The infrasonic signatures generated by the main blade slap rate of a helicoper were used in an effort to detect infrasound generated by clear air turbulence. The artificially produced infrasound and the response of the data acquisition system used are analyzed. Flight procedures used by the pilot are described and the helicopter flight information is tabulated. Graphs show the relative frequency amplitudes obtained at various microphone locations

Badavi, F.

Becher, J.

Meredith, R. W.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19830006769 2020-03-21T05:03:42+00:00Z
O 
r,
r 	 DEPARTMENT OF PHYSICS
SCHOOL. OF, SCIENCES 'AND! HEALTH PROFESSIO-NS
OLD DCMf ION N UNIVERSITY
ORFOLKo , VIRGINIA
ft
TECHNICAL REPORT PTR- 82-17
LL
- PR'OPAGATI 'ON ' OF SOUND THROUGH THE"
EARTH' S ATMOSPHERE
ry
LU
;, Francis Badavi	 np
' Roger Meredith	 r-	 ^A
r	 ;^
3...
	
and	 c- NA 11
Jacob Becher, Principal Investigato +^^
W
Progress Report
4;,	 z	 For the period July 1 to December 1982
r
L Prepared for-the
O-National Aeronautics and Space Administration
„Langley Research Center
J„ Hampton, 'Virginia y
	))
G
_ Under	 t	 I
Research Grant NAG1--234
Harlan K. Holmes, Technical Monitor
0	 Technology Utilization aA', Applications Division
OiNASA- CR-169630) PROPAGATION CF SCUND	 N83-15040
i ZHROUGR THE BA TH' S PTMOSPEERE Progress
Report, 1 Jul. _- Dec. 1982 (Old Dcminion
Univ. , Norfolk, Va.) 23 p HC A02/Ml A0 1	 Unclas
CS.G L--- 2:0-A__G;3/7_i___
n
/f December 1982
rDEPARTMENT OF PHYSICS
SCHOOL OF SCIENCES AND HEALTH PROFESSIONS
OLD DOMINION UNIVFRSITY
NORFOLK, VIRGINIA
TECHNICAL REPORT PTR-82-17
PROPAGATION OF SOUND THROUGH THE
EARTH'S ATMOSPHERE
By
Francis Badavi
Roger Meredith
and
Jacob Becher, Principal Investigator
Progress Report
For the period July 1 to December 1982
Prepared for the
National Aeronautics and Space Administration
Langley Research Center
Hampton, Virginia 23665
Submitted by the
Old Dominion University Research Foundation
P.O. Box 6369
Norfolk, Virginia 23508-0369
December 1982
7
k^
Under
Research Grant NAG1-234
Harlan K. Holmes, Technical Monitor
Technology Utilization and Applications Division
.'
PROPAGATION OF SOUND THROUGH EARTH'S ATMOSPHERE
By	
5
Francis F. Badavi l and Jacob Becher2
SUMMARY
This report summarizes the work performed under research grant NAG1-
234, during the period of July 1 - December 30, 1982 in the specific area of
detection of infrasound generated by Clear Air Turbulence.
Detection of Infrasound Generated By
Clear Air Turbulence
Introduction
The purpose of the present work is to establish a possible correlation
between atmospheric turbulence and generation of low frequency infrasound
waves (frequency -0.1 -10 Hz).
Once the correlation of these infrasound waves has been established,
the detection of infrasound could be used as an effective method of
atmospheric turbulence detection and storm prediction.
The previous progress reports (research grant NAG1-142, July and
December 1981, and NAG1-234 June 1982), had described the technical and
instrumentational procedures and criteria employed for the present work.
The present report will be mainly concerned with the analysis of
artificially produced infrasound and the response of the data acquisition
system. These will be carried out under two headings:
1. System response to infransonic pure-tone; and
2. System response to helicopter noise.
'Graduate Research Assistant, Department of Physics, Old Dominion Univer-
sity, Norfolk, Virginia 23508.
2Associate Professor, Department of Physics, Old Dominion University,
Norfolk, Virginia 23508.	 k
fi
h^
u
t
ij	 tf
System Response to ;infrasonic Pure-Tone 	 p
n
To test the effect of local wind variations on the data -acquisition
system, a Bass-Reflex speaker was designed ^.:nd built to operate in the
infrasonic region (output 104 dB @ 1-m; Helmholtz Resonance frequency @
9.868 Hz). Figure 1 shows the location of the microphone array in relation
to the Landing Loads Facility (Bldg.-1262, LaRC).
Tn the actual field test, the speaker, with an accompanying electronics
and power amplifier (Crown-DC300 @ 300 Watts /channel), was placed in a van
and taken to three predetermined locations to study the wind effect.
The analysis of the recorded results showed that the microphones could
not be left exposed in the field and had to be placed in a protective con-
tainer, with a wind screen separating the ambient air from microphone
diaphragm. To lower the effect of wind shear on the container wall, a
coarse fiberglass cloth was employed to cover the top of the container with
two layers of soft foam providing seismic isolation. Finally the entire
assembly was buried such that the upper surface of the container was level
with the ground. Figure 2 shows the position of the container with respect
to ground level.. This method virtually eliminated the effect of wind shear
on the entire assembly.
Figure 3 is a typical noise response of the system before and after the
modification. The upper line is the system ' s noise response with exposed
microphone and the lower line is the response after the wind damping
container was employed. By the application of this method a considerable
amount of drop in response to wind was achieved, and the wind leakage into
the system was at an acceptable level.
System Response to Helicopter Noiie
The infrasonic signatures generated by the main blade slap rate of a
helicopter is a convenient source of artificially -produced infrasound.
To test the data-acquisition system sensitivity, a multi-location
hovering schedule was set on the afternoon of August 27, 1982. The specific
2
ORIC,jr4 '^L PAGE EV
OF POOR QUALrrf
N
(D MICROPHONE
LOCATION
100 FT
A0
^ o	 ^
INSTRUMENTATION
	 WYTHEVAN	
HOUSE
LANDING LOADS FACILITY
ARRESTING
GEAR
LUNAR
LANDER
A
Figure 1. Infrasonic microphone array.
Y	 x.14
3
ORIGINAL Q^AE M
OF PO QUALITY
C
C
0
C0L0
u
rd
a,
a,
b
G
3
N
4J
.r{W
CZ
C
v;Q
Or
LL
Z
'C.
ia
j
x.
1
tP
3 d
Ir	
^td:
N^k
f
4
yam,
s
ORIGINAL, PAGE rZ
OF POOR QUALITY
d
a,
v
u
b
o .^
0N
3
v
G0xa0
U
^O
4)
1J
C+
O
^N
C •rl
0
rr
0
.H
O
,G
C;
W
O
U
Gl
4-1
W
C+'1
o ^
N }^
0
bA
O
O
Z^
5
li
*'s
helicopter to be used was a Huey 204-B with a blade slap rate of about 10 	 t d
Hz.
The flight procedure was for the pilot to hover at a predetermined
location for approximately 60 seconds, during which time the infrasonic
signature was recorded by the operator. Upon completion of data taking,•the
pilot was instructed to increase his radial distance from the center of the
array. This procedure was repeated until a distance was reached where the
infrasound was rLot distinguishable from the background noise.
The purpose of this test was twofold. First, to determine at approxi-
mately what radial distance the system's sensitivity was, beyond an accept-
able margin, and second, to determine if the system hardware and analysis
method, developed for the work, was capable of finding helicopter's
direction.
The flight schedule called for the pilot to hover at ten different
locations, of which six were radial along a fixed bearing (approximately 3-
degrees west of north). The furtherest planned raidal location was approxi-
mately 25,000 ft (7500 m) away from the array's center. The other four
locations were circumferential at predetermined landmarks along a fixed
radius from the array's center.
Table I is a listing of the locationo and ranges from the array's
center and helicopter's altitude.
This data was later analyzed on a HP 5451-1, Fast Fourier Analyzer
computer for the purpose of time and frequency domain spectral analysis.
Figure 4(a-e) show the center microphone's response to different radial
distances. The upper diagram is the signal magnitude and the location of
fundamental frequency and it's harmonics in frequency domain, and the lower
diagram is an expanded display of signal in time-domain (total duration -
1.5 seconds). This diagram was expanded to generate a better time
resolution.
As can be seen from figure 4(a-e), the signal is strong at 2,400 ft
(720 m), 4,000 ft (1200 m) ! 8,800 ft (2540 m), and 13,000 ft (3900 m), but
Y^
6
C'
ORIGINAL
.r^' F,.
OF POOR QUALITY
a z
TABLE I. HELICOPTER FLIGHT INFORMATION$
h
STATION #	 LOCATION	 RADIAL	 ALTITUDE
DISTANCE	 (METER) FEET
0	 POQUOSON TRAILER	 (720) 2400	 (BO) 500
TRA I LERPARK
1	 HOUSING	 (1000) 4000	 (210) 700
DEVELOPMENT
2	 HUDGINS ROAD	 (2640) 8800	 (210) 700
3	 RIVER ROAD	 (3900) 13000	 (210) 700
4	 ROBERTS CREEK ENT.	 (5400) 18000	 QIO) 700
S (CANCELED)	 YORK POINT	 (7500) 25000	 r
A	 BACK RIVER	 (1200) 4000	 (180) 600
B	 CHAPEL ROAD	 (1200) 4000	 (180) 600
C	 LRC , BLDG 1212	 (1200).40M	 (180) 600
X	 TEST LOCATION	 (1<'.00) 4000	 (180) 600
.	 r
a
M5
N	
`Y
IFS:
}	 rye+
ii	 ^^
ORIGINAL V-4q r : J
OF POOR QUALI'' V
a
x
^F
8
I	 u
OON
Oa
3Qa=aw 3lLLLVI 3
O
O
4'
U
O
V	 A
E	 G
O
4a
O
9	 N
u
cdv
Gl
O
b0
•H
44
•t
0
8
f
r
~ -N e 
81 
~ i ; 
0 
CD 
Q 
.. 
OR\G\Nfl.\. pf.\Gi,. J 
Of pOOR QUA\..\it' 
~ 
! 
e 
en 
· Q 
ID 
· Q 
M 
· Q 
Q 
. 
~ 
'*" r:: 
;l 
~ 
~ 
0 
-
,...; 
1 '" 0 '*" 
-
Cll 
r:: 
.! 0 ,.c:: P-o ,.. 
tJ 
oM 
~ 
. 
,-.. 
,.c 
'-' 
..::t 
Cll 
~ 
btl 
'r-! p:.. 
9 
PAW"'
Of Poor."I of-!r,"
0
0
N
O
O
A
0
If!
F-4
C4
4
C4
.0
ri
td
0
r
C;
R
0
60
.H
rT4
10
OF
 P
POOR QUALITY
_,	 .-
0
M
OO
^ tS1
V
O
e—I
r. w
O
p"
E-4
u
o
b
v
O
F+
O
00
•;3 a
W
O
i{
z
-+i
z
{
l
8N
O
tD
N
v
N
w
H
T
Oq.
W
QRIGINP+L P ^,
aF pooR QUX%'
O
O
12
3u]LI^IcLt^I'K
•
N
rl^
O
*r•i
. .1.7O ^
U
O
n
b w
O
O
v
^ Q
v O
1 .0a
O
E-4 u
Ol
v
NT
41
H
00
W
4at WON ft (1400 WO 00, Opowte"m broko t1owtv a ►l obseuro poAkil 
At 
11 t 16,5
Ail ►
 17 On v01.'O obkiorvikl, IM114 abliormality 
Is 
thowil ti, ftgueo 4(0-),.
i
boo to Olt# drop LA sig"41 to Alotao ratio 
-it was do%l ,Wod thAt" t4tAttou
At 25 V 000 ft (7500 110 ) Should not b^ tr:(OC
At prohoilt A %'logv all"Wov 
to 
*p0,Qtrkl11% broAkl)wil, At U t 000 ft (SA-00
hakk 11ot b0ou e-k►lly doQW00 "
 11"wovot ! It 1'4 jlo4s3.1r1.ot that #oll►^ uoulivioar
Sri emitribmtllig 
to 
thbi bro#kdowil,
Nk^,A%is# or waimpul g ivq bolulvior of lis, umal ly-1wodkw, Ott filfegliouW
higiiAturo, It wAiA dowidod Mist Owl ttlIM k101114111
14 Alot A mvttablo Avovuxo to follow., (hi. tho o0vorbAml ) A gouo^rll purpoto',
Not lk)kivlov eoutillo ippo#rod tit
	 A moro ftoxtblo Approd0l"
Usod oil 00	 "Abovo, 1M)88-I)OW-01' #1)00,trU1%k INA10114,111011 *Ad
botwoom Ow	 Awl mL!voj11%%mlO A, Tho- pxxrpow~ of
tbittl WA14 r0l ObtAivil a	 1i111gilit"110 spOWWPAIM MAI fl%14 00. OXjkrt VA!"O
of A NO"milo-lital rroquouO," I)OW0011, tvh) MWrOIA10110-0, TWA OXdV3 L' VAIMO- Ot tlM
Nwidamolltal froquomn' t vllado^ It pogotblo to obtAlil All ompautiod
pboo 81*a -mim W11101 gavtA tho pha*0 lut-Ormatioll botwowit two 111volAug
digmlo,
thO	 Thig 1),Art of tho- vork wild tarrlc^d out by
kkAIIIA all AlAOIA01111 dON0,1000A oil A popular brand \WtAk-top
h0t1O.Oft \!MAOI.` %U'vollbouO^ Avid mUroplvollo-
At A"d 1110 4.OfttOV	 10 A	 t^\XJMWIOA OWOM^-JWWI:4 141490, dtd^vakll
armuld t110 
bill 
thAt 1^41.ttOd OVO,
	 VT)VVFA9j)0hkffi19 0 fuudd-
11%0041 rr6qkwm 'yr Altio IwAxldfAd to tlwk	 ot tll^ tuildmitutal
fvqquolviy at bottom witl% Olift
	 At LAW V-1 011tot t)f tho- Abgeidm
AkA Q411 4 good from r1gurol 5(A-0?, th@ imm g-pow'-hr %apkitud'o deoppod
vory 1'4p1dly \Atii, imromlillg radial dig talwo t	 Av%kl At 1,4 1 000 ft (5400 %) only
4bo rulldmio%itAl AM 010 obmQxvr@- 11, 16 AkAd 17 Ilia
This problo-vik 	 ivi 0 ,10 e"AI'mildtImi, of
Mdi"A duo to 01,dittvl%, W041t AW	 ixotso,
ORIGINAL PAGr: IS
•
	 OF POOR QUALITY	
D
O	 ^	 ^
i
Z=VIJJMI
O	 e^	 O
1
\^ s
I
O	 p
v ^ •0
a
V1 ON
40
	
I^	 v
O	
•N	
N
o ^
N
tor.
	
DM • ciylEt • O '^	 — ^n^Z^r
^	 Q
I
m
O
O
0
z	
O
O	
Sri
J-1
Cd0
U
'O	 r 
8	 o
M	 O	 O
v
Q
O
a
O
s'a
v
m r:
o v
o u)i
v
GO
rl
%C
O
1
14
ORIGINAL PAGE IS
OF POOR QUALITY
co
o	 `i	 Wo
N
to
00
v	 co
m	 1
O
•O
O	 ^
10	
mr
V
	
	
V
Q
a
N
.Ch	 N
o
i
'O
d'	 O
"lam	 O	 ^3Q
1
O
O,O
•r
0U
O
^ d
Q
8	
O V
	 ^,
Q
,a
0
s•+
U
I	 ^
.0
u't
O 41
1
rl
FT+
s A
15
m	 N
0
O
iJ
UO
r-1
a
cn
9
37f1 17dp& 3AIxv-,
 i
O
1
t	 ^
4 ^
yU
	 O
O iT1	
to
°	 0
O4
a
O
sa
u
Uu
co
O
I	 ^
b0
W
li
st
O
ORIGINAL PAGE
0 POOR QUALITY
^ N
n ^ .I
O
^	 J
O
0O
O	 1
CID	 O
r-1
'n
'	 N1
1D
N	 S
v
	
S	 N	 'V ^^ I
ul
En	 a9	 cn9
N
N	
u	
,O{
•O
Q
P
•
O
^t11LI'Z^l1t 3AI.I.F^L^i ° ^ t0  ' Jam' ^^t1 . ^
it
f]
d
r
j	 'd
16
4C'
FP
^ W
ORIGIAL PAGE 19
OF PO QUALITY
-4
Ln
O	 cc	
P-4
co
O
0
.rj
o	 -W
ti
CD
00
0
p
oho
Ln
cc
0
N	 C4
N
33riLirlaw Z% IXVM
*03a"M
^D
O
l
Lnv
•
L
U,	 O
	
e O	 ^D33-&M. e ^ rl
	
tD	 I
3j1 rl&i'd S&Lrf=
4^.
r
r
ORIGINAL PAGE 19'
OF POOR QUALITY
•o
a
o m
m
in
cc
cn
0
a
,e
o	 `o
°'	 o
^o
N
N	 --	 8
^^y	
o
V
^L	 •
O	 ^	 C O'
m a
0
0
u0
I0u
CD wo
a0
as
u
n
N
tr ;
mO ^
O ^I ^
.r{
W
a
18 ^t
+t
lip
Table II(a) is the result of the direction finding algorithm for the
radial part of the flight. it is obvious that increasing radial distance
t.
beyond 18,000 ft (5400 m) induced difficulty in finding a "sharp" direction
for the source.
`•
	
	
Table TI(b) is the same kind of tabular result,' for the circumferential
part of the test. Location x was picked randomly by the pilot, as requested
by the system operator, to test out the software capability in finding the
proper direction.
Conclusions
The research work at the start of this project was broken down into the
following catagories:
1. Analog Instrumentation;
2. Digital Instrumentation: Direction finding Algorithm;
3. Test with known Infrasound: Helicopter and Speaker;
4. identification of Natural source of Infrasound;
5. Corroboration: Aircraft, Doppler Radar;
6. Second Station (Wallops Island) for triangulation.
At present the first three parts of the project are almost completed,
and our accomplishments for the duration of thi p
 progress-report have been: 	 ".
i
1. Algorithm for signal processing; 	
r,
2. Novel windscreen; Reducing background noise;
3. Successful test with calibrated infrasound source;	 k
4. Successful test in finding the direction of hovering helicopter.
19
0—C
—10
O
_g
_7 °
0
_3
0
—4
-	 Iti
ORIGINAL PAGE 19
OF POOR QUALITY
TABLE—II(A). HELICOPTER AZIMUTH REFERRED TO O—A. AXIS.
MEASURED  AZIMUTH
O—A 0—B
—4 0
—60
—6 0 _8
—8 -10
o
—28 . —13
RANGE (FT)
2400
f	 4000
8800
1300r'
18000
E)
SCALE: OA = 100 FT(33 METER)
O
A
O
0
O	 O
B	 C
20
RANGE MONETER) 4000 FEET	 ¢-g
STA — A	 90"
e
STA — B	 314
STA — C	 190
STA — X
	 241.
I
ORIGINAL PAGE ES	 ` r
OF POOR QUALITY
TABLE II (B). HELICOTER AZIMTH REFERRED TO OA AXIS.
MEASURED AZIMUTH
o
83 96'
306 315
165 175 
6
241 239
SCAM; OA = 1D0 F r(33 METER)
0
A
0
00	 0
B	 c
21


Propagation of sound through the Earth's atmosphere

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server