Satellite Laser Ranging
Satellite Laser Ranging (SLR) as its name suggests ranges (or measures distance) to Earth orbiting satellites using a powerful laser to detect a satellite's variation from its predicted orbit. It is uniquely suited to accurately determining the variation of the Earth's centre of mass, along with the orbit parameters of satellites orbiting the Earth. Data from a global network of SLR stations are used to estimate the orbital parameters of satellites which revolve around the Earth's centre of mass. Therefore the position of the Earth's geocentre, the origin of the global reference frame, can be monitored through time. SLR has become an important geodetic instrument to be used for the establishment of an accurate global geodetic infrastructure and Earth monitoring science. SLR contributes to: the definition of the International Terrestrial Reference Frame (ITRF) by being the only space geodetic technique which defines the Earth's centre of mass. In addition, provides scale and the core network for the ITRF monitoring Earth rotation and polar motion to provide the relationship with The International Celestial Reference Frame (CRF) modelling the temporal and spatial variation of the Earth's gravity field determination of the Ocean and Earth tides monitoring tectonic plates and horizontal and vertical crustal deformation orbit determination for spaceborne altimeters and radar measurements for studies in global ocean circulation and changes in ice masses. The Geoscience Australia Lunar and Satellite Laser Ranging program began in March 1973 with the signing of a NASA-Division of National Mapping agreement under the USA-Australia Hornig Treaty for cooperation in Science.