Download ACoRNE Status Report

Amplitude calibration
Amplitude Calibration with
Acoustic Transducers
Jonathan Perkin - University of Sheffield
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
Amplitude calibration
Contents
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Introduction: The calibration problem
The ideal calibration tool
Single source emitter
Hydrophone modelling
Laboratory results so far
Proposed deployment in the field
Linear phased array
Understanding the environment
Summary
2007…
Deep inelastic scattering, with the sea as your
calorimeter…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
neutrino
Sea/Ice/Salt
Hydrophone
Array
Acoustic
Pressure
Waves
Pressure (Pa)
100
Jonathan Perkin
10-3
-5
Amplitude calibration
The problem of amplitude calibration
for acoustic neutrino telescopes
• In order to successfully undertake
astronomy via the acoustic
detection of UHE neutrinos it is
essential that we can reconstruct
its trajectory and its energy
• Therefore one must have some
facility with which to calibrate
Far field Radiation pattern hydrophones w.r.t to the energy
of a given interaction
• The problem posed is that there
is no natural background
against which calibration can be
performed (c.f atmospheric
muons in other particle
detectors)…
2007…
Angle (degrees)
5
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
• The ideal calibration device for an acoustic detector will produce a
thermoacoustic emission identical to that emitted by the hadronic
cascade resulting from a UHE neutrino interacting in the sea
•
We have already seen that proton
induced showers produce equivalent
energy deposition to neutrino
induced showers - however it may be
impractical to put a proton
accelerator 2km deep in the sea
T.Karg
Arena2005
The principle of thermoacoustic emission
from lasers has been proven in the
laboratory - it would be advantageous if this
can be done in the field
Jonathan Perkin
SUD Catania 07
Amplitude calibration
The ‘ideal’ calibrator
2007…
Acoustic Cosmic Ray Neutrino Experiment
Short duration laser pulses → energy deposition at any given
point is a delta function in time
Path length limited by reflecting element? →
angular spread of the acoustic pulse mimics that of
the shower
Extra (de)focussing optics to
control lateral spread of the energy
deposit → ensures the pulse shape
and frequency spectrum mimic that
of a shower
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Jonathan Perkin
PAPV counter optical system
Powerful laser pulse (1.5 J at
1060nm or 0.2J 530 nm)
operates at ranges from 300 to
1,500 metres - deployable?
SUD Catania 07
Amplitude calibration
Calibration with lasers?
2007…
Acoustic Cosmic Ray Neutrino Experiment
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Can use electrical theory to model piezo electric effect in piezoceramics
Characterise the transfer function (TF) of a hydrophone using known
inputs such that the required input for a given desired output can be
determined [O.Veledar, S.Danaher]
1. Apply known signal (e.g. step)
2. From step response determine transfer function (increase order of
model to find best fit) [RC circuit model represents transfer function]
3. From transfer function can determine impulse response (IR)
4. We want to determine the input u required to generate a bipolar
output (dGaus)
5. u = IFFT[ FFT(dGaus) / FFT(IR) ]
Amplitude calibration
Single source emitter
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
• 5th order RC circuit model used to characterise
hydrophone via the equivalent circuit technique
Vin - Vc
= IC
R
Ic
Vin
I = IR - IC
Omnidirectional
emitter in breathing
mode:
Amplitude calibration
Hydrophone modelling
Vc
Single order circuit model: 1R and 1C
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
Sheffield tank
• Limited by reflections in tank, shown here is response to
10kHz single cycle sine (measured and predicted)
B&K 8106 Hydrophone
(4.0 dB) 0.1 Hz to 80kHz
with B&K Amplifier
Amplitude calibration
Laboratory results so far:
Data Acquisition system NI
DAQ Card-6062E (for
PCMCIA) 500 kS/s, 12-Bit, 16
Analogue Input
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
University swimming pool
Excitation pulse
• Much larger dimensions so
not limited by reflections,
however large low freq
(~3kHz) background from
pool pumps (x2)
• Must dejitter pulses
because of large varience
in trigger level
Amplitude calibration
Laboratory results so far:
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
University swimming pool
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Time averaged
pulses after dejittering
give much cleaner
signal than in tank…
No filtering of
received signal here
There still remains
some features either
side of pulse,
currently testing 7th
order model to see if
an improvement can
be achived
Jonathan Perkin
Amplitude calibration
Laboratory results so far:
2007…
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
Kelk Lake
• Use of Kelk lake permits both tests over a large dimension
(>30m separation source-emitter) depth ~10m
Amplitude calibration
Laboratory results so far:
• Only mild background due to surface conditions, and the
occasional duck…
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
Kelk Lake
Amplitude calibration
Laboratory results so far:
• Hitting hydrophone hard (>10V peak input) appears to excite non-linear
modes - no longer guarantee increase in source level with corresponding
increase in excitation amplitude - requires compensation?
• Have satisfied ourselves we can see signal at 30m separation, and can
gain a factor of 10 in signal/noise with offline filtering
– Something like >90% of background is below ~2.5kHz - high pass filter
improves signal/noise
• Therefore should be able to see pulses from omnidirectional calibration
source on at least one of the Rona hydrophones when deployed in the
field…
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
Amplitude calibration
Linear phased array
• In analogy to the coherent emission of radiation along the
hadronic cascade resulting from a UHE interaction in the sea,
a linear array of hydrophones can be constructed to emit
signals in phase such that an interference pattern similar to
the neutrino induced acoustic pancake is formed
• Theoretical modelling thus far has indicated that between 6
and 8 elements are required in order to generate the desired
angular distribution of the acoustic emission….
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
• How many individual bipolar sources do we need to
generate a suitable pancake?
Amplitude calibration
Creating a bipolar pancake
• 1.2x1020eV pulse
simulated 1km
from source
• N sources deployed
over 10m with
(10/N)m spacing
• Study the angular
profile as a
function of the
number of sources
• Of order 6 to 10
hydrophones
(minimum) are
needed
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
• Refraction will deform our pancake….
Amplitude calibration
Understanding the environment
• Not so important at Rona (hydrophone locations
uncertain, thermaly well mixed water)
2007…
…Needs careful understanding of acceptance
of array geometry at deeper sites
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
Amplitude calibration
Proposed deployment in the field
• The ACoRNE collaboration has chartered a vessel
in order to facilitate the addition of calibration pulses
to the water surrounding the Rona hydrophone
range
• Awaiting confirmation from MoD(QinetiQ) of
readiness
• Will also deploy an SVP profiler
• It is imperative that a calibrated bipolar pulse is
successfully registered by the Rona array this
summer…
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
• Complete linear phased array device
• Deploy single + multi-element devices both at the Rona site
and any other available locations - Nemo test site?…
• The problem of deployment is an open issue, have not
resolved:
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Rigidity
Inclination, rotation
Amplitude control
Depth proofing
…
Amplitude calibration
Future amplitude calibration
activities
• However, if we get to the stage of worrying about this we
should be happy of our progress
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment
Amplitude calibration
Summary
• The ACoRNE collaboration has characterised the response
of a hydrophone such that a spherically emitted bipolar pulse
can be introduced above the Rona array
• Theoretical modelling has suggested that in principle 6-10
omnidirectional sources can reproduce desired angular
emission
• The single element calibrator will be deployed over Rona this
summer
• Future devices should be robust enough to deploy at >2km
depth
2007…
Jonathan Perkin
SUD Catania 07
Acoustic Cosmic Ray Neutrino Experiment