The National Metrology Institute of South Africa (NMISA) recently agreed to massively improve its time reference precision in order to support the South African element of the international Square Kilometre Array (SKA) radio telescope. This agreement was embodied in a memorandum of understanding (MoU) signed with SKA South Africa (SKA SA). In terms of the MoU, the NMISA will refine its time reference by a factor of more than 1 000, from about 5 000 nanoseconds (ns) today to only about 4 ns. A nanosecond is a billionth of a second and 4 ns represents cutting-edge accuracy.

The NMISA, which falls under the Department of Trade and Industry, is responsible for the maintenance of the country’s national measurement standards, including those for time and frequency; it keeps the country’s time – South African standard time. SKA SA is the organisation responsible for South Africa’s participation in the SKA and for the country’s MeerKAT radio telescope array, which will be a precursor to the SKA. It falls under the Department of Science and Technology.

“Cutting-edge science must be based on cutting-edge measurement accuracy,” highlights NMISA Electricity and Magnetism Division director Natasha Nel-Sakharova. “One cannot claim what you cannot measure. This cooperation between the NMISA and SKA SA will enhance South Africa’s position as the best time keeping facility in Africa and make it one of the best in the world.”

“Time and frequency is a critical [factor] in the observation of celestial bodies via radio techniques,” notes SKA SA Time and Frequency Systems manager Dr Johan Burger. As both MeerKAT and the SKA are arrays of antennas, the signals from each antenna will reach the telescope data processing centre at slightly different times, because of the different distances from the antennas to the centre. These signals will have to be correlated to allow the creation of a single image. This correlation requires precise ‘time tagging’ of all of the signals. The frequencies of all the antennas have also to be precisely aligned. The final result will be a single high-resolution image.

Implementing the MoU will require the NMISA to invest in new equipment and carry out research. It will, for example, have to acquire additional caesium atomic clocks and also obtain active hydrogen maser atomic clocks. In addition, the monitoring system for these clocks will have to be improved. Further, the NMISA will have to provide the South African master clock with a steering algorithm and then upgrade this algorithm to the level required by MeerKAT and the SKA. It will necessitate research into prediction algorithms and performance management systems.

Research will also have to be done on techniques to transfer time accuracy signals from the NMISA clock room through commercial telecommunication fibres to the MeerKAT/SKA in the Karoo. This is because, when a time signal is sent through any communications system, there is a small delay before the signal reaches its destination. The extent of this delay has to be determined with great accuracy in order to use such time transfer techniques successfully. Further, this delay will have to be monitored at all times to warn of any changes in it, which could be caused by environmental factors (such as temperature) or by changes in the equipment as it ages.

These research requirements will create opportunities for African scientists and stimulate human capital development. The NMISA will cooperate with South African universities and other institutions and with metrology institutes in other countries in these research programmes. “South Africa will benefit from these technological developments as time and frequency is very important in [the] navigation of aircraft and other vehicles, defence and telecommunications,” says Burger.