Parts were fabricated for the acoustic ground impedance meter and the instrument was tested. A rubber hose was used to connect the resonator neck to the chamber in order to suppress vibration from the volume velocity source which caused chatter. An analog to digital converter was successfully hardwired to the computer detection system. The cooling system for the resonant tube was modified to use liquid nitrogen cooling. This produced the required temperature for the tube, but the temperature gradients within each of the four tube sections reached unacceptable levels. Final measurements of the deexcitation of nitrogen by water vapor indicate that the responsible physical process is not the direct vibration-translation energy transfer, but is a vibration-vibration energy transfer

Becher, J.

Meredith, R. W.

English

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DEPARThENT OF PHYSICS
SCHOOL OF SCIENCES AND HEALTH PROFESSIONS
OLD DOMINION UNIVERSITY
`10RF01 K, VIRGINIA
technical Report PTR-81-4
PROPAGATION OF SOUND TRROUGH THE EARTH'S
ATMOSPHERE:
I. MEASUREMENT OF SOUND ABSORPTION IN THE
AIR AND
II. MEASUREMENT OF GROUND IMPEDANCE
12'1►^^^s^
By	 4	 OCT 1981
Roger. W. Meredith	 U-)	 RE CEIVED	 o
C NASA STI FACiury v
and
	
! ACCESS pEpr.
ti
Jacob Becher
Principal Investigator: Allan J. Zuckerwar
(from January 1 to September 28, 1980)
Final Report ( Revised)
For the period July [, 1980 - June 30, 1981
Prepared for the
National Aeronauti . s and Space Administration
Langley Research Foundation
Hampton, Virginia
O	 Under
Research Grant NAG1-15
Harlan K. Holmes, Technical Monitor
Instrument Research Division
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DEPARTMENT OF PHYSICS
SCHOOL OF SCIENCES AND HEALTH PROFESSIONS
OLD DOMINION UNIVERSITY
NORFOLK, VIRGINIA
Technical Report PTR-81-4
PROPAGATION OF SOUND THROUGH THE EARTH'S
ATHOStRERE:
I. %XASUREMENT OF SOUND ABSORPTION In THE
AIR AND
II. MEASUREMENT OF GROUND IMPEDANCE
By
Roger W. Meredith
and
Jacob Becher
Principal Investigator: Allan J. Zuckerwar
(from Janu4kry 1 to September 28, 1980)
Final Report (Revised)
For the pericd July 1, 1980 - June 30, 1981
Prepared for the
National Aeronautics and Space Administration
Langley Research Foundation
Hampton, Virginia 23665
Under
Research Grant MAGI-15
Harlan K. Holmes, Technical Monitor
Instrument Research Division
Submitted by the
Old Dominion University Research Foundation
P.O. Box 6369
wet 
	 Norfolk, Virginia 23508-0369
September 1981
PROPAGATION OF SOUND THROUGH THE EARTH'S ATMOSPHERE:
I. MEASUREMENT OF SOUND ABSORPTION IN AIR AND
II. MEASUREMENT OF GROUND IMPEDANCE
By
Roger W. Meredith' and Jacob Becher2
SUMMARY
This report summarizes work accomplished under NASA grant NAG1-15
since July 1, 1980. This work is described under four major subject head-
ings: (1) acoustic ground impedance meter, (2) automatic data-processing
system, (3) cooling system for the resonant tube, and (4) final results of
sound absorption in N 2-H20 gas mixtL:es at elevated temperatures.
ACOUSTIC GROUND IMPEDANCE METER
The fabrication of parts for the acoustic ground impedance meter has
been completed, and the instrument has been tested. The volume velocity
source, using the five-lobed cam and the LED-photodiode monitor, func-
tioned as expected. However, mechanical vibrations from the volume
velocity source produced chatter to such an extent as to overwhelm the
microphone signal. This problem was eliminated by unscrewing the resona-
tor neck from the chamber and reconnecting the two parts by means of a
rubber hose to suppress vibration. The neck is currently being modified
for mounting on the center post of a camera tripod. It can be lowered to
a favorable height above the chamber and connected with the rubber hose.
'Research Associate, Old Dominion University Research Foundation, P O. Box
6369, Norfolk, Virginia 23508-0369.
2Associate Professor, Department of Physics, Old Dominion University,
Norfolk, Virginia 23508.
AUTOMATIC DATA-PROCESSING SYSTEM
The Datel Inters:! analog-to-digital converter model ADC-HC12B ha:i
been successfully hardwired into the Apple II computer detection system.
A sample driver for handshaking the converter with the computer and con-
trolling the conversion rate is listed in Append.±x I. The program first
initializes the computer interface with the converter, then a 512, 8-bit,
byte base page is set up to store the 256 2-byte output from the
converter. Memory location 06 contains a code which controls the conver-
sion rate from 6 to 500 Hz. The 256 conversions are secientially stored
in the base page.
By controlling the sample rate, each free-decay curve representing
the sound absorption at that frequency can be stored as 256 digital data
points. The digital data can be stored directly on magnetic disk with the
following restrictions intrinsic to the computer's disk operating system.
Each free-decay frequency (256 digital data points) will be stored under a
separate file name and 105 file names are allowed per disk. Each set of
256 digital data Mints requires 1,024 disk bytes for storage where 252
digital points require only 768 disk bytes. This is due to the way in
which information is encoded on the disk. So `_.iare for graphing the digi-
tal data and evaluating the free-decay curves has been initiated.
COOLING SYSTEM FOR THE RESONANT TUBE
When the initial cooling system proved ineffective in cooling the
resonant tube to 0' C (32' F), the cooling system piping was insulated.
Even with the added insulation, the cooling system was ineffective. The
cooling system was modified to use liquid nitrogen coolant by passing
liquid nitrogen from a nearby trailer. The liquid proved to be sufficient
to cool the resonant tube to the required temperature; however, the tem-
perature gradient within each of the four tube sections reached unaccept-
able levels. Figure 1 shows the results of the cooling test and the
2
0	 25	 SO	 75
120
V0
SO
IS
s
TIME (HOURS)
3
Figure 1. Temperature gradient in one tube section. The large temperature
gradient results from liquid N^ going in one end and gaseous N_,
coming out the other end of the tube section.
3
resulting temperature gradient for one tube section. Modifications to the
cooling system are presently being designed and implemented so that each
tube section can be cooled more uniformly.
FINAL RESULTS OF SOUND ABSORPTION IN N 2-H20 GAS MIXTURES
AT ELEVATED TEMPERATURES
Final measurements of deexcitation of nitrogen by water vapor were
reported at the 100th Meeting of the Acoustical Society of America in the
fall o" 1980. The results indicate that the physical proce.s responsible
for thy : deexcitation is n..t the direct vibration-translation energy trans-
fer, but is a vibration-vib°ation energy transfer. The results also indi-
cate that ANSI Standard S1.2t"/ASA 23-1978 predicts an excessive shift of
the nitrogen relaxation frequency with humidity. This paper is reproduced
in Appendix II.
4
APPENDIX I
LISTING FOR CONTROLLING A/D CONVERTER
OP CODE	 MNEMONIC
A9 34 LDA #$34
8D Al CO STA $COA1
8D A3 CO STA $COA3
A9 25 LDA #$25
85 08 STA $08
A9 00 LDA #$00
85 FA STA $FA
A9 95 LDA #$95
85 FB STA $FB
A9 02 LDA #$02
85 09 STA $09
A2 3C LDX #$3C
AO FF LDY #$FF
A5 06 LDA $06
20 AS FC JSR $FCA8
A9 34 LDA #$34
8D Al CO STA $COAL
8A TXA
8D Al CO STA $COAL
C6 08 DEC $08
COMMENTS
initialize converter interface
code for conversion time
set up 512-byte base rage
index to base page
toggle to start conversion
DO FC BNE
AD AO CO LDA
91 FA STA
88 DEY
AD A2 CO LDA
29 OF AND
91 FA STA
CO 00 CPY
FO 03 BEQ
88 DEY
DO DA BNE
C6 FB DEC
C6 09 DEC
DO D2 BNE
60 RTS
$93E1	 wait until end of conversion
$COAO
($FA),Y
	
store low and high byte from
converter to base page
$COA2
#$OF
($FA),Y
#$00
$93F9
$93D3
$FB
$09
$93D1	 test for base page
6
APPENDIX II
SOUND ABSORPTION IN N2 -H2O GAS MIXTURES AT
ELEVATED TEMPERATURES
By
Allan J. Zuckerwar and Roger W. Meredith
Presented at the 100th Meeting of the Acoustical
Society of America, fall 1980.
7
^i
ff
r'
h
	 SOUND ABSORPTION IN N 2 -H20 GAS MIXTURES AT
ELEVATED TEMPERATURES
BY
Allan J. Zuckerwar and Roger W. Meredith
The purpose of our measurements is to make a decisive determination of
the physical process responsible for the deexcitation of nitrogen by water
vapor, and to compare the measured temperature dependence of the sound
absorption with that of the new ANSI standard, "America National Standard
Method for the Calculation of the Absorption of Soiind by the Atmosphere"
(S1.26/ASA 23-1978).
The first slide shows the results of sound absorption measurements in
a typical mixture of nitrogen and water vapor at three different temperatures.
The water vapor content for this particular composition is 3500 parts per
million. The sound absorption u, in nepers/wavelength, is plotted against
frequency/pressure (f/P) ratio. The data define a pronounced peak - the
vibrational relaxation peak of nitrogen - at each temperature. The value
of f/P at the crest of the peak is called the "relaxation f/P" or "(f/P)
max" and lies at about 60 Hz/atm for this mixture.
The data appear in a more or less uniform band about a baud curve,
owing to the random nature of the background damping. With increasing
temperature the accuracy of the measurement improves considerably as the
peak soars above the background. The solid lines represent the best fit
to the Debye relaxation curve, (f/P) max being the only adjustable para-
meter. The peak height was computed with the aid of the Planck-Einstein
formula. Eight such sets of data were taken at humidities ranging from
10 ppm to a maximum of 3 mole t•.
Slide 2. Here (f/P) max is plotted against humidity for 21 cf the 24
measured relaxation peaks. The data for the lowest value of humidity fall
beyond the range of the graph and are not shown. At low humidities all the
data lie on the same straight line, having a slope of 184 Hz/atm-mole %,
which is independent of temperature. This agrees well with Griffin's room-
temperature slope of 200 Hz/atm-mole %, reported at the CambridLe meeting
last year (ref. 1). At high humidities the data deviate from the linear
8
fit. At 298' K the deviation falls within the experiaental error. At the
higher temperatures the deviation lieu well beyond the error akd is con-
sidered a real physical effect.
Slide 3. On this slide the relationship between relaxation frequency,
referred to i atm, and humidity is compared with past results. At low
humidities our slope shows good agreement with that obtained by Evans (ref. 2).
The data of Chang, Shields, and Bass (CSB) (ref. 3), taken at much higher
humidities (starting at 4 mole %), yield the somewhat greater slope of 260
Hz/atm-mole 8. The problem is to reconcile the existence of two different
slopes at low and high humidities. Fortunately, theory enables us to do this.
Slide 4. The nitrogen-water vapor system is an example of a two-component
system, where both components are excitable. Deexcitation of the vibrational
degrees of freedom takes place by means of five reactions. The ruction rate
k10 for the d..excitation of nitrogen by itself is extremely slow and will
be neglected. The second reaction rate k 20 represents the ieexcitation
of nitrogen by water through direct vibrational-translctional transfer.
Trauitionally this reaction has been assumed to be dominant and leads to a
strictly linear relationship between (f/?) max and humidity, that is, to a
single slope. in the model that we propose here k23 is considered small,
and the deexcitation process takes place through the last three reactions.
Rate k30 represents vibrational-vibrational transfer between the nitrogen
and water molecules, k40 the deexcitation of water by itself, and kso
the deexcitation of water by nitrogen.
Slide S. The Tuesday-Boudart analysis yields the following sxpression
for the slope of the 2v(f /P) max vs. h relationship in terms of the
reaction rate constants. It should be noted that the matrix formulation by
Bauer for this particular system yields identical results, but the Tuesday-
Boudart analysis is chosen because it lands itself more readily to physical
interpretation. The reaction rates k 2 0 and k10 are neglected. Now
consider the remaining fraction. At low humidities only the leading terms
ii, the numerator and denominator are important, and these determine the
low-humidity slope S 1 . At high humidities the latter terms in the
numerator and denominator become dominant; and when only these are retained,
we obtain a different slope—the high-humidity slope S2 . Thus, the
theory leads to one value of slope at low humidities and another value of
L.
9
slope at high huuidities. The situation is quite different in the oxygen-
water vapor system, where the reaction k 03 is so large that the second
term ir, the denominator never really becomes dominant for values of humidity
normally encountered.
Slide 6. The ftr,ction Iro(h) is plott*d against humidity on a log-
arithmic scale. The circles are Griffin's data points at room temperature.
The triangles are the data of the CSB group (ref. 3). The solid line is
the best fit of the Tuesday-Boudart formula to both sets of data with k40
as the only adjustable parameter. Thus the V-V model not only accounts for
the existence of two slopes, but also fits both sets of data. There are
two possible objections to the V-V interpretation. First, the rate constant
k40 for the deexcitation of water by itself is smaller than the values
obtained from past experiments. The dash lines are similar plots using
other values of k 4 o derived from the literature. Actually, a value of
k40 as high As S x 107 is consistent with the data. Secondly, it mizht
be argued that a single straight line, with a slope somewhat less than 1.5
x 10 5 , would fall within the error bounds of the bulk of the data. This
is true for the room-temperature data and is our primary motivation for
obtaining the more accurate data at elevated temperatures.
Slide 7. Here we see slope versus log humidity for all three tempera-
tures. As before the solid lines are best fits of the Tuesday-Boudart
formula. At room temperature the existence of two slopes is barely notice-
able and concealed within the experiAental (rror. The situat-ion changes
at higher temperatures, where the change of slope at high humidity lies
well beyond the experimental error. A triangle represents a CSB point
at the closest corresponding temperature. Agreement is quite good.
Slide 8. This is a Landau-Taller plot for the V-V process. The
solid circles are derived from the low-humidity slope. The rate constant
represents a series combination of k 30 ar:d k S0 and is independent of
temperature. The remaining data belong to the high-humidity slope k30-
The solid line is the best fit to cur own and past data. The data chosen
to determine the line are those pants whose error bars intersect the line;
these include Henderson's point (ref. 4), three CSB points, Evan's point,
and three of our own. Each point is weighted according to how many
humidity values were used to establish the slope. The shock tube data
W^
10
L
of Huber and Kantrowitz (ref. S) show too such scatter and are not included.
Once we get above raoa temperature the error assigned to the various data
points demonstrates the existence of two slopes beyond any doubt.
Slide 9. We analyzed our own data and accounted for the 78 percent
dilution in air to compare our measured relaxation frequencies with those
specified by the new ANSI Standard. The values chosen correspond to the
extremes of temperature and humidity specified in the standard. The first
thing to notice is that the standard predicts far tft great a shift of the
nitrogen relaxation frequency with humidity. The standard is in error any-
where from 3S to 7S percent. Secondly, the standard does not account for
the cF=ge in slope. However, a tenfold increase in humidity produces only
a slightly greater than tenfold increase in relaxation frequency, so that
toe irror due to the two-slope effect is not very serious. Finally, a 40' C
increase in temperature increases the relaxation frequency by a factor of
8.5 according to the standard but by a factor of 13 according to measurement.
For frequencies below 2000 Hz, where sound absorption in nitrogen becomes
the dominant process in the Earth's atmosphere, the new ANSI Standard, while
more accurate than ar_ything available previously, could still lead to a
substantial measurement error.
REFERENCES
1. A.J. Zuckerwar and W.A. Griffin, J. Acoust. Soc. Am. 6S, S48 (A) (1979).
2. L.B. Evans, J. Acoust. Soc. Am. Sl, 409-411 (1972).
3. D. Chang, F.D. Shields, and H.E. Bass, J. Acoust. Soc. Am. 62, S77-S8
(1977).
4. M.C. Henderson st al., J. Acoust. Soc. Am. 45, 109-114 (1969).
S. P.W. Huber and A. Kantrowitz, J. Chem. Phys. 15, 275-281 (1947).
11
J
30 rst0^
	
MM ABSORPTION IN N2-H20 MIXTW ES
25
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♦ 20
v
p
s
Y • 3600 ^
P • 10 AT%
• •
••	 •
•	 •
3ss•K
•	 .	 .
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	 31s
FREQUENCY/ PRESSURE (Hz/otm)
Slide 1
12
1000
.. 100
E
0
NS
d
♦
10
VMTIONAL RELAXATION IN NITROGEN
tt/P)mgi VS. HUMIDITY
OL01
	
0.1	 1
	
10
HUMIDITY (mole %)
Slide 2
13
.1
a	 :	 s	 •
2
V
W'
a
W
Hs0 CONCENTRATION (MOLE %)
Slide 3
14
Reaction Rates
N= + NZ =NZ + NZ	(ki o , ka i )
Ni. + HZO =NZ + NO	 (k:o, kaZ)
N= + HZO WNZ + HZO* . (k3o, kas)
HZO* + HZO H10 + HZO (kao, ko4)
HZO* + Na HzO + NZ	(ksa, kas)
Slide 4
15
Slope According To Tuesday - Boudart
S(h) (Z*(g/p)max • kiol
ksekso + kso(k4o - kso)h
kss - kio + es + kso +
	
we - so - os
ksekse
3(h) ♦ S1 ' k20 - k10 +o^so	 (h sasll)
kto(k4o - kso)
t S s k - kl o+	 (h lame)S(h)	 z	 se	 k4a - kso - kos
Slide 5
16
Ls
.s
^ I.S
E
Ns
Z 0Av
_ 1n5
•3	 •2	 .1	 0
LOG HUMIDITY (male fraction)
Slide 6
L.
17
tE	 0
o Z
Z
c
w
N
•
cVN 0
W 2
_ ...s
SLOPE VS. HUMIDITY
O.. -	 n 	 .	 .	 l
.6	 -d	 -4	 •3	 -2	 .1	 0
106 KW QTY (moil traction)
Slide 7
18
a
s
7
s
S
..	 4
M
E
° 3V
2
too do0	 soo
a 10^
v
v
v'
V
v
v
v
v
TEMPERATURE (OK)
400
T
LAWU - TELLER PLOT
M2• ' 0 .= 
A2 « H2°'
O ZUCKERWAR i MEREDITH (HIGH H)
4 WERWAR i MEREDITH (LOW H)
e CHAM6. SHIELDS, 9 BASS
o EVANS
o HENMRSON ET. AL.
v HUBER i YWROWITZ
1
oil	 0.12	 013	 014	 Q15
(TERATURE)EMP	 (•K )L*1
Slide a
016
19
RELAXATION FRECIENCY OF NITROGEN IN AIR AT 1 AT1I
R.H. • lOZ R. H. - IOM
T•273°K Zan 8.65 Hz 87.18 Hz
ANSI 11.]1 111.05
T-31M zam 108.17 1154.44
ANSI 179.19 1791.90
Slide 9
20


Propagation of sound through the Earth's atmosphere. 1: Measurement of sound absorption in the air: 2: Measurement of ground impedance

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