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Metsähovi Satellite Laser Ranging (SLR)

In satellite laser ranging the positions and orbits of satellites are determined by measuring the return flight-time of very short laser pulses to the satellite. The distance of the satellite from the ground can be measured with an accuracy of few mm’s. A short laser pulse is sent by the ground station (telescope) towards the satellite equipped with retroreflectors from which the laser pulse is directly reflected back to the observing telescope.

The new SLR observatory at Metsähovi.
The new SLR observatory at Metsähovi with the 5.3m dome made by Baader GmbH (Germany). Photo: Jyri Näränen

Finnish Geospatial Research Institute has participated in the IAG Satellite Laser Ranging Service (ILRS) since 1978. The global network consists of about 40 active stations and Metsähovi is the only SLR station in the Nordic countries. SLR observations are used especially for maintenance of global reference frames and determining satellite orbits. SLR is used especially to monitor the mass-centre of the Earth in global reference systems, i.e., the origin of the global reference frame. Radar altimetry satellites and navigation satellites, including European Galileo, utilize SLR observations in orbit determination and validation. During next ten years there will be over 100 navigation satellites with reflector prisms, enhancing the need for continuous SLR measurements worldwide. Recently, SLR measurements have also been used to study space debris and transfer of accurate times over large distances.

Based on special funding from the Ministry of Agriculture and Forestry, the SLR system in Metsähovi is under renovation since 2013. This will include a new fast-moving telescope where a modern 2-kHz picosecond laser is used as the light source. A new observatory building, including a state-of-the-art observatory dome from Baader Planetarium GmbH, has been built to house the new system. Other SLR stations have similar plans to renew their systems in the near future.

Contact (

Jyri Näränen

Arttu Raja-Halli

SLR telescope
The new 50cm SLR telescope manufactured by Cybioms Corp. (US). Photo: Jyri Näränen