The Laser Retro-Reflector (LRR) was a passive optical device on board Envisat, mounted on the Earth-facing panel and close to the RA-2 antenna. It operated in the infrared, to permit ranging of the satellite by the use of Laser Tracking Stations, and therefore the accurate determination of its height.

LRR was used extensively during the commissioning phase and regularly during the mission to verify the stability of the positioning system and remained operational throughout the mission duration from 2002 to 2012. The LRR was developed by Aerospatiale (France).

LRR measurements allowed:

• calibration of the Radar Altimeter altitude measurements with an error of 10 cm
• improvement of the satellite orbit determination ensuring the production of a global ephemeris accurate to better than 1-2 m for the radial component