First results with the French Transportable Laser Ranging Station

The French Transportable Laser Ranging Station (FTLRS) is a very compact (300 kg in 8 containers) and highly mobile satellite laser ranging system (SLR) with a telescope of 13 cm diameter. It was first tested at the Observatoire de la Côte d'Azur (OCA, Grasse, France). It was of great importance to demonstrate the reliability of such a station in real field experiment. The first field campaign was carried out from October 1996 to February 1997 at the Aspretto marine base near Ajaccio on Corsica island, France. The FTLRS was set up and operational less than 2 days after arrival at the site. In 4 months, 430 satellite passes were observed including 120 of TOPEX/Poseidon (T/P). The passes were analysed using precise orbits, with those of T/P provided by CNES and GSFC/NASA especially for the mission, and have a precision of 3-4 cm. The site position was determined from the laser data with an error budget error of 1.8 cm, which has been verified with collocated measurements using the Global Positioning System (GPS). The standard deviation of the FTLRS residuals is 2 cm rms, with a bias per pass identified at the 3-5 cm level. This last aspect is under technical investigation. Since this experiment, we have made an effort to improve the detection mode of the system. Currently, the FTLRS is being modified (from IR to green wavelength, and single photo-electron detection mode) with the objective of participating in the radar altimeter calibration of Jason-1 and EnviSat (both to be launched in 2000).