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Report on preliminary geotechnical and tropospheric site investigation for a proposed space geodetic observatory near Matjiesfontein in the Great Karoo

Associate Director: HartRAO Space Geodesy Programme, Hartebeesthoek Radio Astronomy Observatory, P O Box 443, Krugersdorp, South Africa, 1740. (corresponding author) e-mail: ludwig{at}hartrao.ac.za

C.J.S. Fourie

Geophysicist^*– Applied Geoscience NRE Division, CSIR, South Africa, P O Box 395, Pretoria, 0001, South Africa. *Previously with Geophysics Division, Council for Geoscience., e-mail: sfourie{at}csir.co.za

L. Croukamp

Engineering Geologist – Engineering Geology Division, Council for Geoscience, South Africa, e-mail: leonc{at}geoscience.org.za, Private Bag X112, Pretoria, 0001, South Africa.

I. Saunders

Seismologist – Seismology Division, Council for Geoscience, South Africa Private Bag X112, Pretoria, 0001, South Africa. e-mail: ians{at}geoscience.org.za

The Council for Geoscience and the Hartebeesthoek Radio Astronomy Observatory (HartRAO) conducted an investigation to determine the suitability of a proposed site for a new space geodetic observatory. The proposed site is located 5 km outside Matjiesfontein in a small depression, which will shield it from radio frequency interference. The position of the site is suitable for space geodetic observations due to many cloudless days (essential for laser ranging), clear skies and low atmospheric water vapour content, which is very common in the Great Karoo. Provisionally called the International Institute for Space Geodesy and Earth Observation (IISGEO), the station is envisaged to operate advanced space geodetic techniques as part of a global network.

The proposed site is close to the geological contact between sandstones and shales of the Cape and Karoo Supergroups. Geophysical, geotechnical and atmospheric measurements were included in the survey to test the geologic structure of the site. Geophysical investigations involved magnetic, electromagnetic and seismic refraction surveys that indicated the geology of the proposed terrain is relatively homogeneous and without obvious structures such as dykes and major faults. The geotechnical investigation consisted of eight backacter test pits and a terrain evaluation. Refusal depths were between a few centimetres and 0.5 m. An atmospheric and tropospheric investigation indicated low levels of atmospheric turbulence, a prerequisite for lunar and satellite laser ranging. Data gathered indicate that the site is suitable for the proposed site development.