HartRAO participates in a worldwide network of Global Positioning System
(GPS) receivers known as the International GPS Service (IGS) network. All
these IGS stations provide continuous tracking using high accuracy GPS
receivers and have data transmission facilities for rapid data transmission
to various data centres. We currently have 2 permanent stations which we run
jointly with the Jet Propulsion Laboratory (JPL). One of these stations are
located at HartRAO and the other at the site of the South African
Astronomical Observatory (SAAO) close to Sutherland. Presently we are
preparing a 3rd receiver which will be stationed in Windhoek, Namibia. To
monitor local earth crust stability in southern Africa we have started to
process a regional network. This network consists of Malindi in Kenya, the
Kerguelen Islands, Ascension Islands, Gough Island, Sutherland,
Hartebeesthoek and 2 stations in Antarctica, one of which is at the new
South African Antarctic base. On a local scale we use GPS to determine the
stability of the earth's crust around HartRAO, this ensures that local scale
movements do not affect the longer global baselines.

The data from our stations are used by the IGS to generate the following
products:

(1) High accuracy GPS satellite ephemerides
(2) Earth rotation parameters
(3) Coordinates and velocities of the IGS GPS stations
(4) GPS satellite and tracking station clock information
(5) Ionospheric information
(6) Troposheric information

The accuracies of these products are sufficient to support current
scientific objectives including:

(1) Realisation of global accessibility to and the improvement of the
    International Terrestrial Reference Frame (ITRF)
(2) Monitoring deformations of the solid earth
(3) Monitoring of Earth rotation
(4) Monitoring variations in the liquid earth (sea level, ice-sheets)
(5) Scientific satellite orbit determination
(6) Ionosphere monitoring
(7) Climatological research, eventually weather prediction