Satellite Laser Ranging Technologies
NASA has used satellite laser ranging (SLR) for almost two decades in the study of the earth. These include measurements of global tectonic plate motion, regional crustal deformation near plate boundaries, the Earth's gravity field, and the orientation of its polar axis and its rate of spin. The sub-centimeter precision of this technique is now attracting the attention of a new community of scientists interested in high resolution ocean, ice and land topography. The international SLR network is providing an essential link to two new oceanographic satellites, ERS-1 and TOPEX/Poseidon, which range to sea and ice surfaces using microwave altimeters.
In 1964, NASA was the first organization to successfully demonstrate laser ranging to satellites and has continued to support their development to the present. The NASA Office of Space Access and Technology (OSAT) has developed lasers, rapid detectors, and timing circuits that have become a key part of the worldwide network managed by the Goddard Space Flight Center. In satellite laser ranging, ground based stations transmit short intense laser pulses to a retroreflector equipped satellite, such as LAGEOS. The round trip time of flight of the laser pulse is precisely measured and corrected for atmospheric delay to obtain a geometric range. Ranging to these retroreflectors with a global network of laser stations allows NASA to determine both the precise orbit of a satellite and the station positions. By monitoring these stations over time, researchers can deduce the motion of the Earth-based observing sites due to plate tectonics, or other processes such as subsidence. This system is being used in precise orbit determination support of the ERS-1 and TOPEX/Poseidon missions to measure the topography of the Earth's oceans and ice sheets.
As we look to the future, OSAT is developing advanced electro-optics and laser technologies for space borne laser ranging and altimetry earth science applications. This will invert the traditional SLR system with the ranging hardware being placed onboard a satellite to range to the ground. This technology will be used on the Earth Observing System (EOS) Geoscience Laser Altimeter System (GLAS) and will measure ice sheet topography and temporal changes, cloud heights, planetary boundary heights, aerosol vertical structure, and land and water topography. An instrument based on this technology, the Mars Observer Laser Altimeter (MOLA) will fly on the Mars Global Surveyor.
For more information, contact Gordon Johnston (Gordon.Johnston@hq.nasa.gov).