South Pole Acoustic Test Setup Calibration and lake tests. Freija

South Pole Acoustic Test Setup
Calibration and lake test.
Freija Descamps for the SPATS group*
*
S. Böser a, C. Bohm c, F. Descamps a# , J. Fischer a, A. Hallgren d,
R. Heller a, S. Hundertmark c, K. Krieger a, R. Nahnhauer a,
M. Pohl a, P. B. Price b, K. Sulanke a, J. Vandenbroucke b
a) Deutsches Elektronen Synchrotron; DESY, b) University of California, Berkeley;
c) University of Stockholm; d) University of Uppsala; #) on leave of absence of University of Gent
Outline
- The SPATS project
Goals
●Setup
●
- Sensor and transmitter calibration
Hydrophone calibration
●Sensor calibration
●
Setup
●Results
●
Transmitter calibration
●
- Frozen lake long range test
Goals
●Setup
●Results
●
Transmitter range
●Variations between transmitters
●Sensor directional information
●
- Summary
ARENA 2006
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SPATS: Calibration and lake test.
The SPATS project
Goals
Acoustic neutrino detection array ~> acoustic properties of the South pole ice ?
Deploy powerful acoustic
transmitters
and sensors
in first 400m of the ice sheet.
=> Absorption lengths
f/T dependant -> depth dependant
=>Horizontal spacing of strings
●
=> Speed of sound
Vice> Vwater => larger signals (P)
●Density dependant
=>refraction of surface noise
●
•Variation of critical parameters is
expected to be strongest.
•Lowest temperatures = optimal
for acoustic neutrino detection.
=> Background noise level
energy threshold
●
=>Transient events
Locate sources of background events
●
ARENA 2006
-2-
Use upper part of IceCube holes!
SPATS: Calibration and lake test.
The SPATS project
Setup: in-ice devices
In upper 400 meter
of IceCube holes:
-3 strings
-7 acoustic stages
Transmitter module
Transmitter
Sensor module
=>25 stages have been build and calibrated!
ARENA 2006
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SPATS: Calibration and lake test.
The SPATS project
Setup: transmitter
●
●
●
HV pulse generator
●
1kV@10µs
●
L/C circuit
●
Pulse read back system
Auxiliary T/P sensors
Ring shaped piezo ceramics
●
Generates broadband pulse
●
Azimuthal isotropic emission
●
●
ARENA 2006
better than cylinder shape
Cast in epoxy
-4-
⇒Shape and stability
of the pulse?
⇒T-dependence of the
pulse amplitude?
⇒Sound production
efficiency?
⇒Radiation behavior in far
field?
⇒Azimuthal and polar
variations in emission?
SPATS: Calibration and lake test.
The SPATS project
Setup: sensor
●
Steel housing
●
3 channels = 3 piezo ceramics
●
●
Mechanical contact
●
●
Individually calibrated (d33)
Preload screw =>Press the piezo’s against steel
Low noise 3-stage amplifier board
⇒Complex system with many different materials
⇒Different preloads?
⇒Resonances?
⇒Frequency dependence of the sensitivity?
⇒Equivalent self noise?
⇒Every complete sensor is different
Æ need to be calibrated individually
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Hydrophone calibration
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Setup
For sensor calibration, we need:
a) Sufficiently large water tank
->no interference with the direct signal
HSVA
“Hamburger Schiffbauversuchsanstalt”
-> 78mx10m (2 depths : 5m/2.5m)
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Setup
For calibration, we need:
a) Sufficiently large water tank
=>no interference with the direct signal
b) Broadband pulses
HSVA
“Hamburger Schiffbauversuchsanstalt”
HV pulses applied to
ring-shaped piezo ceramic
=>wide frequency range
c) Reference hydrophone of known
sensitivity
=>obtain pressure spectrum of the
broadband pulse
Has been calibrated to obtain sensitivity spectrum
=> signal spectrum [V]+ sensitivity spectrum [dB re V/mPa] => Pressure spectrum [mPa]
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Method
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Results
Hydrophone signal
SPATS-Sensor signal for one channel
Spectra for the signals [V]
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Results: errors?
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Results
Absolute Sensitivity [V/µPa]
Chan. 1
Chan. 2
Chan. 3
Pressure spectrum [µPa]
Spectrum for SPATSSensor Signal [V]
Sensor Module 3
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Results
Equivalent noise level [µPa]
Chan. 1
Chan. 2
Chan. 3
Sensitivity [V/µPa]
Self noise [V]
Sensor Module 3
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Results: overview for all sensors
I) Absolute sensitivity range for all sensors [dB re V/mPa]
hydrophone
Effective detection threshold
⇒Not determined by sensitivity
⇒Most important is signal to noise
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Sensor calibration
Results: overview for all sensors
II) Equivalent noise level [mPa] for each sensor module and all channels
hydrophone
Equivalent self noise level
⇒Different for each sensor
⇒For most modules < 30mPa
⇒Hydrophone: 150mPa
ARENA 2006
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SPATS: Calibration and lake test.
Sensor calibration and transmitter tests
Transmitter tests
Transmitter properties:
-> amplitude uncertainties due to directivity
azimuthal
polar
In final deployment
•no control of azimuthal orientation: ≈ 40% (for skew ring)
•possible tilting Æ polar orientation: < 10% for ± 10º
=> Directivity determines uncertainty in amplitude measurements
=> Overabundant system Æ will allow in-ice calibration
ARENA 2006
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SPATS: Calibration and lake test.
Frozen lake long range test
Goals
Test the transmitters:
=> What are the variations between different transmitters
=> What is the range?
Test the SPATS sensors, use commercial hydrophone as reference:
=> Can we determine direction of pulse using the 3 channels per sensor?
=> Is the SPATS sensor more performant than the hydrophone?
Test the DAQ-software
=> What is the rate of readout failures?
=> Can we readout all channels?
Test the hardware
=> How robust is the system?
ARENA 2006
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SPATS: Calibration and lake test.
Frozen lake long range test
Setup
Location:
=>Abisko, North Sweden:
• 68°21'N,18°49'E
• 385m altitude
• Lake Torneträsk
●
Large volume of water
=> reflections are expected to be clearly seperated from the signal
●
Frozen surface
=> easy deployment
=> relatively silent
ÆDeploy the transmitters, sensors and hydrophone:
ÆAt different distances (max. distance =800m)
ÆAt different depths (max. depth =64m)
ARENA 2006
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SPATS: Calibration and lake test.
Frozen lake long range test
Setup
Hole locations:
400m west
90 cm thick ice
TCH
400m south
400m west
5m
180m
100m
180m
400m
400m
800m
400m east
ÆDeployment:
ÆLower a complete stage
ÆIn-ice cable + support cable
ARENA 2006
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SPATS: Calibration and lake test.
Frozen lake long range test
Setup
TCH
400m south
400m north
AJB
ARENA 2006
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generator
SPATS: Calibration and lake test.
Frozen lake long range test
Results
Transmitter range:
Transmitter @ 100m distance, depth =-30m
Hydrophone @ -16m, gain =128
Sensor @ -16m, gain =1
scale!
Transmitter @ 800m distance, depth =-30m
⇒Signal/Noise
=1 @ 1800m!!
Sensor @ -16m, gain =1
ARENA 2006
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SPATS: Calibration and lake test.
Frozen lake long range test
Results
Variations between transmitters:
SPATS sensor @ 400m distance, depth =-30m
⇒10 events @ each depth
⇒’swinging effect’ Æ re-align first peaks
⇒take amplitudes of first peak
ARENA 2006
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⇒All transmitters are clearly heard @400m.
⇒Variations are within expectations.
SPATS: Calibration and lake test.
Frozen lake long range test
Results
Sensor directional information:
n
Sensor
STILL NEED
TO REPLACE THIS
PLOT
e
w
s
Insert graph showing
the direction here.
ARENA 2006
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⇒3 channels are each separated by
10.47cm steel.
⇒Expected delay for head-on pulse
= 2 x 10-5s (if v = 5790 m/s)
⇒Directional information can be
detained.
SPATS: Calibration and lake test.
Summary
=>SPATS calibration
-Sensors:
•75 channels have been calibrated in water
•Range of mean equivalent self-noise level: 11mPa-83mPa
-Transmitters:
•Azimuthal and polar variation of pulse emission has been quantified
•HV-generator is stable
•Acoustic pulses are reproducible
=>Outdoor long range test:
ÆA complete system test has been accomplished.
-SPATS sensors + transmitters meet the requirements.
-The system worked 'out of the box'.
ÆCalibration and verification has been performed
ÆThe Abisko lake test was a success
ÆSPATS is a robust system!
ARENA 2006
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SPATS: Calibration and lake test.
Backup Slides
In-Ice Calibration
ARENA 2006
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SPATS: Calibration and lake test.
Tornetrask attenuation length
ARENA 2006
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SPATS: Calibration and lake test.