Abstract
In the Mediterranean Sea, the KM3NeT Collaboration is constructing a the deep-sea research infrastructure hosting next generation neutrino telescopes. In the KM3NeT telescopes the Cherenkov radiation induced by the secondary charged particles produced in the interaction of cosmic and atmospheric neutrinos within an effective volume between megaton and several cubic kilometers of water are detected by an array of thousands of photomultipliers. The capability of the telescope to determine the direction of secondary charged particles and to point back to the neutrino source is strongly connected to the accuracy on photomultipliers positions. In KM3NeT, the photomultiplier positions are continuously monitored by an acoustic positioning system, designed by the KM3NeT Collaboration to reach an accuracy of the photomultiplier positions better than 20 cm.
Highlights
The construction of the KM3NeT underwater telescopes in the Mediterranean Sea has started [1]
The Cherenkov light induced by secondary charged particles is detected by an array of thousands of photomultipliers, installed in pressure-resistant glass spheres, referred to as Digital Optical Modules (DOMs), attached to flexible mooring lines anchored on the sea-bottom, called Detection Units (DUs)
In order to reconstruct the direction of the charged particles with the precision required by the scientific purposes of the KM3NeT project, the DU base positions must be georeferenced with an uncertainty of about two meters and the relative positions of the DOMs must be continuously monitored with an accuracy better than 20 cm [2]
Summary
The construction of the KM3NeT underwater telescopes in the Mediterranean Sea has started [1]. In order to reconstruct the direction of the charged particles with the precision required by the scientific purposes of the KM3NeT project, the DU base positions must be georeferenced with an uncertainty of about two meters and the relative positions of the DOMs must be continuously monitored with an accuracy better than 20 cm [2] These requirements are met through a long baseline (LBL) acoustic system composed of a number of transponders (emitter-receiver couples) installed on fixed positions on the sea-bottom and of an array of time-synchronized piezo-acoustic receivers installed inside the DOMs. Knowing the sound velocity profile along the water column and the time of flight of the acoustic pulses emitted by the LBL transponders to reach each piezo-acoustic receiver, DOM positions are calculated through multi-lateration procedures
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