Hydrophone based calibrator for seawater acoustic detection of

UHE neutrinos

Omar Veledar

ACoRNE collaboration – University of Sheffield

Sapienza Universitá Di Roma25 – 27 June 2008

Outline

Rona array DAQ Calibration Pinger development Deployment Future work

Rona hydrophone array

• North-West Scotland (ranging hydrophones)• Good test bed for future deep sea experiments

• Existing infrastructure √• Wideband hydrophones √• Omnidirectionality √• Unfiltered data √• All data to shore √• Control over DAQ √• No remote access X

Rona hydrophone array

8 hydrophones Low noise preamplifiers 1200m x 200m at mid

depth in 230m deep sea Hydrophone positioning

off during data readout

DAQ

Offshore acquisition of amplified unfiltered data (16bit ADC@140kHz, ±1.2 V, 1bit = 38.147μV = 3662.1μPa)

FLAC lossless compression (>50%)

8TB RAID interfacing to

16 tape autoloader LT03

tape robot (possible to

relocate) Offline signal processing

and analysis - unlimited data re-processing

Quantum Superloader 3

Calibration - hydrophone

Acoustic detection of UHE neutrinos relies on ability to calibrate hydrophones - bipolar acoustic pulse from single omnidirectional source

Thermal energy resembling (shape and intensity) that of a neutrino induced shower should be deposited: array - interface pattern analogous to neutrino generated ‘pancake’

Other possibilities: Laser – interesting, but impractical Copper plate current discharge

Calibrator development - progressionLaboratory tank

Swimming pool

Lake (Kelk)

Open sea (Rona)

Development

Calibrator development - toolsTx – omnidirectional ± 1.8dB @ 10kHz Rx - flat frequency response

Know system and desired output to deduce required excitation pulse

Convolution integral (t)y(t) = x(t) * h(t) - complicatedConvolution (s) - freq. domain

Y(s) = X(s) . H(s)

Inverse FFTy(t) = IFFT(Y(s))

Impulse response not practical use step response

Step response = time integral of impulse response

Signal generation - system

i

invixnvnx ][][][*][

dtgftgtf )()()(*)(

0,0

0,)(

x

xx

(hydrophone)input output

system & output => excitation pulse

Time domain

Discrete time signal

Impulse

xdttxH )()(

Step

Signal generation - signal

d / dtstepHydro

system H(t)

o/pImp. resp.

Deconvolute i/p from sys. & o/pX(s) = Y(s) / H(s)

Transform to time domainx(t) = IFFT(X(s))

RECIPE Find step response (of the transmit hydrophone) Generate system TF (model transmit hydrophone) Find excitation signal by deconvoluting required o/p and system TF

Pool – hydrophone modelling

Hydrophone step response is recorded at various distances and dejittered

Hydrophone data fitting

5th order TF used to model hydrophone

TF:Mathematical representation of the relationship between the i/p and o/p of a LTI system

Technique verification

Excitation signal

Desired acoustic pulse and the estimated hydrophone driving electrical signal

Generates10 Pa @ 1m

Pool - bipolar acoustic pulse

Measured at various distances

Rona - field trip

The joys of British “Summer”

Future work

Repeat Rona deployment at different sea state and over different hydrophones using new excitation pulses

An array development using 8 hydrophones Line array – acoustic pancake

Fully autonomous for great depths Surface deployment => Power Amplifier, easy DAQ,

(linearity?)

Field data analysis

New excitation signal

Restrictive by the hydrophone linearitypotentially, can generate up to

approximately 60 Pa @ 1m

See Bevan et al. – parameterisation:more energy at core of the shower

Array hydrophone count2 hydrophones

4 hydrophones

8 hydrophones

3 hydrophones

6 hydrophones

10 hydrophones

Array development

Acquired RESON hydrophones

Developed PIC based hydrophone control

Array construction under way

Conclusions

Understood and mathematically modelled hydrophone system

Successfully generated bipolar acoustic pulses in laboratory and pool conditions

Ongoing Rona data analysis Array development Pancake detection

Thank you

Questions ?

http://pppa.group.shef.ac.uk/acorne.php