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Characterization and testing of the KM3NeT acoustic positioning system

Characterization and testing of the KM3NeT acoustic positioning system. F. Simeone VLV ν T 2015 – Rome, 14/09/2015. KM3NeT Acoustic positioning system. The KM3NeT acoustic positioning system is composed of three main sub-system:

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Characterization and testing of the KM3NeT acoustic positioning system

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  1. Characterization and testing of the KM3NeT acoustic positioning system F. Simeone VLVνT 2015 – Rome, 14/09/2015

  2. KM3NeT Acoustic positioning system • The KM3NeT acoustic positioning system is composed of three main sub-system: • 1) a Long Base-Line (LBL) of acoustic transmitters (beacons) and receivers, located at known positions • 2) an array of digital acoustic receivers (DARs) installed along the detection units (DUs) of the telescope • 3) a farm of PCs for the acoustic data analysis • Beacon signals must be detectedatdistances of 1 km • Suitable frequency range 20 kHz-50 kHz • lowest level of PSD ( ~40 dB re 1 uPa2/Hz) • attenuation (0-10 dB/km) 20 kHz – 50 kHz 20 kHz – 50 kHz

  3. KM3NeT acoustic beacon The commercially available piezo-ceramic Free Flooded Rings (FFR) transducers SX30 from Sensor Tech Ltd have been chosen for LBL beacons. Each beacon can be reconfigured via a dedicated RS232 connection with a Central Logic Board (CLB) installed on the CB electronics, in order to allow reconfiguration of acoustic emission signal parameters (amplitude, waveform, timing) for “in situ” optimization of the signal detection. The signal emission trigger is synchronized with the detector master clock with calibrated time delay of 7±1 µs Signal Emitted length: from 0 to 50 ms Maximum emission amplitude: 180 dB @ 34kHz re 1 μPa at 1 m Type of acoustic signals: - Monochromatic signals configurable from 1 kHz to 80 kHz - Sine Sweep signals configurable from 1 kHz to 80 kHz - Maximum Length Sequence (MLS) signals with lengths from 5.12 ms to 40.96 ms (at 200 ksamples/s)

  4. Acoustic beacon calibration Calibration tests were performed at the water tank (dimension of 87.5 x 113 x 56.5 cm3) of Laboratory of Ultrasounds in Gandia, UPV (Department of Physics and Acoustics). Calibration Tests Capacitor Charge 5V 20V40V 60 V Horizontal position Vertical position Pressure tests were successfully performed at 400 bars in a High Pressure machine at the company Hiperbaric (Burgos)

  5. The ‘external’ Digital Acoustic Receiver Digital hydrophones are hosted on the base of the DUs and on CBs. These ‘external’ hydrophones are used to calibrate the LBL measuring the relative distances among LBL elements. The selected hydrophone is the DG0330 manufactured by Colmar s.r.l.. 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).

  6. The ‘internal’ Digital Acoustic Receiver The movement of the DUs under sea currents are monitored thanks to “internal” piezo-electric Digital Acoustic Receivers (DAR) glued from the inside to the glass sphere of each KM3NeT Digital Optical Module (DOM) The design sensitivity of the sensors is - 160 ± 6 dB re 1V/Pa at 50 kHz with a ± 3 dB variation (long time average) in the range 10 ÷ 70 kHz. Acoustic data are acquired continuously at 195 kHz, with a resolution of 24 bits. Power spectral density of the electronic noise for an internal digital acoustic receiver as measured within a DOM in the laboratory. The blue curve shows the distribution for PMTs power off, the red curve for PMTs power on.

  7. The on-shore data analysis The acoustic positioning data analysis is performed on-shore by a farm of PCs. These PCs receive, on a intranet, data from the DARs, parsed from the main data stream. The Time of Arrival (ToA ) of the acoustic signals detected by DARs are measured, analyzing the DAR raw data flow using software algorithms based on cross correlation filters. Once a LBL-beacon pulse is identified, the code associates to it the detection absolute GPS time (ToA). The distance between each beacon and each DAR will be then calculated taking into account the time of emission (ToE) of the acoustic signal and the sound velocity (SVP) along the water column. Knowing the location of the LBL beacons, each DAR position is recovered using algorithms based on spherical multi-lateration.

  8. Acoustic DAQ: latency time measurements The accuracy on the measurement of the arrival time of acoustic signals on the hydrophones depends on the accuracy of the latency time of the whole data acquisition system. The time latency of the hydrophone DAQ (including 4.5 m cable) has been measured using a dedicated setup and its value is 50.65 ± 0.02 μs for the low gain channel and 50.71 ± 0.02 μs for the high gain channel. Signal generator PPS trigger GPS receiver Clock + GPS time Analog signal (5 cycles, 20 kHz, 100 mV) Control logic board Hydrophone Hydro CH2 (low gain) Hydro CH1 (high gain)

  9. Expected performance: signal recognition Reflection Sin 20 kHz, 5 ms Direct wave Direct wave + Reflection (1 ms late) Direct wave + Reflection (1ms) 70% of the direct wave amplitude Sweep 20-21 kHz, 5 ms Reflection Direct wave Direct wave + Reflection (1ms) Direct wave + Reflection (1 ms) 70% of the direct wave amplitude

  10. Expected performance: signal recognition in ambient noise Signal amplitude: 160dB re 1uPa @1m Length signal: 5 ms Emitter – receiver distance : 1000 m Reflection (0.7 amplitude) @ 0.1 ms (~15 cm in water) Environmental noise: white noise at 40 dB re 1 uPa2/Hz (typical noise in Capo Passero site) Sin 20 kHz (1s), 22 kHz (2s), 24 kHz (3s) Sweeps 20 -21 kHz (1s ), 22-23 kHz (2s), 24 -25 kHz (3s) Xcorr (sin 20 kHz) Xcorr (sweep 20 -21 kHz) 100 entries 100 entries

  11. Expected performace : signal recognition in ambient noise Signal amplitude: 140 dB re 1uPa @1m Length signal: 5 ms Emitter – receiver distance : 1000 m Reflection (0.7 amplitude) @ 0.1 ms (~15 cm in water) Environmental noise: white noise at 40 dB re 1 uPa2/Hz (typical noise in Capo Passero site) Sin 20 kHz (1s), 22 kHz (2s), 24 kHz (3s) Sweeps 20 -21 kHz (1s ), 22-23 kHz (2s), 24 -25 kHz (3s) Xcorr (sin 20 kHz) Xcorr (sweep 20 -21 kHz) 100 entries 100 entries

  12. Conclusions • The main componenets of acoustic positioning system has been chracterized, in particular their time calibration. • The algorithms, used to recostruct the time of arrival of the becon pulses, is expected to work with good performance. • The acoustic positioning system contains innovative elements like the autocalibrating LBL that will help to reduce the systematic errors. 11

  13. Thank you

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