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In satellite laser ranging (SLR) a global network of observation stations measure the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors. This provides instantaneous range measurements of millimeter level precision which can be accumulated to provide accurate measurement of orbits and a host of important scientific data. Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ...
A satellite is an object that orbits another object (known as its primary). ...
A retroreflector is a device that sends light or other radiation back where it came from regardless of the angle of incidence, unlike a mirror, which does that only if the mirror is exactly perpendicular to the light beam. ...
Satellite laser ranging is a proven geodetic technique with significant potential for important contributions to scientific studies of the Earth/Atmosphere/Oceans system. It is the most accurate technique currently available to determine the geocentric position of an Earth satellite, allowing for the precise calibration of radar altimeters and separation of long-term instrumentation drift from secular changes in ocean topography. It has been suggested that Geodetic datum be merged into this article or section. ...
Its ability to measure the variations over time in the Earth’s gravity field and to monitor motion of the station network with respect to the geocenter, together with the capability to monitor vertical motion in an absolute system, makes it unique for modeling and evaluating long-term climate change by: The gravity field is the field of force, caused by the gravitation of the Earth, and influenced by the Earth rotation, the atmosphere and by geological bodies. ...
- Providing a reference system for post-glacial rebound, sea level and ice volume change
- Determining the temporal mass redistribution of the solid Earth, ocean, and atmosphere system
- Monitoring the response of the atmosphere to seasonal variations in solar heating.
SLR provides a unique capability for verification of the predictions of the theory of General Relativity, such as the frame-dragging effect. Changes in the elevation of Lake Superior due to glaciation and post-glacial rebound Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process...
Two-dimensional visualization of space-time distortion. ...
According to Albert Einsteins theory of general relativity, space and time get pulled out of shape near a rotating body in a phenomenon referred to as frame-dragging. ...
SLR stations form an important part of the international network of space geodetic observatories, which include VLBI, GPS, DORIS and PRARE systems. On several critical missions, SLR has provided failsafe redundancy when other radiometric tracking systems have failed. This article needs cleanup. ...
Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...
History Laser ranging to a near-Earth satellite was first carried out by NASA in 1964 with the launch of the Beacon-B satellite. Since that time, ranging precision, spurred by scientific requirements, has improved by a factor of a thousand from a few meters to a few millimeters, and more satellites equipped with retroreflectors have been launched. 1964 was a leap year starting on Wednesday (link will take you to calendar). ...
Several sets of retroreflectors were installed on the Earth's moon as part of the American Apollo and Soviet Lunokhod space programs. These retroreflectors are also ranged on a regular basis, providing a highly accurate measurement of the dynamics of the Earth/Moon system. Apollo Program insignia Project Apollo was a series of human spaceflight missions undertaken by the United States of America using the Apollo spacecraft and Saturn launch vehicle, conducted during the years 1961–1972. ...
Lunokhod (Russian for Moon walker) 1 and 2 were a pair of unmanned lunar rovers landed on the Moon by the Soviet Union. ...
During the subsequent decades, the global satellite laser ranging network has evolved into a powerful source of data for studies of the solid Earth and its ocean and atmospheric systems. In addition, SLR provides precise orbit determination for spaceborne radar altimeter missions mapping the ocean surface (which are used to model global ocean circulation), for mapping volumetric changes in continental ice masses, and for land topography. It provides a means for subnanosecond global time transfer, and a basis for special tests of the Theory of General Relativity.
The International Laser Ranging Service was formed in 1998 by the global SLR community to enhance geophysical and geodetic research activities, replacing the previous CSTG Satellite and Laser Ranging Subcommission. 1998 is a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean. ...
Uses of SLR data SLR data has provided the standard, highly accurate, long wavelength gravity field reference model which supports all precision orbit determination and provides the basis for studying temporal gravitational variations due to mass redistribution. The height of the geoid has been determined to less than ten centimeters at long wavelengths less than 1500 km. The GOCE project will measure high-accuracy gravity gradients and provide an accurate geoid model based on the Earths gravity field. ...
SLR provides mm/yr accurate determinations of tectonic drift station motion on a global scale in a geocentric reference frame. Combined with gravity models and decadal changes in Earth rotation, these results contribute to modeling of convection in the Earth’s mantle by providing constraints on related Earth interior processes. The velocity of the fiducial station in Hawaii is 70 mm./year and closely matches the rate of the background geophysical model.
See also LAGEOS, or Laser Geodynamics Satellites, are a series of scientific research satellites designed to provide an orbiting laser ranging benchmark for geodynamical studies of the Earth. ...
Lidar (light detection and ranging or laser imaging detection and ranging) is a technology that determines distance to an object or surface using laser pulses. ...
External links An early version of this article was adapted from the public domain document SATELLITE LASER RANGING AND EARTH SCIENCE at http://ilrs.gsfc.nasa.gov/docs/slrover.pdf | 
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