Satellite Laser Ranging (SLR) is a distance measuring method with laser pulses to satellites according to the pulse-echo principle. The targets are retroreflectors at passive or active satellites, which are orbiting between 300km and 40.000km distance to Earth's surface. The satellite is tracked by the laser telescope and the time intervals of travelling laser pulses are measured.
SLR-measurements permit the determination of satellite orbits as well as the location of the SLR-telescope within a few millimetre. Satellites are orbiting the center of the mass of Earth in its gravitational field, which can be derived from SLR-measurements.
The determination of the SLR time intervals with a cesium frequency standard introduces the metric scale to the measurements, since the unit 'meter' is derived from the definition of the 'time second' defined by cesium frequency standards.
TIGO operates a 50cm-telescope for SLR-measurements with two wavelenghts: near infrared λ1=847nm and violet λ2=423.5nm. The two-color measurement permits a correction of the dispersion of the light in the atmosphere. The TIGO pico-event-timer defines the instrumental precision of 2ps, which corresponds to a light travel distance error of only 0.6mm.
The TIGO Laser Ranging System (TSLR) is operated for the International Laser Ranging Service, which coordinates the worldwide activities for the realization of a global terrestrial reference system as well as the satellite orbit determinations and predictions, calibration of altimeters, geoid determinations.