A versatile compact array calibrator for UHE neutrino acoustic detection

In situ acoustic calibration devices are necessary to assure the optimal performance of sensors and detectors for the acoustic detection of ultra-high energy neutrinos in underwater telescopes. Moreover, they provide evidences for the feasibility evaluation of the technique and for the determination of the entire detector efficiency. Following previous studies related to parametric acoustic sources, a first prototype of a compact acoustic array able to mimic the acoustic neutrino signal (a transient bipolar signal with ‘pancake’ directivity) is presented. The compact array developed has practical features such as easy handling and operation, and versatile functionality. In the latter sense, the transmitter is able to work in different frequency ranges for different application modes, and thus to carry out several tasks related to acoustics in underwater neutrino telescopes: emission of neutrino-like signals, calibration of sensor sensitivities and responses, emission of signals for positioning, etc. The design, construction and characterization of the prototype are described. A simulation study is also discussed, where experimental signals were propagated over distances in the kilometre range.