Network, Instrumental Improvements and Future Plans of the HartRAO Fiducial Station

Ludwig Combrinck

Hartebeesthoek Radio Astronomy Observatory

Hartebeesthoek, South Africa

June 14, WEGENER 2002, Athens-Greece

Figure 1.   MOBLAS-6 at HartRAO.

Introduction

HartRAO is currently engaged in several projects which will enhance space geodetic activities
in the southern region of the African continent. Our active role in the major space geodesy
techniques (VLBI, SLR and GPS) are set to change from passive data collection to include
active research and training. This will require transformation, capacity building and new
approaches to meet these objectives.

Our involvement in the southern African region will include specific targets and opportunities
which will elicit active and committed participation of the SADC countries, with set objectives
such as capacity building, development of local expertise and projects which will lead to
community upliftment and poverty alleviation through improved geodetic capabilities. Africa
needs to move from old mapping co-ordinate systems to the latest international standards in
order to develop frameworks for reliable geospatial information or GIS systems. This is a
prerequisite for adequate land management, cross-border management of drainage basins
and the integration of trans-national spatial information.
HartRAO is currently engaged in several projects which will enhance space geodetic activities
in the southern region of the African continent.

Current and Proposed Projects

HartRAO, as a National Facility of the National Research Foundation(NRF) is:

• 1) Establishing a regional GPS network involving all the Southern African Development Community (SADC) countries, which will be part of the envisaged African Reference Frame (AFREF) network.
• 2) Establishing a Geodetic Institute at HartRAO.
• 3) Actively involved in the IGS TIGA pilot project.
• 4) Upgrading the Geodetic VLBI antenna to enhance VLBI capabilities.
• 5) Expanding the Space Geodesy Programme to ensure adequate capacity and capability.
• 6) Planning to increase SLR tracking time to optimize data output.
• 7) Planning to build an additional radio telescope, which will allow us to increase our participation in geodetic VLBI by a factor of 3.
• 8) Committed to participate in bidding for the proposed IAG Outreach Branch

SADC Regional GPS Network

HartRAO and our collaborators are establishing a regional SADC GPS network involving all the Southern African Development Community (SADC) countries, which will be part of the envisaged African Reference Frame (AFREF) network.

The SADC consists of:

South Africa, Lesotho, Botswana, Mocambique, Swaziland, Zambia, Mauritius, Seychelles, Tanzania, Namibia, Zimbabwe, Angola, Democratic Republic of Congo (DRC) and Malawi.

The objectives of SADC include development and economic growth, promotion of self-sustaining development on the basis of collective self-reliance and to achieve complimentarity between national and regional strategies and programmes.

The ultimate objective is to build a region in which a high degree of harmonization and rationalization will enable pooling of resources to achieve collective self-reliance in order to improve the living standards of the people of the region.

Space geodesy and in particular GPS have roles to play in these objectives by facilitating the establishment of reliable geospatial information frameworks that are crucial to effective spatial planning. All geographic information systems must be based on a sound geodetic reference system.

The establishment of a regional (SADC) GPS network, as southern component is an integral part of the sustainable development programmes for the SADC region and supports the objectives of the New Partnership for Africa's Development (NEPAD) programme.

Future stations envisaged to be installed during the remainder of 2002 are:

• ZAMB:  in collaboration with NOAA and JPL (USA) was installed in Lusaka, Zambia, during March 2002.
• NAMI :  (in collaboration with GFZ Potsdam, Germany) will be installed in Windhoek (Namibia) during the latter part of 2002.
• MAWI :  (in collaboration with NRCAN, Canada) will be installed at Lilongwe in Malawi within the near future.

Similar installations are planned for the other SADC countries.

Geodetic Institute at HartRAO

The proposed Geodetic Institute at HartRAO has been accepted by the National Research Foundation (NRF) as part of our strategic plan and is fully supported by the President of the NRF. The current Space Geodesy Programme will be transformed into a Geodetic Institute located at HartRAO.

Main objectives of the GI@HartRAO will be to:

• Facilitate research, education and applications of geodesy within the African continent via student exchanges, bursaries and post-doc programmes.
• Promote the objectives of the IAG services (especially IGS, IVS and ISLRS) and facilitate access to the products of these services.
• Participate actively in global geodetic projects.
• Aid the establishment of the African Reference Frame (AFREF) by installing a permanent network of GPS stations.
• Participate in the maintenance of AFREF as an AFREF analysis and Data Center.
• Act as a training center for space geodesy.
• Increase Africa's international role and participation in global geodesy.Build capacity and capability on the continent to ensure a contribution towards sustainable development.

IGS TIGA Pilot Project

The Space Geodesy Programme is involved in monitoring the positions of tide gauges
in order to differentiate between long term sea-level changes and long term crustal changes.
This is a global project which will aid and calibrate research data used in global warming and global ocean level studies.

Main objectives of our participation in the TIGA project are:

• Establish, maintain and expand a regional continuous GPS @ Tide Gauge network
• Function as a TIGA Associate Analysis Center (TAAC).
• Function as a TIGA Data Center.

To attain these objectives we have initiated a working group "TIGA southern Africa" (TIGAsA). Amongst the participants are the SA Navy, (Hydrographic Office), Chief Directorate:Surveys and Mapping, Institute for Maritime Technology, University of Cape Town, Council for Scientific and Industrial Research , JPL (NASA).

The Map (Figure 2) below depicts TIGA Observing Stations' (TOS) data that are being archived by HartRAO for global access. More stations will be added in due time.

Figure 2. TIGAsA TOS which are archived at HartRAO.

Although at the time of writing we have installed only  two TOS stations, a further

installation at Port Nolloth, on the west coast of South Africa is being prepared

in collaboration with JPL (NASA) and the SA Navy.

Radio Telescope Upgrades

Current upgrades to the HartRAO 26 m radio telescope include:

• 1) Replacing hydraulic drive with an electric drive (completed).
• 2) Developing a new computer control and interface system based on the object oriented device control software TACO, developed and maintained by the European Synchrotron Radiation Facility (ESRF) in Grenoble, France (partially implemented).
• 4) Upgrading the antenna surface to solid panels of higher accuracy (nearly completed).
• 5) Upgrading the dichroic system which allows dual frequency operation.

These improvements will:

• 1) Extend useful life of 26m telescope.
• 2) Allow operation at up to 22GHz.
• 3) Improve efficiency at S band by a factor of 2.
• 4) Improve efficiency at X band by a factor of 1.5.
• 5) Improve signal to noise ratios.

Figure 3 provides one with a glimpse of the manufacturing of a high precision panel.  The mathematically calculated panel shape is transferred to an extremely rigid metal frame on which is located an array of bolts. These bolts are adjusted to present the exact shape that is required, with the aid of digital measuring probes. A frame is made up to accept the new panel, and using a vacuum and glue process, the panel is forced to take up the shape as set up by the array of bolts. After curing, the panel is measured again. The digital probes are interfaced to a computer to facilitate storing the measured data. This allows necessary statistics and quality control to be done. Average rms error of the panels are below 200 microns.

Figure 3. New panel on bed of bolts, glued on frame and formed by
vacuum.

Figure 4  takes one back to the start of the project (2000),  the perforated panels clearly dominate the surface. Construction of the outer ring has started. Figure 5 indicates progress towards the end of the project (2002).

Figure 4. Installation of a new panel with the aid of a 'cherry
picker'.

Figure 5. The end in sight, only the inner ring needs to be completed.

Additional Radio Telescope

HartRAO is investigating construction of an additional, more modern antenna.

Current demand for telescope time is more than twice of the available time.

To enable HartRAO to fully support the IVS, we need to construct an additional antenna for VLBI. Currently we support about 56, twenty four hour geodetic VLBI experiments per year. With an additional telescope, this could be increased by a factor of 3. The most feasible way would be to duplicate a current modern (az-el) antenna, such as the MOPRA 22m antenna.

Proposed IAG Outreach Branch

HartRAO has answered the call for participation in the IAG Outreach Branch with a proposal.

Main points of our proposal are:

The IAG outreach branch be part of the Geodetic Institute at HartRAO. Many objectives are similar or complimentary.

HartRAO would provide long term commitment, office facilities, supporting logistics as well as a real vested interest in the objectives of the Outreach Branch.

Develop membership, publish electronic newsletter.

Promote the objectives of the IAG.

Be uniquely positioned to create resource base for educators, third world countries (most are in Africa anyway) and the global community.

Viewing a global map of geodetic facilities and active research groups, Africa is highlighted by absence of IAG presence. Surely for an 'outreach' to be meaningful, you need your feet on the African continent.

Contact Information

Dr Ludwig Combrinck

Space Geodesy Programme
HartRAO
PO Box 443
Krugersdorp
South Africa

Phone: +27 12 326 0742
Fax: +27 12 326 0756

E-Mail: ludwig@hartrao.ac.za

WWW: http://hartrao.ac.za