New legislation for astronomy reserves in South Africa

10 December 2007

By Dr Adrian Tiplady, SKA Project Office, Johannesburg

South Africa's National Assembly has given its final approval of the South African Astronomy Geographic Advantage (AGA) Bill and it is about to be signed into law by the country's President, Mr Thabo Mbeki.

This new Act will enable the establishment of astronomy reserves that provide protection across all wavelengths, from radio through optical to gamma-ray. It allows the declaration of three types of frequency dependent protected areas:

• Core Area - encompassing the physical extent of the astronomical facility. It provides for the most stringent levels of protection required by the facility;
• Central Area - surrounding the core area. Activities that are deemed to be detrimental to the operation of the astronomy facility are prohibited as regulated;
• Co-ordination Area - surrounding the central and core area. Operators of high powered transmitters will be required to co-ordinate with the astronomical facility to ensure radio astronomy operations are not compromised by new / existing transmitters.

Figure 1 (below) illustrates a Central Area, with superimposed South African SKA configuration, that is appropriate for frequencies below 1 GHz. This Central Area is over 400 km in extent.

Figure 1: Proposed Central Area, appropriate for frequencies below 1 GHz.

It is only through the excellent co-operation and support of the major stakeholders in South Africa that the progression of the AGA Bill has been relatively smooth, and generally accepted as a necessity to protect South Africa's natural astronomical advantage.

A series of case studies are being undertaken with a number of operators of wireless communication services in the affected areas, using the proposed central zone as a basis for these discussions. These meetings sought to find feasible solutions to re-engineer existing wireless communication infrastructure to be compatible with the operation of a major radio astronomy facility, as well as prevent the establishment of further infrastructure and other activities that could be detrimental to astronomy, and in particular the SKA.

Solutions include: migration of mobile communications to frequencies beyond those used by the SKA, the use of phased array antennas for fixed transmitters and the discontinuation of high powered transmitters in favour of localised satellite downlinks and low powered repeaters.

Figure 2 indicates the signal coverage of a typical GSM base station. Following the implementation of mitigation techniques using phase array antennas, the signal is reduced by almost 50 dB in the direction of the core site, illustrated in Figure 3.

Figure 2: Coverage of GSM base station.

Figure 3: Coverage of GSM base station following implementation of mitigation techniques by GSM operator.