possibly in the region encompassing that part of the Mississippi River which is located south of Illinois.  Here, points appear to be moving southward relative to the rest of the continent at an average rate of 1.7 mm/yr, with a standard deviation of 0.9 mm/yr.  While this rate is not statistically significant, the fact that the motion occurs near New Madrid, MO--where earthquake risk is considered to be high--argues that the motion may be real.

 

Canadian report

 

Recent Highlights

Geodetic Survey Division (GSD) completed another year highlighted by continued improvements to the Canadian Spatial Reference System, strengthened collaboration in global geodetic services and leadership/support for national geodetic initiatives.

 

GSD continues to be present, active, and well recognised in national and international arenas.  At the national level,  GSD relies on it’s partnership with the provincial geodetic agencies and territories through the Canadian Geodetic Reference System Committee (CGRSC) to deliver, maintain and enhance the Canadian Spatial Reference System (CSRS), including the Canada-wide Differential GPS (CDGPS) initiative, which is a primary project of the CGRSC.  GSD’s continued involvement in the GEOIDE National Centres of Excellence program has maintained the collaboration across Canada between the various universities, government departments and private companies.  Scientific collaboration with Canadian Hydrographic Service (CHS) of DFO, and Geological Surveys of Canada (GSC) also continue.

 

At the international level, GSD plays a defining role in international standards and the shape of the future of all geodetic activities. This is achieved through direct product contributions, and chairing of International Association of Geodesy (IAG) committees, working groups, special study groups, workshops, commissions, sub-commissions and others.  Canadian representation to the UN Action team on GNSS reporting to the UN Committee on Peaceful Uses of Outer Space (COPUOS) is through GSD. Other examples of international collaboration include work with GeoForschungsZentrum (GFZ) of the Republic of Germany on Sea Level change, and with the Ohio State University (OSU), National Geodetic Survey (NGS) and Forecast Systems Laboratory for water level studies in the Great Lakes region.

 

The Division is recognized as a leader and significant contributor to the International GPS Service (IGS), the International VLBI Service (IVS), the International Earth Rotation and Reference System Service (IERS), the International Gravity and Geoid Commission (IGGC), and the Global Geodynamics Project (GGP) among others.  GSD continues to be actively involved in the IAG Subcommision 10 for North America which is concentrating on developing an integrated North American Reference Frame (NAREF) solution,  and a member of a federal government working group overseeing Canada’s involvement in the European Union’s GALILEO program and continues to monitor progress of this initiative.

 

Activities continue to be consistent with the long-term strategic focus toward space-based positioning.  The following are highlights of this effort that relate to the activities of IAG Commission X.

 

International GPS Service (IGS)

GSD continues to collaborate and exchange GPS data and products from its network of Active Control Points through its many roles within the IGS, which include Analysis Centre,  Coordination for the IGS Reference Frame, and co-chair of the Real-Time Working Group, among others.  Norman Beck is also an elected member of the IGS Governing Board.

 

Global Reference Frame

Regular Very Long Baseline Interferometry (VLBI) operations continue at fiducial stations Algonquin Park Radio Observatory (ARO) and Yellowknife (YELL) as part of GSD’s contribution to the International VLBI Service (IVS), in order to relate the national and global terrestrial reference frames to the fixed Celestial reference frame.  ARO has maintained it’s designation as a primary site of the International Space Geodetic Networks of the Committee for Space Techniques in Geodesy because of it’s long history of stability, continuous operation and the multiple geodetic techniques employed, which provides scale and long term control for other techniques including GPS.

 

International VLBI Service (IVS)

Dr. Bill Petrachenko was recently elected to the IVS Governing Board.

 

Global Integration

Norman Beck has taken part in a working group tasked with implementing the charter project of the IAG called Integrated Global Geodetic Observing System, that is expected to formally kick off during IUGG this July.  Remi Ferland and Jan Kouba participated in reviewing  and charting the direction of the IERS.

 

Activities Supporting Geodynamics/Crustal Motion Studies

GSD has been collaborating with several agencies (both internationally, and nationally) on the measurement of crustal motions in various regions of Canada.

 

Together with the Ohio State University, the U.S. National Geodetic Survey and Forecast Systems Laboratory, GSD has contributed to the establishment of the Great Lakes Continuously Operating Reference Stations Network with the aim of enhancing national vertical datum monitoring, safe navigation, weather forecasting, precision farming, geodynamics, shoreline environmental monitoring and recreational boating and tourism.  For it's part, GSD has established 5 regional GPS active control points at Kingston, Port Weller, Parry Sound, Rossport and Hearst. All but the latter are co-located at CHS water level gauges.

 

Collaboration continues with Geological Surveys of Canada on the project "Relative Sea-level and Associated Climate Impacts on Northern Coasts and Seaways".  With the goal of determining relative vertical crustal motion in the western Arctic, GSD has established and operates 3 regional active control points at Inuvik, Resolute and Sachs Harbour, as well as periodically re-occupying several non-permanent stations in the region.

 

As part of another collaborative project with GSC to conduct crustal deformation measurements across Vancouver Island under the "Natural Hazards" envelope, GSD managed a special order levelling contract along a profile across Vancouver Island. 

 

Other field measurements conducted this past year for GSC included absolute gravity, and GPS at collocated sites.  Through the use of these independent observational techniques, a more accurate estimate of present-day uplift rates across the coastal margin will be determined.

 

GSD has also been collaborating with Fisheries and Oceans Canada (DFO) on the establishment of permanent GPS stations at newly established tide gauges in the Arctic as part of Canada's contribution to the international Global Ocean Observing System (GOOS), an initiative to establish an global array of tide gauges about 1000 km apart along the world's coastlines to determine long-term changes in sea level due to climate change.  GPS active control points have been co-located with tide gauges at Alert, Holman and Nain.  Two more will be established in 2003 at Qikiqtarjuaq (Baffin Island) and Tuktoyuktuk.  These GPS stations are also being contributed to the IGS GPS Tide Gauge Benchmark Monitoring (TIGA) Pilot Project, another effort to establish a global network of tide gauges co-located with permanent GPS stations. 

 

Through a tri-lateral (GSD, GFZ of Germany, and GSC Pacific ) MOU for cost-shared development of an infrastructure aimed at monitoring the vertical movement of the Earth’s crust in the broad region around Hudson Bay, six new regional GPS active control points have been established and integrated to the Active Control System network.  Results of a N-S absolute gravity survey east of James Bay were presented at the Fall AGU.  The presentation showed the correspondence of GPS-measured uplift rates with those of GSD’s JILA-2 absolute gravimeter at selected sites. 

 

Canada-Wide DGPS (CDGPS) Service

CDGPS is the CCOG sponsored initiative to broadcast GSD’s GPSoC as a means to enable GPS positioning through coordinates consistent with the Canadian Spatial Reference System.  Service Launch is scheduled for the 2003 field season.  NRCan has provided extensive engineering support to the CDGPS project to ensure the success of the project, especially as Beta Trials approach. This work included the implementation of a fully managed infrastructure for provision of GPSoC corrections to CDGPS since November 2002,  GTIS liaison for issues related to MSAT power and bandwidth,  systems management, and the implementation of a verification and validation system at MSV.  A revised Service Agreement between NRCan and GTIS reflecting the MSAT arrangement has been prepared.

 

Canadian Active Control Infrastructure

Over the past year, two new ACP sites have been established, at Fredericton, New Brunswick (FRED), and National Research Council in Ottawa, where the original site (NRC2) was decommissioned and a new site (NRC3) established.

 

GPS-C Testing

Successful testing and operational use of GPSoC was carried out by the Canadian Hydrographic Service (CHS) in the Eastern Arctic and Lake Temiscaming areas during the 2002 field season.  CHS has again requested access to GPS∑C for the 2003 season, making this their 6th year using real-time positioning for Arctic operations.

 

Canadian Base Network

The Canadian Base Network (CBN) was completed in 2000 with the addition of 6 new stations in the Arctic. This completed the Canada-wide network of 154 monuments that provide a more traditional but very high accuracy control network for further densification by individual provinces. Remeasurement of the entire network took place in 2001 and 2002 in order to monitor monument stability and to determine the effects of post-glacial rebound. Remeasurements are expected to occur on a 4-5 year basis or as needed to provide a more accurate determination of post-glacial reboud and thus more accurate, up-to-date coordinates.

 

Greenland report

 

Five geodetic permanent GPS stations are now in operation in Greenland.  The Geodetic Department of the National Survey and Cadastre of Denmark operates and maintains the stations at the Thule Airbase (THU1 and the newly established THU2) and in Scoresbysund (SCOB ).  Stations KELY and KULU in Kelyville and in Kulusuk, respectively, are operated by the University of Colorado.  The stations THU1 and KELY are included in the IGS global network.  THU2 was established in 1998 as a long-term stable station to complement the THU1 station.  THU2 is equipped with a GPS/GLONASS receiver and has contributed to the IGEX and the IGLOS campaigns.  Recently, THU2 was accepted for the IGS LEO network.  A new station in southern Greenland is being established in Julianehaab to complete the coverage in the region.

 

Activities associated with the upgrading of the geodetic network in Greenland have been going on for several years.  In 1996, the REFGR reference frame for Greenland was defined and includes eight globally positioned reference points.  Since then, GPS points have been established throughout the populated parts of Greenland.  In 2000, a special effort was made to complete this task. Sixty-seven settlements were visited and 171 new points established.  Most new points were established at old reference points so that the classic geodetic triangulation measurements can be used together with the GPS coordinates in the computation of the new coordinates.  The software for the combined adjustment of the new and the classic measurements was developed and new coordinates for most of the ice free parts of Greenland have been computed during 2001.

 

References

Craymer, M. and M. Piraszewski (2002) Canadian Contributions to the NAREF Initiative to Densify the ITRF in North America.  AGU 2002 Fall Meeting, San Francisco, December 6-10.

 

Craymer, M. and M. Piraszewski (2002) Densification of the ITRF: The NAREF Experience in North America.  IGS Network, Data and Analysis Center Workshop, Ottawa, April 8-11.

 

Craymer, M., M. Piraszewski and C. Huot (2002) Current Status to Densify the ITRF in North America.  IGS Network, Data and Analysis Center Workshop, Ottawa, April 8-11.

 

Craymer, M.R.  The North American Reference Frame (2002) Densification of the ITRF in North America. Plate Boundary Observatory US/Canada Workshop, Seattle, March 5.

 

Craymer, M.R. and M. Piraszewski (2001) The NAREF Initiative to Densify the ITRF in North America. IAG 2001 Scientific Assembly, Budapest, Hungary, September 2-7.

 

Craymer, M.R. and M. Piraszewski (2001) The North American Reference Frame (NAREF): An Initiative to Densify the ITRF in North America. Proceedings of KIS 2001: International Symposium on Kinematic Systems in Geodesy, Geomatics and Navigation, Banff, Canada, June 5-8, 2001. Revised July 13.

 

Craymer, M.R. and M. Piraszewski (2001) The North American Reference Frame (NAREF): An Initiative to Densify the ITRF in North America.  KIS 2001: International Symposium on Kinematic Systems in Geodesy, Geomatics and Navigation, Banff, Canada, June 5-8.

 

Craymer, M.R. and M. Piraszewski (2001) The NAREF Initiative to Densify the ITRF in North America. Proceedings of the EUREF Permanent Network Third Local Analysis Centres Workshop, Warsaw University of Technology, Warsaw, Poland, May 31 - June 1.

 

Craymer, M.R., R. Ferland, R. Snay (2000) Realization and Unification of NAD83 in Canada and the US via the ITRF.  In R. Rummel, H. Drewes, W. Bosch, H. Hornik (eds.), Towards an Integrated Global Geodetic Observing System (IGGOS), IAG Section II Symposium, Munich, October 5-9, 1998.  International Association of Geodesy Symposia, Volume 120, Springer-Verlag, Berlin.

 

Craymer, M.R., D. Milbert (2000).  NAREF: Densification of the ITRF in North America.  IGS Analysis Center Workshop, Washington, September 25-29.

 

Craymer, M.R., M. Piraszewski, C. Huot (2000) Canadian Regional Solutions for NAREF:  Initial Results.  Presented at the AGU 2000 Spring Meeting, Washington, June 3.

 

Craymer, M.R., M. Piraszewski (2001a) The NAREF Initiative to Densify the ITRF in North America.  Presented at the CGU Annual Scientific Meeting, Ottawa, May 14-17.

 

Craymer, M.R. and M. Piraszewski (2001b). The NAREF Initiative to Densify the ITRF in North America. Proceedings of the EUREF Permanent Network Third Local Analysis Centres Workshop, Warsaw University of Technology, Warsaw, Poland, May 31 - June 1.

 

Craymer, M.R. and M. Piraszewski (2001c). The North American Reference Frame (NAREF): An Initiative to Densify the ITRF in North America. Proceedings of KIS 2001: International Symposium on Kinematic Systems in Geodesy, Geomatics and Navigation, Banff, Canada, June 5-8. Revised July 13.

 

Eckl, R. Snay, T. Soler, M. Cline, and G. Mader (2001) Accuracy of GPS-Derived Relative Positions as a Function of Interstation Distance and Observing-Session Duration,  Journal of Geodesy, vol 75, 633-640.

 

Ferland R., Z. Altamimi, C. Bruyninx, M. Craymer, H. Habrich and J. Kouba (2002) Regional Networks Densification.  Proceedings of the IGS Network, Data and Analysis Center Workshop, Ottawa, April 8-11.

 

Gan, W., and WH Prescott (2001) Crustal deformation rates in central and eastern U.S. inferred from GPS, Geophysical Research Letters, 28, 3733-3736.

 

Henton, J., M.R. Craymer, J.O. Liard, T.S. James, C. Gagnon and E. Lapelle (2002) Absolute Gravity and GPS Measurements of Uplift in the James Bay Region, Quebec, Canada.  AGU 2002 Fall Meeting, San Francisco, December 6-10.

 

Mader, G and F Czopak (2002) The Block IIA Satellites: Calibrating Antenna Phase Centers. GPS World, 13(5), 40-46.

 

Mader, G.L. & M.L. Morrison (2002). Using Interpolation and Extrapolation Techniques to Yield High Data Rates and Ionosphere Delay Estimates from Continuously Operating GPS networks, Proc. ION-GPS 2002, Portland, OR, September 24-27, 2342-2348.

 

Mainville, A. and M.R. Craymer (2003) Present-day tilting of the Great Lakes region based on water level gauges.  Submitted to Geological Society of America Bulletin.

 

Marshall, J (2000) Estimating North American CORS coordinates in a consistent fashion within the framework of a global solution, Spring 2000 American Geophysical Union Conference, Washington, D.C.

 

Marshall, J., M. Schenewerk, R. Snay, and S. Gutman (2001) The Effect of the MAPS Weather Model on GPS-Derived Ellipsoidal Heights, GPS Solutions, Vol 5, pp 1-14.

 

Mazzotti, S., P. Flueck, R.D. Hyndman, H. Dragert, M. Craymer, M. Schmidt (2002) Tectonics of Western Canada From GPS Observations.  AGU 2002 Fall Meeting, San Francisco, December 6-10.

 

Milbert, D. and M. Craymer (2000) NAREF:  An Initiative to Densify the ITRF in North America.  AGU 2000 Spring Meeting, Washington, DC, 3 June.

 

Piraszewski, M., M. Craymer and C. Huot (2000) Preliminary Results of the NAREF Densification. International GPS Service (IGS) Analysis Center Workshop, U.S. Naval Observatory, Washington, DC, 25-29 September.

 

Prusky, J. (2001). The Cooperative CORS Program, Professional Surveyor, 21(1), 14, 16, 22.

 

Schenewerk, M., J. Marshall, W. Dillinger, and N. Weston (1999)  Vertical ocean loading deformations derived from a global GPS network, EOS, Trans., Amer. Geophys. Union, 80(46), 262.

 

Schenewerk, M.J., J. Marshall & W. Dillinger (2001). Vertical ocean-loading deformation derived from a global GPS network, J. Geodetic Soc. of Japan, 47(1).

 

Sella, GF, TH Dixon, and A. Mao (2002) REVEL: A model for Recent plate velocities from space geodesy, Journal of Geophysical Research, 107, ETG 11, 1-30.

 

Snay, R (1999) Using the HTDP software to transform spatial coordinates across time and between reference frames, Surveying and Land Information Systems, 59, 15-25.

 

Snay, RA (2003) Introducing two spatial reference frames for regions of the Pacific Ocean, Surveying and Land Information Science, in press.

 

Snay, R., M. Chin, D. Conner, T. Soler, C. Zervas, J. Oyler, M. Craymer, S.I. Gutman, C.K. Shum, K.-C. Cheng and C.-Y. Kuo (2002) Great Lakes Continuous GPS (CGPS) Network For Geodynamics, Meteorology and Safe Navigation. Weikko A. Heiskanen Symposium in Geodesy, The Ohio State University, Columbus, OH, October 1-4.

 

Snay, R.A. and T. Soler (1999). Part 1 - Modern Terrestrial Reference Systems. Professional Surveyor, 19(10), 32-33.

 

Snay, R.A. and T. Soler (2000). Part 2 - The evolution of NAD83. Professional Surveyor, 20(2), 16, 18.

 

Snay, R.A. and T. Soler (2000). Part 3 - WGS 84 and ITRS. Professional Surveyor, 20(3), 24, 26, 28.

 

Snay, R.A. and T. Soler (2000). Part 4 - Practical considerations for accurate positioning. Professional Surveyor, 20(4), 32-34.

 

Snay, R.A., T. Soler and M. Eckl (2002). GPS precision with carrier phase observations: Does distance and/or time matter?, Professional Surveyor, 22(10), 20, 22, 24.

 

Snay, R., G. Adams, M. Chin, S. Frakes, T. Soler and N. Weston (2002). The synergistic CORS program continues to evolve, Proc. ION-GPS 2002, Portland, OR, September 24-27, 2630-2639.

 

Soler, T. (2001). Densifying 3D GPS networks by accurate transformation of vector components, GPS Solutions, 4(3), 27-33.

 

Soler, T., R.E. Johnson, L.F. Thormahlen, R.H. Foote (2001). Parting the waters of the Western Gap: The U.S./Mexico Coastline Survey, GPS World, 12(5), 28-30, 33.

 

Soler, T. (2001). Transformaciones rigurosas de vectores GPS al marco de referencia SIRGAS, Revista Cartográfica, 72(1), 139-147.

 

Soler, T., N.D. Weston, H. Han (2002). Computing NAD 83 coordinates using ITRF-derived vector components, Proceedings XII FIG International Congress, ACSM/ASPRS Annual Conferences, April 19-26, Washington, D.C.

 

Soler, T., J. Marshall (2002). Rigorous transformation of variance-covariance matrices of GPS-derived coordinates and velocities, GPS Solutions, 6(1-2), 76-90.

 

Soler, T., R.A. Snay (2003). Equations for transforming positions and velocities between ITRF00 and NAD 83, J. Surveying Engineering, ASCE, in press.

 

Soler, T., J. Marshall (2003). A note on frame transformations with applications to geodetic

datums, GPS Solutions, in press.

 

Soler, T., R.H. Foote, D. Hoyle and V. Bocean (2000). Accurate GPS orientation of a long baseline for neutrino oscillation experiments at Fermilab, Geophysical Research Letters, 27(23), 3921-3924.

 

Vanicek, P., M.R. Craymer and E.J. Krakiwsky (2001) Robustness Analysis of Geodetic Horizontal Networks.  Journal of Geodesy, 75(4).

 

Vaníc˘ek, P., P. Novak, M. Craymer and S. Pagiatakis (2002) On the Correct Determination of Transformation Parameters of a Horizontal Geodetic Datum.  Geomatica, Vol. 56, No. 4.

 

 

South America

 

South America is very well covered by the SIRGAS project, for which Hermann Drewes (Germany) acted as liaison to GRGN. See references for further informations.

 

South East Asia and Pacific

 

This is a report to Commission X on Geodetic activities in the Asia Pacific from the Sub Commission on SE Asia which was reformed in 1998 with John Manning (Australia) and Junyong Chen (China) as co-chairs.

International cooperation in Geodesy at the national level is coordinated through the Regional Geodetic Networks Working Group of the Permanent Committee for GIS Infrastructure in the Asia Pacific (PCGIAP)

As the objectives of Commission X are close to the aims of the Regional Geodetic Networks Working Group it was sensible to reform the sub commission from Working Group representatives.

 

 

 

Report of Commission X Working groups

 

Working Group 1 on Datums and Coordinate Systems

 

(Prepared by Bjorn Geirr Harsson, Norway and Johannes Ihde, Germany)

 

The Working Group Datum and Coordinate systems has mainly been done its activities in relation to ISO standards. In January 2003 the standard ISO 19111, Geographic information ― Spatial referencing by coordinates was accepted as an international standard. This standard defines the conceptual schema for the description of spatial referencing by coordinates. A coordinate reference system is defined by one datum and by one coordinate system. The standard describes the minimum data required to define one-, two- and three-dimensional coordinate reference systems. It allows additional descriptive information to be provided. It also describes the information required to change coordinate values from one coordinate reference system to another. A set of coordinates on the same coordinate reference system requires one coordinate reference system description.

In addition to describing a coordinate reference system, this standard provides for the description of a coordinate transformation or coordinate conversion between two different coordinate reference systems. With such information, geographic data referred to different coordinate reference systems can be merged together for integrated manipulation.

In the standard 33 geodesy related terms are defined.

 

Another standard is under preparation, ISO 19127, Geographic information/Geomatics - Geodetic Codes and Parameters. This standard provides for creation and maintenance of a publicly available list of geodetic codes and parameters that is in compliance with ISO 19111, and that provides guidance on applicability and appropriate use. It provides guidance for proposals for additions or modifications to the list, validation of proposals, inclusion of data, and maintenance.

 

 

With the Spatial Reference Workshop 1999 and the Cartographic Projection Workshop 2000 in Marne-la-Vallee the foundations were laid for the definition of uniform European coordinate reference systems in position and height for the spatial referencing of geo-data of the European Commission and for future specifications of products to be delivered to the EC and the promotion of wider use of the system within all member states by appropriate means. The information system for coordinate reference systems (CRS) is a common initiative of EUREF and EuroGeographics (http://crs.ifag.de). The CRS information system orientates on the international standard ISO 19111. The Information System contains at present: The descriptions of pan-European Coordinate Reference Systems, the descriptions of national Coordinate Reference Systems of European countries and the descriptions of transformations to European Terrestrial Reference System ETRS89.

 

 

 

Working Group 3 on the Worldwide Unification of Vertical Datums

 

(Prepared by H. W. Kearsley, Australia)

 

The Goal

To investigate the possible actions to be undertaken to realize a global vertical datum, and to determine its connection to various existing vertical datums.

 

Significance

To bring the many height-related data sets around the globe onto the one common reference surface - the global geoid;

To enable the scientific study of departures of the regional vertical datums (both inter-regional and intra-regional) from the global geoid;

To ensure all height-related data, and results derived therefrom, relate to the global geoid. For example, to ensure that gravity reductions or terrain effects for global geopotential models based upon national height datums relate to the common global geoid.

To assist the study of distortions in the National Height Datums, and the study of oceanographic phenomena (SST) at tide gauges.

 

Corresponding contributors and contacts

DENNIS@NGS.NOAA.GOV  davez@ngs.noaa.gov  DENKER@ife.uni-hannover.de  deni@lsi.usp.br  dru@NGS.NOAA.GOV erich.gubler@se254.lt.admin.ch fortes@deged.igbe.gov.br  geoide@ipmtf4.topo.polimi.it  hornik@dgfi.badw-muenchen.de  ISZAHD@isn1.iessg.nottingham.ac.uk  JADAM@epito.bme.hu  jimsteed@auslig.gov.au  lhothem@usgs.gov  matt.higgins@mailbox.uq.edu.au  plw@pol.ac.uk  pxu@triton.geo.bosai.go.jp  RHRAPP@OHSTMVSA.ACS.OHIO-STATE.EDU  KumarM@nima.mil  rf@KMS.MIN.DK  sideris@acs.ucalgary.ca  schlueter@wettzell.ifag.de  TFEATHER@alpha2.curtin.edu.au   tfb@pol.ac.uk

 

Meetings

1 IAG, Rio (Sept, 1997)

After an informal meeting of the Working Group in IAG, Rio, the following email was circulated:

Those of you who I originally circulated will remember my proposal to adopt a system for this purpose (for those not on the original circulation list, I have included this original proposal at the end of this email.) I was told that it was NOT possible to propose any resolution such as the one below at the IAG meeting in Rio. In any case, at the informal meeting of some members of the working group, it was felt to do this would be premature. Instead, it was proposed that

 

               I.      (say) four study groups be set up to carry out research into the operational and theoretical aspects of vertical datum connections,

             II.      using selected regions for pilot studies. Such regions would include those which already had extensive experience in datum unification, eg EUVN for Europe, NAVD for Nth America; and those areas where there were or are to be extensive regional high-precision GPS campaigns (eg SIRGAS - Sth America, and the Asia-Pacific Space Geodynamics Project (APSG - Pacific and SE Asia; or its subset GEODYSSEA)),

            III.      that the results be presented in 2 years at the IUGG in the Birmingham, UK meeting, commenting on such matters as

a)       preferred height systems

b)       preferred geometric reference

c)       preferred tide model, and

d)       preferred geopotential model.

 

This can be used as the basis for a resolution at IUGG which proposes the method to be used in the unification of the vertical datums.

 

Comments:

 

               I.      A meeting of the Regional Geodetic Network Working Group was held between the dates of 2-4 July 1998 in Canberra Australia, hosted by AUSLIG. A this meeting a number of important objectives and strategies directly related to the vertical datum unification were devised (see http://www.gmat.unsw.edu.au/final_year_thesis/p_epstein/campag.htm )

             II.      Unfortunately there is no special session specifically set aside at IUGG 1999 for the discussion of the matters above. However, a number of papers touching on these matters are being presented at session G6.

 

2. IERS Workshop, Paris, 14 -18 October, 1996

A meeting entitled Vertical References, and chaired by C. Boucher and W. E. Carter, produced a very useful report canvassing various theoretical and practical impediments to the realization of a unified vertical datum. It also made four recommendations specifically dealing with this problem, addressing both housekeeping and operational matters to overcome these difficulties (IERS 1997, Technical Note No 22).

 

World Wide Web Page

A summary of recent developments, the problems of unification, recent papers, and links to other relevant scientific groups and campaigns (eg EUVN, NAVD) is now available at HYPERLINK http://www.gmat.unsw.edu.au/final_year_thesis/p_epstein/main.htm .

 

Conclusions

 

We can conclude that the topic of the GRGN commission has shown during the last quadriennium a tremendous development of activities, in particular on

 

 

 

We  hope that GRGN has played a role of stimulation and coordination by helping the dissemination of information, standardization, cooperation and education. We can also appreciate that the regional cooperation is active almost everywhere.

 

IAG has adopted a new structure in which the GRGN actiivities will obviously continue, especially in the new Commissions 1 and 4.