SA chosen as partner in worldwide study of earth during October
From 16-31 October 2002, the 26-m radio telescope at Hartebeesthoek will form
part of a global network of eight radio telescopes that will study the earth.
The eight large radio antennas will make continuous measurements for 24 hours
every day as part of an intensive campaign called CONT02.
The Hartebeesthoek Radio Astronomy Observatory (HartRAO) near Krugersdorp has
been selected as one of the eight sites that span the globe from Norway to South
Africa, and from Europe to Alaska and Hawaii. HartRAO is South Africa's national
research facility for radio astronomy and space geodesy, managed by the National
Research Foundation (NRF).
HartRAO is the only telescope in the network in the southern hemisphere. The
long north-south baselines from the northern telescopes to Hartebeesthoek are of
particular importance in improving the accuracy of the results. The radio
antennas will use the measuring technique of VLBI (very long baseline
interferometry), which receives the natural radio waves from quasars near the
edge of the visible universe. The CONT02 campaign will provide very high quality
data sets to study changes in the earth's properties on a timescale from a few
days down to a few hours.
"The study of the earth, its atmosphere and oceans, the solid ground
beneath us down to the fluid iron outer core and solid iron inner core, is
important for many reasons. These range from understanding the world we live in
to practical applications such as better weather forecasting, better navigation
of airliners, our private cars, or interplanetary spacecraft," explains Dr
Ludwig Combrinck, Leader of HartRAO's Space Geodesy Programme.
Selection of stations
"HartRAO and the other stations participating in CONT02 were selected
based on overall performance, geographic location, and their ability to operate
continuously for 15 days," says Combrinck. "The distances between the
stations must be as large as possible and they have to be well distributed over
the globe. It is also very important that the people at the stations are
committed to complete the extended scientific observations," comments
Combrinck.
The stations operate under computer control, following a pre-determined
schedule in which the telescopes point at one quasar and acquire data for a
couple of minutes, then quickly move to observe another point in a different
part of the sky.
Applications
VLBI contributes to the study of many phenomena, from general relativity and
meteorology to the properties of the innermost parts of the earth. The
applications of VLBI include climate monitoring and the measurement of sea level
change.
"The CONT02 campaign will improve our understanding of the excitation of
the solid earth by the tides and currents in the atmosphere and the oceans,
which in turn are driven by the gravity of the sun and moon and by the heating
of the earth by the sun," says Combrinck. "The length of each day
varies by micro-seconds, and over a week or longer the accumulated changes are
associated primarily with variations of the winds. There is, for example, a
strong correlation of length-of-day with the effects of El Niņo."
Technology
The measurements by VLBI require the acquisition of very large amounts of
data. Each antenna will record data at a rate of 256 million bits per second for
approximately one-third of the time, giving a total number of bits for the eight
antennas in the 15 days of about one million billion. When recorded on the
specialised high performance tape recorders, the total length of tape for each
station is about 165 km. HartRAO employs these very wide bandwidth tape
recorders.
A recent advance in the technology of VLBI is the development of disk
recording to replace tape recorders. The computer disks will reduce the cost and
improve the reliability of the recording systems - NRF.
More information:
http://www.hartrao.ac.za/news/021016cont02/cont02.html
NRF Corporate Communication and Public Relations - Hilda van Rooyen www.nrf.ac.za
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