Co.l.mar. hydrophones for neutrino telescope
Co.l.mar. Italia supplied underwater hydrophones for the Next-Gen neutrino telescope project
KM3NeT, a future European deep-sea research infrastructure, will host a neutrino telescope with a volume of several cubic kilometres at the bottom of the Mediterranean Sea that will open a new window on the Universe.
The telescope will search for neutrinos from distant astrophysical sources like gamma ray busters, supernovae or colliding stars. It will be a powerful tool in the search for dark matter in the Universe. An array of thousands of optical sensors will detect the faint light in the deep sea from charged particles originating from collisions of the neutrinos and the Earth.
The facility will also house instrumentation from Earth and Sea sciences for long term and on-line monitoring of the deep sea environment. It works at the sea bottom at depth of several kilometers.
The selected underwater hydrophone for this project is model DG1330 engineered and manufactured by Co.l.mar. s.r.l. with cooperation of TelesubLanterna. A number of 256 hydrophones were requested.
It consists of a spherical piezo-ceramic element, read-out by an analogue board splitting the signal in two lines with different gains (+46 dB and +26 dB respectively). The two streams are sampled by a stereo 24 bit commercial ADC (Analog to Digital Converter). They are converted into AES protocol using a DIT (Digital Interface Transmitter). All the electronics is encapsulated in a hard epoxy resin molded to the cable and to the ceramic head with an additional polyurethane molding layer. An external stainless steel jacket is used for clamping the hydrophone. The power consumption is less than 100 mA @ 12 Vdc. The hydrophone is designed to accept power supply in a wider range from +9Vdc to +18 Vdc.
Two hydrophone productions are available with and without an analogue signal high-pass filtering stage. The filter frequency is 700 Hz, to reject the low frequency ambient sea-noise. The not-filtered version can be also used for acoustic noise monitoring and marine bioacoustics.
The hydrophones are delivered from the company after pressure-crush test at 400 bars (4000 m water equivalent) and shallow water calibration (sensitivity curve vs. frequency at 1 bar). A sub batch of few hydrophones will be also calibrated at high pressure (350 bars).