Positioning system of the ANTARES neutrino telescope

The ANTARES neutrino telescope consists of 12 string lines housing the optical detectors. Sea water currents may result in drifts for these strings by several metres from the vertical. However, muon track reconstruction is based on precise arrival time measurement of Cherenkov photons to the Optical Modules (∼1 ns) and knowledge of the Optical Module positions with respect to a fixed reference system with a corresponding resolution of ∼20 cm. lative positioning of the detector is monitored combining two systems: an acoustic system giving the 3D position of five hydrophones along the line and a set of tiltmetre–compasses giving the local tilt and orientation of each Optical Module storey. With this information, a global fit of the string shape leads to the 3D positioning of the detector within the requirements. In this paper, the positioning system is described, and the performance and results for the first years of operation in ANTARES are shown.