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Satellite Laser Ranging (SLR) overview
LAGEOS satellite
Satellite Laser Ranging (SLR) targets are satellites equipped with corner cubes or retroreflectors. Currently, the global SLR network tracks over forty such satellites. The observable is the round-trip laser pulse time-of-flight to the satellite.
NGSLR at GGAO SLR and Lunar Laser Ranging (LLR) use short-pulse lasers and state-of-the-art optical receivers and timing electronics to measure the two-way time of flight (and hence distance) from ground stations to retroreflector arrays on Earth orbiting satellites and the Moon.
Earth globe The current global SLR network consists of over forty systems, several of which are managed by NASA. During the past three decades, this network has evolved into a powerful source of data for studies of the solid Earth and its ocean and atmospheric systems. This map of SLR sites is available.

The CDDIS archive of GNSS data and derived products primarily supports NASA programs and the International Laser Ranging Service (ILRS).

Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) use short-pulse lasers and state-of-the-art optical receivers and timing electronics to measure the two-way time of flight (and hence distance) from ground stations to retroreflector arrays on Earth orbiting satellites and the moon. The laser stations are also used to measure one-way distance from the ground stations to remote optical receivers on space and for very accurate time-transfer. Laser ranging activities are organized under the ILRS.

SLR is an accurate technique for determining 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. SLR’s ability to measure the temporal variations in the Earth’s gravity field and to monitor motion of a global network of stations 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.

Scientific products derived using SLR and LLR data include

  • Precise geocentric positions and motions of ground stations
  • Satellite orbits
  • Components of Earth’s gravity field and their temporal variations
  • Earth Orientation Parameters (EOP)
  • Precise lunar ephemerides
  • Information about the internal structure of the Moon

Some of the scientific results derived from SLR and LLR products include:

  • Detection and monitoring of tectonic plate motion, crustal deformation, Earth rotation, and polar motion
  • Modeling of the spatial and temporal variations of the Earth's gravitational field
  • Determination of basin-scale ocean tides
  • Monitoring of millimeter-level variations in the location of the center of mass of the total Earth system (solid Earth-atmosphere-oceans)
  • Establishment and maintenance of the International Terrestrial Reference System (ITRS)
  • Detection and monitoring of post-glacial rebound and subsidence

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.