Infrasound Technology Workshop – Tokyo, November 2007 1
Listen to the Soundsof the
Antarctic Atmosphere
L. Ceranna, A. Le Pichon & E. Blanc
BGR / B3.11, Hannover, Germany
CEA / DASE, Bruyères-le-Châtel, France
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Content
The Antarctic Infrasound Array I27DE
Observations and Signal Detections at I27DE
Conclusions
Future Work
• Design and Configuration• Noise Reduction and Performance
• Infrasound: Microbaroms and Mountain Associated Waves• Gravity Waves
• Neumayer III• Electric Power Generation using Wind Turbines• Reconfiguration of I27DE
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Location of infrasound station I27DE
5°W10 °W
71 °S
72 °S
Satellite Image of the Ekström Ice Shelf
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Site map of I27DE
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Array responses for two 9-element configurations
‘Pinwheel‘ Configuration
Concentric Configuration Array Response
Array Response
Co-Array
Co-Array
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Design and installation of hose arrays
16 arms: 90 and 70 m aperture
32 arms: 70 and 50 m aperture
16 arms: 70 and 50 m aperture
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The effect of wind
Comparison of different noise levels depending on wind speed
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Comparison of different noise levels depending on the rate ofsnow accumulation on top of the pipe arrays
Noise reduction by snow coverage
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Array performance as a function of wind speed
PMCC analysis in frequency range from 0.05 to 4 Hz, Jan-2003 – Dec-2005
mb-signals, [0.05 0.7] Hz
detection threshold
hf-signals, [0.7 4.0] Hzdetection threshold
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Detection of hf- and mb-signals, Mar-2003 – Sep-2007
~365,000 hf-detections, ~515,000-mb detections
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Average radial stratospheric wind speeds, HWM-93
motion of ocean swells along peri-Antarctic belt
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Amplitudes of mb-signals, Mar-2003 – Sep-2007
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Trace velocities of mb-signals, Mar-2003 – Sep-2007
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Amplitudes of mw-signals, Mar-2003 – Sep-2007
~41,000 mw-detections
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Trace velocities of mw-signals, Mar-2003 – Sep-2007
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Amplitudes of gw-signals, Mar-2003 – Sep-2007
~50,000 gw-detections
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Trace velocities of gw-signals, Mar-2003 – Sep-2007
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Example of gravity waves – bores at I27DE
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Comparison of detected signals, August/September 2004
wind
microbaroms
mountain associated waves
gravity waves
infrasound
• mb and maw signals are (completely) decoupled• infrasound signals and gravity waves are not correlated• trace velocity of gw signals indicates limits of infrasound detection capability
maw: VT{gw} < 10 m/s; mb: VT{gw} < 20 m/s• are measured wind and gw signals correlated?!
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Wave parameters of gravity waves and measured wind
β=82°±22°VT=17±7 m/sA=0.16 Pa β=238°±14°
VT=9±6 m/sA=0.09 Pa
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I27DE has demonstrated that its configuration and design are well suited for high wind conditions. It has been operated for more than 4.5 years without any major problems.
The average detection threshold of mb-signals can be estimated at wind speeds of 16 m/s, i.e., at almost 85 % of the time I27DE have the capability to detect infrasound signals showing typical mb-signal amplitudes.
Detection of mb-signals correlates well with a stable stratospheric duct obtained with HWM-93 showing easterly directions during the Antarctic summer (December & January) and westerly at other time of the year.
An anomaly in the number of detections and trace velocity was observed for mb-signals during the Antarctic winter, the reason for probable absence of the stratospheric duct is currently not clear.
mw-Signals are decoupled from mb detections in winter times, however regard during Antarctic summer mw detections are dominated by mb-signals. Moreover another source, being independent of stratospheric duct, exists in the direction of ~120°.
Conclusions I
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gw-signals are showing large amplitudes (gwE: 0.16 Pa, gwW: 0.09 Pa). These signals are NOT correlated to the stratospheric duct.
gw-signals are correlated to measured wind speed, both with respect to speed and direction.
Infrasound signals (mb + mw) are not correlated with gravity waves.
The trace velocity of gw-signals indicates limits of infrasound detection capability (mw: VT{gw} < 10 m/s; mb: VT{gw} < 20 m/s).
The data of all infrasound stations, especially those which are linked to the peri-Antarctic belt, should to be analyzed on a broad frequency range including gw-signals (50 – 500 s).
Conclusions II
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Neumayer III research base
L*W*H 68*25*28 m3
height above snow 6 m
weight 2400 t
floor space 1900 m2
‘life-span’ 25 a
Neumayer III
L*D 120*9 m2 [2x]
depth below snow -5 → 15 m
floor space 2000 m2
‘life-span’ 16 a
Neumayer
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Relocation of I27DE in 2008/09
• Neumayer III will be built ~5 km to south of the current Neumayer research base
• the construction work for the new research base will be started this year
• a close schedule has to be kept (note, vessels call at the station only twice a year)
• cables for power supply of I27DE will be laid out this Antarctic summer
• I27DE will be relocated 2008/2009 (if the PTS will hopefully realize that Neumayer is not just around the corner)
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Electric Power Supply at Neumayer III
• 3 * 30-kW horizontal axis wind turbines (< 100 dB aerodynamic noise)• 3 blades, 30 rpm, 15 m tower height, and 5 m blade radius, BPH=1.5 Hz
catabatic winds: ~180°, wind speed ~ 4 m/seasterly winds: ~90°, wind speed ~ 6 m/s
58 dB
54 dB