Characterization and Suppression of Wind Noise Using a Large-Scale Infrasound Sensor Array Carrick...
-
Upload
isabella-pilch -
Category
Documents
-
view
213 -
download
1
Transcript of Characterization and Suppression of Wind Noise Using a Large-Scale Infrasound Sensor Array Carrick...
Characterization and Suppression of Wind Noise Using a Large-Scale
Infrasound Sensor Array
Carrick L. TalmadgeDoug ShieldsKenneth E. GilbertThe University of Mississippi, Oxford, MS USA
Infrasound Detection
sourcepropagation
receiver
• Source characterization (wave form, signal level, directionality, etc.);.
• Effects of vertical variation in wind-velocity and temperature profiles; including diurnal effects
• Effects of turbulent scattering
• Terrain effects
Must consider effects of:• wind-generated sound
• atmospheric turbulence (intrinsic pressure fluctuations)
• pressure probe body on pressure measurements
Robust system design needs data-driven models of all three components!
Advantages of Sensor Arrays
Arrays provide
•directionality (source location);
•noise reduction using more sophisticated DSP algorithms;
•the ability to separately characterize the signal and the noise.
Old Array Technology
NSensors
D
A/D
Signal Processing
Total Cable Required N2D/4
Example: N = 40 D = 5m L = 200m Total Cable = 2000m
New Array Technology
NSensors
D
A/D
P
A/D
P
A/D
P
A/D
P
A/D
P
A/D
P
Signal Processing
Total Cable Required ND
Example: N = 40 D = 5m L = 200m Total Cable = 200m
Smart Sensor Arrays
Components of smart sensor element:
• Ruggedized sensor and sensor body
• Signal conditioning with programmable gain and anti-alias filter
• Analog-to-digital stage with programmable sampling rate
• Microcontroller-based networking using RS-485 standard (~ 2Mbps data rate).
• Remotely controlled self-calibration and diagnostic testing of individual sensors.
Approximate delivery dates for bimorph sensors:
8 prototypes January 1, 2002
100 manufactured units March 1, 2002.
Second-Generation Array
RS-485 networked sensor elements
DSP-based“collector” units with RS-485 to wireless modem
wireless link
central processor
sub
arra
ys
Bimorph Capsules
• Resonant Frequency - 3 kHz
• Sensitivity - 1 to 4 mV/Pa• Temperature Compensation
– Reverse bimorphs– Insulated enclosures,
small openings• Charge Generating
– Must operate into a high impendence
Potted Capsules & Housing
Acoustic Sensor Development
Gabrielson Piezo-Resistive Transducer
Features: • 0.005 - 1000 Hz• High Sensitivity (20 mV/Pa)• Low Power Usage• Low Cost (Less than $250 per
unit)
9V Batteries
Add anti-alias filter and 24-bit sigma-delta A/D converter. Replace acrylic back volume with insulated
brass back volume instrumented for internal temperature.
Move first-stage amplifier onto sensor board (small-outline IC).
Oxford Airport Array Experiment
Chris Clark, Ken Gilbert, Doug Shields, Carrick Talmadge, Ron Wagstaff Chad Williams, Jay Williams, Zak Williams
Experiment took place on April 6, 2001
40 minutes of data were collected over an ~ 1 hr interval
2 microphone arrays, sonic anemometer
Levels calibrated using a B&K sound meter
(not to scale)
Experimental Setup
southB&K array (6x)
anemometer
bimorph array (11x)
Single Sensor (B&K) ResultsS
ensor #
Successive sensor outputs have been shifted by –10Pa.Run #1 (50-Hz tone) — initial 10 seconds of recording
Amplitude and Phase Shown is the amplitude and phase for the 50-Hz tone from the sensor 1 read-out.
The propeller-driven plane which lands around 150 seconds had no noticeable influence on the 50-Hz tone…
“pops”
“Prop” plane landing (CPA)
Run 1: 50-Hz tone
Run 1: 50-Hz tone
Frequency [Hz]
Pressure [Pa]
Time [sec]
Si g
nal
Am
pl i
tud
e
Frequency [Hz]
Run 1: 50-Hz ToneTime Series Spectrum (Fourier Transform)
RMS Averaged Spectrum
Time [sec]
Lev
e l [
dB
SP
L]
Cou
nt
Level [dB SPL]
40-Hz bin 40-Hz bin
50-Hz bin
60-Hz bin 60-Hz bin
50-Hz bin
Run 1: 50-Hz Tone median RMS
Run 1: 50-Hz tone Note that “pops” in playback create erroneous spectra using RMS spectrogram.
Median spectrogram is more robust and will be used here throughout.
Calibration of B&K sensors is excellent between 10-250 Hz (error is on the order of 1 dB).
(RMS)
median
Run 6: 25-50 Hz Tones, 5-Hz Steps
wind-generated sound
Yocona River Array Experiment
1
16
15
30
6.46 m
0.8 mile
Sound SourceObservation Station
Observation Station350 meters
Yocona River
Hwy 7
NPrevailing Wind
Sewage Disposal Plant
Prevailing Wind
0 500 1000 1500 2000 2500 3000 3500 4000-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
LAG TIME IN SEC X 500
CO
RR
EL
AT
ION
CO
EF
FIC
IEN
T
CORRELATION VS LAG TIME
correlation between sensors 1 and 3
wind(1) time = 5-45 sec
0 2 4 6 8
116
15
30
6.46 m
N
3
-3 -2 -1 0 1 2 30.4
0.5
0.6
0.7
0.8
0.9
1
CORRELATION DISTANCE (m)
CO
RR
EL
AT
ION
CO
EF
FIC
IEN
T
CORRELATION COEFFICIENT VS CORRELATION DISTANCE
WIND(1) SENSORS 7-12, TIME 5-45 SECNOTE LOW CORRELATION
-3 -2 -1 0 1 2 30.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
CORRELATION DISTANCE (m)C
OR
RE
LA
TIO
N C
OE
FF
ICIE
NT
CORRELATION COEFFICIENT VS CORRELATION DISTANCE
wind(1) sensors 21-26, time 5-45 secnote high value of correlation
Wind Noise Correlation Strength vs. Distance
Correlation Parallel to Wind Direction Correlation Transverse to Wind Direction
Separation [m] Separation [m]
Max
imum
Cor
rela
tion
Conclusions
• Large-scale microphone arrays are a versatile, transportable alternative to pipe arrays.
• In general, they provide superior wind-noise reduction due to the more sophisticated DSP algorithms which are possible.
• The three components of wind noise (intrinsic pressure fluctuations; wind-generated sound; probe-body induced pressure fluctuations) can be decoupled and separately characterized.