APROPOSED SYSTEM
FOR AVIATION
NOISE MEASUREMENT
AND CONTROL
FTL COPY, DON'T REMOVI'
33.412, MIT a. 02139
Robert W.Simpson
Anthony PHays
R73-2
January 1973
A PROPOSED SYSTEM FOR
AVIATION NOISE MEASUREMENT AND CONTROL
R.
W.
A.
Simpson
P. Hays
R73-2
FTL REPORT
January 1973
A PROPOSED SYSTEM FOR
AVIATION NOISE MEASUREMENT AND CONTROL
FTL Report R 73-2
January 1973
Abstract
This report reviews previous work on various measures for
aviation noise, and proposes a completely new system for aviation noise measurement and control compatible with real time,
operational noise monitoring hardware. This new system allows
new methods of control and regulation to be introduced and is
designed to cover problems arising from future CTOL, RTOL, STOL,
and VTOL aviation systems operating from current airports as
well as new urban sites. New measures are proposed for aircraft
flyover noise, airport noise exposure, and community noise impact.
TABLE OF CONTENTS
Page
Title
Table of Contents
Definition of Terms; Nomenclature
1.0
i
ii
Introduction
1.1 Purpose of Report
2.0
1.2 Noise Control Options
2
1.3 Classification of Aviation Noise Measures
4
1.4 Outline of Report
7
Measurement and Control of Aircraft Flyover Noise Level
8
2.1 Measurement of Time Invariant Noise Levels
8
2.2 Proposed Method of Measuring Time Invariant
Noise Levels
15
2.3 Duration Correction for Flyover Noise Level
17
2.4 Proposed Method of Measuring Flyover Noise Level
22
2.5 Regulations for Controlling Flyover Noise
24
2.6 Proposed Regulations for Controlling Flyover Noise
33
Measurement and Control of Airport Noise Exposure Level
37
3.1 Measurement of Multiple Event Noise Level
37
3.2 Proposed Method of Measuring Airport Noise Exposure
Level
43
3.3 Regulations for Controlling Airport Noise Levels
45
3.4 Proposed Regulations for Controlling Airport Noise
Levels
47
Measurement of Total Community Noise Impact
49
4.1 Measurement of Community Noise Impact
49
4.2 Proposed Method of Measuring Community Noise Impact
54
5.0
Summary Review of Proposed System of Aviation Noise
Measurements
58
6.0
References and Selected Bibliography
61
3.0
4.0
DEFINITION OF TERMS; NOMENCLATURE
The following definitions are given here in order to have
some precision in using the following words:
SOUND:
pressure waves in the atmosphere which produce a response in the human ear.
NOISE:
sounds that are subjectively displeasing to the listener
under a given set of circumstances .
NOISE LEVEL:
sounds are weighed by frequency to
account for the response of the human ear, and compared
on a decibel scale to a reference sound.
The particular
type of weighting used should always be stated.
ANNOYANCE:
subjective reaction to noise.
The method of
quantification has not been universally accepted but a
doubling of annoyance for every lOdB increase in noise
level is frequently used.
NOISE EXPOSURE:
the effect of several noises heard at a
single point over a period of time.
NOISE IMPACT: measures the total effect of noise exposure on a
community and should consider such factors as local
background noise and population density.
ii
NOMENCLATURE:
an attempt has been made to follow modern practice
where x is the
x
(e.g., Perceived Noise Level is
and write all decibel levels in the form L
the type of measurement
written L PN).
Where additional clarification is required
Noise Pollution Level
A
Several
using A-weighted sound level may be written L N.
NP
noise measures (such as Composite Noise Rating, Noise
a superscript may be used, e.g.,
Exposure Forecast, and Noise and Number Index) should,
strictly speaking, be expressed in this form also, since
they are also decibel levels.
However, their nomenclature
is most commonly expressed as CNR, NEF, and NNI, and
this is
followed in
this report.
iii
1.0 INTRODUCTION
1.1 Purpose of Report
The initial goal of this research was to suggest new
measures for controlling the noise from future VTOL and STOL
aircraft.
In view of substantial differences in the time
histories of flyover noise for takeoffs and landings, in view
of proposals for future operations into built up city center
areas
and in view of forecast noise levels for rotary wing
vehicles which are close to urban background noise levels, it
was felt that the existing CTOL measures
for
V/STOL aircraft.
were not equitable
During the course of this work,
however,
it became apparent that there was a lack of coherence in the
present
methods for
measuring aircraft and airport noise as
they had developed over the past decade.
Thus, rather than
proposing a new and different methodology for VTOL and STOL
aircraft, it was decided to propose a complete new system
for measuring aviation noise.
This unified structure would be appropriate to current
and future problems in noise control, and consistent for
CTOL, STOL, and VTOL aircraft operations.
It was decided that
the structure had to be compatible with the implementation of
real time, airport noise monitoring systems now being introduced
at major airports around the world.
This meant
abandoning
the "perceived noise" concept, but it was felt that these concepts had clearly been shown to be unnecessary anayway.
A
return to simpler measurement scales provided substantial benefits
in terms of operational and regulatory flexibility.
The purpose of this report then became to propose a new
global structure for measuring the noise from aircraft and airports appropriate for the present and future problems of noise
control in aviation.
1.2 Noise Control Options
All systems for measuring noise are developed with an
ultimate purpose of controlling the noise in some manner.
The
system of this report allows a wide variety of noise control
options to be available.
However, it is not the purpose of
this report to advocate the use of any of these options, or
to establish allowable noise levels within an option, or
suggest any particular noise control agency.
These
to
are questions
to be resolved by political processes.
The options in noise control are briefly outlined by
identifying the following elements.
1.2.1 Noise Control Agency
The agencies responsible for carrying out noise control
may be classified as operator, local, and federal.
The airport
operator as landlord has the right to impose conditions upon
users of his facility to protect himself from lawsuit
In the
U.S.A., local government agencies may impose conditions on noise
levels from activities occurring in their area, in the absence
of pre-emption by federal agencies acting in the name of interstate commerce or environmental protection.
At present, all
three of these agencies may be trying to control the noise at
an airport
(e.g. Los Angeles).
While political and legal
processes will eventually determine the relationship between
these agencies for controlling noise, it is desirable that they
all adopt and use a common system for noise measurement.
1.2.2 Methods of Controlling Noise
The controls used by these agencies may be classified
into the following three methods.
1.2.2.1 Control of Noise Generation
This method suppresses the noise generated at the source
by requiring the manufacturer to meet standards for new aircraft, or supply retrofit items to quiet aircraft produced earlier
-2-
WIN No"$
11#1ORM
1.2.2.2 Control of Noise Exposure
This method controls the number and kind of aircraft
activities at a given airport.
It produces quotas and
curfews on the number of operations over some period of time,
and specifies operational procedures and flight paths to
minimize the exposure of the listeners to the noise source.
1.2.2.3 Control of Noise Impact
This method controls the noise received by listeners
by zoning the land around the airport to prevent an influx of
listeners, by acquiring land and removing listeners, by
soundproofing buildings, or by supplying compensation for
noise.
1.2.3 Noise Sanctions
Noise control methods have two main options in their
execution.
They may act by fiat, either by specifying a limit which
must never be exceeded, or
ee results in
by specifying a limit which if exceed-
economic penalties.
This is the only option
exercised to date, and it only controls the upper bound or
extreme which noise levels may reach.
However, another major option in executing noise control
is to apply economic sanctions on all noise generated above
a given level of quietness.
This "dollar per decibel" approach
applies pressures on all noise generated, and controls the
average level
of noise, rather than the extreme values.
-3-
1.3 Classification Scheme for Aviation Noise Measures
We shall classify noise measures used in aviation into three
distinct categories:
1) those used to measure noise from the single flyover of
an aircraft.
2) those used to measure noise exposure over time from a set
of aircraft activities at a point adjacent to an airport.
3) those used to measure noise impact over time and over the
area of the communities around the airport.
The proposed measures are based upon this classification
scheme.
The reader should especially note that the words
"exposure" and "impact" are used in a very precise manner.
We
shall now discuss current measures in terms of their classification.
1.3.1 Aircraft Flyover Noise Level Measures
Existing measures such as LEPN, or LSENE
(California) are
designed to measure the maximum intensity level of the noise
made by a single aircraft overflight.
They are measures of the
noise generated by a noise source, where that source is the aircraft.
Effective Perceived Noise Level, LEPN,
part of U.S.
is currently used as
regulations which specify noise limits for jet
transport aircraft
as part of the certification
craft for public use.
subsonic
of those air-
The limits apply to precisely specified
flight trajectories, under standard weather conditions, and with
the aircraft at certificated full operating gross weights.
The
method of measurement requires detailed computations based on
field measurements,
until
and the results are usually not available
days after the tests.
- 4 -
The noise levels under these specific conditions are only
rarely duplicated in actual service.
Due to lesser gross
weights, wind and atmospheric conditions, and non-standard speeds
and flight trajectories, the operational noise levels vary quite
widely from the standard cases.
If it is desired to impose a limit on operational noise
levels, or if a noise tax
(dollar per decibel) scheme is to be
instituted, it becomes necessary to use a measurement of aircraft
flyover noise level which can be recorded in real time.
The cre-
ation of this measurement and its control schemes argues for
changing the present certification measurement to conform closer to
operational procedures.
1.3.2 Airport Noise Exposure Measures
Proposed measures such as CNR, NEF, and existing measures
such as NNI and LCNE (California) record the noise exposure over
some period of time from multiple aircraft operations at a single
point in the community surrounding the airport.
Here we shall
use the term "exposure" for such measures and restrict the
general usage of that term.
The locus of points of equal ex-
posure is a "noise exposure level contour" which may be mapped
around a system of runways given the operational history over
some period of time.
Due to the differences between operational and certificated
noise levels, it is important that the actual operational noise
exposure levels be measured by "airport noise monitoring systems".
This willrequire real time field measurements to produce hourly
levels of noise exposure.
Future raeasures adopted should be con-
sistent with the real time measurement of flyover noise.
The community noise monitors may be used to control the frequency or type of operations at a given airport to keep noise
exposure below hourly, daily, or annual limits.
If a compensation
scheme is instituted, payments or property tax credits would be
based on the actual exposure
recorded in the community.
-5-
1.3.3
Community Noise Impact Measures
Where as noise exposure meas~ires cumulated noises over
some time period, noise impact measures are defined to accumulate
over both time and area.
In this class are proposed measures such as "footprint area" for
some NEF contour, ASDS footprints measured in "acre-minutes",
TCAM (Total Community Annoyance Measure, see sec. 4.1.2), and W
(Community Sensitivity Weighting, see section 4.1.3).
These "impact" measures are not as widely developed as
the
measures in the previous two categories, but are vitally
necessary in various planning activities.
They would be used to
plan preferential runway operations on a daily basis, to assist
in siting new runways or airports, to measure the benefits from
new aircraft operating procedures, or to measure the benefits
from changes to existing aircraft such as engine or nacelle
retrofit.
Notice that none of the measures of the previous two
categories are useful in answering these planning issues.
It is
desirable that future measures of impact be consistent with the
measures used for aircraft flyover and airport exposure noise.
- 6 -
1.111-
- --- mm
..
VMWOO"
__ -
- -
___
10.."..
___11
---
,
1.4
Outline of Report
The report is structured into three major parts correspond-
ing to Aircraft Flyover Noise,
Community Noise Impact.
Airport Noise Exposure,
and
In each part, measures of noise developed
in tha past are described, and a new measure is then proposed .
In the parts on Aircraft and Airport Noise, present noise control
regulations are described, and new methods of regulation are
proposed.
A summary review of the proposed System of Aviation Noise
Measurements is given at the end of the report.
-
7 -
2.0
MEASUREMENT AND CONTROL OF AIRCRAFT FLYOVER NOISE LEVEL
2.1
Measurement of Time Invariant Noise Levels
Objective noise measures, such as Overall Sound Pressure
Level, are of little use when trying to measure the loudness
of a sound.
The ear is most sensitive to sounds in the fre-
quency range of speech
(1,000 -
5,000 Hz) so that two sounds
with the same overall sound pressure level but different
distributions of intensity across the frequency spectrum may
appear to be of different loudness.
Single event noise measures
may be divided into two classes:
1) measures that relate to an instantaneous or time
invariant level of sound,
2) measures that relate to the duration, or time
variation
of the sound.
In the former category are A-weighted sound level and Perceived
Noise Level and in the latter category are Effective Perceived
Noise Level, and Single Event
Noise Equivalent Level
(California
Noise Regulations).
Definitions of other noise levels that are not directly
applicable to aircraft noise, such as Loudness Level, Articulation
Index and Speech Interference Level, may be found in Reference 1.
2.1.1 A-Weighted Sound Level
The earliest measure formulated is the A-weighted sound
level
(LA).
It is important because it is easy to use, has
been universally accepted as a standard, and relates reasonably
well to judged assessment of the annoyance of noise.
Sounds
are frequency weighted, and the weighting is based on the
apparent loudness of a sound relative to a tone of 1000 Hz.
The distribution of the weighting is shown in Figure 2.1;
the Sound Pressure Level at any frequency is multiplied by
-8-
+10
~
~~
PERCEIVED NoIsE
40c NoY
0
4
~
1
CoN-TouR
j
-10-
-20
Li
-
-30 -
-40
2 -50-
e0-6
--70
.0
1, 000
100
Freque'ncy, cycles per second (or Hertz)
F igure 2 .1- A COMPA RISON OF A-WE IGHT ING AND PE RCE IVED NO ISE
WEIGHTING
-9-
(from Ref. 2)
10, 000
the weighting corresponding to that frequency, and the overall
sound level is found in a manner analogous to finding the
This weighting may be done by
Overall Sound Pressure Level.
a simple electrical weighting network, so that the sound level
may be displayed directly on a meter.
2.1.2 D-Weighted Sound Level
The D-weighted Sound Level
(also called N-weighted
Sound Level) is similar to A-weighted Sound Level, that is,
frequency weighting and summation on an "energy" basis.
The
only difference is in the shape of the frequency weighting
curve, which for D-weighting corresponds to the "40-noy" contour
(see Figure 2.1) which is used in the calculation of LPN.
D-
weighted Sound Level appears to correlate slightly better than
A-weighted Sound Level with judged noisiness, but because of
its later introduction it has not gained as wide a recognition
as LA'
2.1.3
Perceived Noise Level
When jet transports came into service it was thought that
the A-weighting network underestimated the annoyance of jet
noise as compared with propeller driven aircraft.
A new
weighting formulation was developed based on'hoisiness" and
"unacceptability" rather than "loudness"
as Perceived Noise Level
(designated L PN).
-
this measure is known
Two important
differences between A-weighted sound level and Perceived Noise
Level are:
2.1).
1)different weighting is given to sound
(see Figure
The weighting at a given frequency also depends on the
Sound Pressure Level at that
frequency.
2) The calculation
takes account of the "masking" effect of the most prominent
part of the noise spectrum;
that is the noisiness in "noys"
of 1/3 octave bank levels, apart from the loudest, are reduced.
-10-
L,
One-Third Octuve £'ind Center Frequencies f, HZ
dB
63
50
100
s0
125
160
200
250
315
500
4A
800
630
1000
1250
1WO
2000
2500
29
30
)1
3
33
N O Ys As a Function of
Sound Pressure Level.
Table 2 .1
34
-00
1.07
1.15
31.2
-fro
(f rom
Re8f
1.00
2
,.07
0
41
42
45
1.70
-
44
1.00
1.08
40
50
5n
1.00
1-09
1-11
5
129
54
60
61
62
63
64
6
6'
64
69
V
11
72
)
74
17
7,
'9
0
1
0)
M4
il
1-17
2.00
2.t4
2.30
2.44
2.64
2.00
2.14
2.3:
2.4
2.64
2.93
2.13
03
3.25
1.71
1-5
1-835
2.33
2.00
2.25
2.80
2.3
1.5
2.00
2.15
2-15
2-31
2.51
2-42
2.61
2.-1
2.;
2.A
3.10
3.25
3.4*
3.03
3-32
3.73
3-73
1.97
2.01
2.51
2.71
2.93
3.16
3.41
2.93
3.16
3.41
3.65
3.98
3.26
3.57
5.
4.00
4.00
3-7
4.06
4.35
4.11
4.-9
4.52
5.29
5.69
3.9 3.99
5.68
3-99
4-64
4-33
5-01
4.70
4.64
4-71
5.01
5.46
5-85
6.33
5.09
5.45
5.-5
5.66
6.06
6.0
6.?6
7.46
5.41
6.
6.81
7-36
6.58
6.81
7
6-81
7-33
7.23
75
Z-57
9.15
9.59
10.6
9.19
9.95
10.6
11-3
12.1
9.95
10.6
11.3
10.3
11.0
11.8
12.'
13.A
11.3
12.1
13.0
14.6
15.7
16.9
16.0
1'.l
1 .
19.7
21..
1.60
1.75
2.15
2
2.77
3.01
.34
2.11
2.32
77
3.01
3-7
3.
1. 2
2.02
2.2
2.
2.72
2.55
2.79
3.07
3-21
].7
3.37
4.69
509
5- 52
.99
3.70
3.
4.2
4.
4.2
4.0
5
5
5.4
3-01
332
4.06
4-06
4.46
5.01
5.45
9.94
6.46
7.03
7.66
7-05
7.65
7.94
8.57
9.19
5.37
5.0
6.46
7.03
8.33
9.07
9-00
9.76
9.85
10.6
6.:1
71
7.41
7
9.85
106
11.3
12.1
13.0
10-6
11.3
12-1
13.0
13.9
11:3
12.1
13-0
13.9
14.9
17-0
13-9
1.
149
16-0
17.1
0-9
14-9
1.7
16.0
17-1
18.4
14.9
16.0
17.1
16.0
17.1
19.4
19.4
19.7
21.1
19.7
21.1
22.6
4-49
4.96
.
6.70
7.41
66
8.57
9.41
33
9.07
9.87
10.7
3.48
2.71
2.26
2.45
2.6
2.88
2.54
3.12
4.50 5.01
6-50
8.29
5.84
5.41
5.84
7.9
3.51 3.3
.
.
12.1
13.0
& 41
4.73
6.27
6.73
.2
.- 9
19.1
19.4
20.9
22.4
24.0
1.62 1.62
3.25
2.33
2.15
2.34
4.89
3
.92
1.40
1.51
1.6
1.41
1.97
1.00
03
6
1.00
1.10
1.21
1.32
1.45
1.11
1.22
1.35
1.49
1.65
3.
2.63
2.81
2.00
2.i4
2.30
2.46
2-64
2.00
2.46
2.64
2.53
3.03
3.02
2.13
2.3
3.25
4.26
3.3
3-25
3.0)
3-25
3.45
.'
3-73
4.56
4-59
5.24
7
3.44 3.48
.73
3.73
7
3.75
4.00
4.29
4.59
4.92
5.28
4.59
4.92
5.21
4.00
4.29
4.59
4.92
5-28
4.29
4.59
4-92
5-29
5.66
6.06
6.50
6.96
7.46
6.06
6.50
6.96
7.46
5.66
66 5.6
6.06
6.06
6.50 6.50
6.96 6.96
7.46
7.46
4.00
4.00
1.00
8.57
8-57 8.00
8-57
8.57
9.85 9.83
9.9
9.09
13.9
14.9
1.74
2.00
2.14
4-00
4.29
1..7
.02
1.62
1.1
.5
1-
1.41
1-51
1.32
.1-41
1.74
,.8
.1
1. 2
,74
1.10
1.00
1.2,
1.56
1.34
1.99
2.14
2.6
2.65
2.45
2.9
2.41
2.51
2.6)
3.02
3.02
.20
2-81
37
3.23
5.4
3.71
).02
1.4
1.00
1.6)
1.10
2.45
1.79
1.99
1.21
1.34
1.48
2.65
2.14
2.81
2.29
5.2
3.
2.05
2.6
2.01
3.02
3-23
3.23
9.46
5.71
3.
3.71
.97
3.46
3.97
4.26
4.26
A.-
4.;9
5-24
5.61
4.;6
4. 9
5-24
5.61
4.26
4-56
A--9
5.24
5.61
01
6.44
6.90
6.01
6.01
6.44
6.90
7.39
6.44
6.90
7.39
5-61
01
6-44
6.90
6.90
5.61
3.23
3.71
3.,6 3.9'
3.'
4.24
3.97 456
4.49
5-24
1-61
601
5-61
6.44
6701
6.44
6.10
7.39
7.92
6.90
7.39
.92
7.79
3.71
3.97
4.263-97
4-56
,.59
5.24
7.92
7.92
7.39
1-6)
1.79
1.98
2.10
3.7
3-97
2.4
2.6)
2.11
3.02
3-23
5.24
4-26
3.46
5.61
601
6-44
4.16
4. 9
5.24
3.71
3-97
4.26
M.7
3.97
4-26
4-56
419
3.02
3.23
3.4
4.54
7.92
A.49
9.09
9.74
10.4
4.49
9.09
9.74
10.4
11.2
4.49
9.09
9.74
10-4
11-2
7.92
0.49
9-09
9.74
10-4
7.39
7.92
92
0.49
9.09
9.74
6.01
6.44
6.90
7.39
7-92
4.89
8.49 9.74
8.00
8.57
9.09
9.74
10.4
11.2
10.4
11.2
12.0
12.8
11.2
12.0
12.9
13.1
14.7
12-0
12.8
17.1
14.7
15-8
12.0
12.9
15
14.7
15.
11.2
12.0
12.8
13.8
14.7
10.4
11.2
12-0
12.8
13.
8.49
9.09
9.74
10.4
11.2
6-90
7.39
7-92
8.49
9.09
9.19
9.85
101
11.3
12.1
12-0
12-8
13.8
14-7
15.8
13.8
14.7
15.8
16.9
15.8
174
1 .9
19.1
19.4
20.1
16.9
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11.2
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90
91
92
93
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15
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1979
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191
The instantaneous Perceived Noise Level is calculated according
to the following three step procedure taken from Reference 2.
Step 1
Convert each measured 1/3 octave band sound pressure level
in the range 50 to 10000 HZ, L
(i), that occur at any given
instant of time, to perceived noisiness
(Noys), n(i),
by re-
ference to Table 2-1.
Step 2
The Noy values, n(i),
found in step 1, are combined in the
manner prescribed by the following formula:
N = n + 0.15[E n(i) - n]
(2.1)
where n is the number of Noys in the noisiest band and N is the
total
Noy value.
Step 3
The total perceived noisiness, N, is converted into
Perceived Noise Level, L PN, by means of the following formula:
LPN= 40 + 33.3 log N
which is plotted in Figure 2.2
(2.2)
LPN can also be obtained by
choosing N in the 1000 Hz column of Table 2.1 and reading the
corresponding value of L
P
which, at 1000Hz, is identically
equal to L
PN'
The maximum value of the instantaneous LPN is designated
L
PN
.
For the case of an aircraft flyover a slightly different
max
formulation is Peak Perceived Noise Level
(L PN)
in which
case the 1/3 octave band levels are to be the peak values
attained in each band during the event, regardless of when
these peaks occur.
L
PNk
is not an instantaneous value and
-12-
140
130
-o120
z
u110
G100
S90
0
z
$ 70
60
50
4011
1
I
10
100
10000
1000
Total Perceived Noisiness, N, noys.
Figure 2.2
PERCEIVED NOISE LEVEL AS A FUNCTION OF NOYS
(from Ref.
2)
cannot be used to calculate
L PN
max
A correction may be made for the effect of pure tones in
the spectrum, which may well occur for fan engine noise.
This
correction is fairly complex, but is given on page 23 of
Reference 2.
Tone-corrected Perceived Noise Level is designated
TPN'
Approximate relationships between L
L PN=LA + 13
L
PN
=L
D
+ 6
-14-
400*
I
-1--l-
I-
I
1 0 ' "
1 W$
M.
01
and L
A
and L
D
are:
(2.3)
(2.4)
(2.5)
LD=LA + 7
p
PN
2.2 Proposed Method of Measurement of Time Invariant Sounds
Several experiments have been performed in order to evaluate
the effectiveness of the measures just described.
Serendipity Inc.
A report by
(Ref. 1) has surveyed some of these experiments,
notably those by Ollerhead
(Ref. 3),
Kryter and Young and Peterson.
Williams et al, Hecker &
Specific conclusions cannot
be summarized without detailing the conditions under which the
experiments were performed, but they generally indicate that
for sounds of constant duration there is little to choose
between A-weighted or D-weighted Sound Level
Perceived Noise Level
noise.
(LPN)
(L
or L D) or
as methods of measuring aircraft
The argument is made that there is no virtue in trying
to determine, to a high degree of accuracy, a subjective reaction that is not determinate.
A later report by Ollerhead
(Ref. 4) concludes that "despite deficiencies that cannot be
overcome by refined weighting circuits, it is clear that the
weighted sound pressure level provides a very powerful scale
for comparing the sounds of aircraft".
In Reference 5, Kryter
recommends the use of LD over LA since it weighs low frequency
sound more heavily.
L
or L may be measured using a hand held sound level
A
D
meter, whereas LPN involves a simple, but tedious, calculation
involving analysis of octave band levels; a computer is required
for repeated measurements.
could be built,
A small single purpose computer
but as far as is known an "LPN meter" does not
exist on the market. For compatibility with the introduction
of airport noise monitoring systems, the D-weighted sound level
is recommended over Perceived Noise Level as the unit for
measuring aircraft noise.
It may be argued that to return to a noise measure that
did not include the subjective effect of pure tones is a
b ackward
step.
However, there is evidence to suggest that
acoustic linings on the intake and exhaust of the engine are
-15-
particularly effective in eliminating pure tones because the
lining can be tuned to absorb a certain frequency (Ref. 6).
Thus there is still an incentive in eliminating pure tones from
the acoustic signal of the engine because it will achieve some
reduction in noise level in dB(D)
(although not as great a
reduction in noise level measured in EPNdB),
low cost.
Furthermore, Ollerhead
at comparatively
(Ref. 4) found only a
marginal improvement in subjective reactions due to the application of the tone correction to the PNL procedure.
The only
major reservation concerning the use of D-weighted sound level
is the fact that it fails to correlate as well with noisiness
for low frequency sounds (e.g. helicopter sounds) as with high
frequency sounds.
noisiness scales
This failing is common to all perceived
(Ref. 4).
Ollerhead suggests that further
experimental research is required into the perception of low
frequency harmonic noise.
It is anticipated that a solution
can be found to the problem of very low frequency helicopter
noise
(i.e. rotational noise and blade slap) through design
modifications.
-16-
2.3 Duration Correction For Flyover Noise Level
2.3.1 Effective Perceived Noise Level
In order to account for the duration effect of an aircraft
flyover a refinement has been introduced
which utilizes the
fact that annoyance appears to increase in a manner related
to the total energy of the sound received; doubling the duration of a noise is considered equivalent to increasing the level
of the noise by 3dB.
Tone-corrected Perceived Noise Level is therefore converted
into a form that approximates to its intensity and then
summed, finally being reconverted back into a decibel form.
The expression for LEPN may be written:
L
N
EPN
=
T
(
LTPN(k)/10
d/4t
10
10 log
log-t
k=0
(2.6)
where T is a normalizing time constant.
L TPN(k) is the value of LTPN at the k-th increment of time.
d is the duration of the time interval during which LTPN is
.
within a specified value, h, of L
max
These are illustrated in Figure 2.3.
The following figures are most commonly used when calculating
L
EPN
T = 10 sec.
t = 0.5 sec.
h = 10 dB
Equation 2.6 then becomes:
2d
LEPN
LTPN(k)/10
- 13
10 log
-17-
(2.7)
LEPN CALCULATION METHOD
Figure 2.3
L
-0
U
UL
C
0
z
t(1 )
t(2)
Flyover Time t, sec.
Figure 2.4
LT PN to LEPN
CORRECTION METHOD
LT PN
max
L4
Q) U)
0 0
pH7
A
,-
Flyover Time,
-18-
t,
seconds
The "lOdB-down"
cut off points serve mainly to avoid the
inclusion of a part of the history of the noise that does not
significantly affect the result; a value of L
that is lOdB
TPN
below the maximum possesses an order of magnitude lower value
of intensity, and is therefore not significant.
Equation 2.6 may be rewritten in the form:
LEPN
where t , t
o
1
=
t
'PNmax+ 10 log
10
LJTPN/10
.
10
PNmax/10(28)
T
correspond to the "lOdB-down" points.
In this
form of the equation it can be seen that the total weighted
energy is divided by the energy received from a sound that has
a square noise distribution with time
(see Fig. 2.4).
If the
energy received is less than the reference energy, then a
correction is subtracted from LTPN
;
if greater, the correction
max
is added.
Reference 2 suggests that an approximate method of determining this correction is by means of the formula:
(2.9)
D= 10 log( )
t
Where
D= the correction to be added or subtracted
from the value of
LTPN
max
d= the time interval during which LTPN is
within a specified value,
h,
of L
TPN
T= a normalizing constant.
The following values are suggested.
T= 15 sec.
h= 10 dB.
-19-
max
Equation 1.9 becomes:
D = 10 log
(2.10)
d
15
This method yields, in general, corrections that are larger
than the exact method.
2.3.2 California Noise Regulations:
Single Event Exposure Level
The State of California has introduced noise measures with
which to control the levels of noise around airports in California.
Details of the multiple event noise measures will be given in
Part 3; the single event noise measure within these regulations
is included here.
The Single Event Noise Exposure Level
(LSENE)
ways similar to Effective Perceived Noise Level.
is in some
The antilogarithm
of the A-weighted sound pressure level is integrated over time and
then converted into a decibel form, the reference duration for
time being one second.
From Reference 7, appendix D, LSENE
may be defined as:
L
SENE
L
A max
Where
+ 10 log
I
to
LA/10 dt LAmx(.1
10 A
1max
t(2.1)
ref
= the maximum A-weighted sound level.
LA
max
LA
= the instantaneous value of A-weighted
sound level.
tref
=
a reference time of 1 second.
t ,t
0 1
=
the times at which the sound level is
within at least 30 dB of the maximum
allowable level of LSEN
-20-
In the form of equation 2.11 the duration correction term compares
the A-weighted sound pressure energy to the A-weighted energy
contained in a pulse of sound with duration of 1 second and constant
level of L
.
A
The ratio of the energies is converted into a
max
decibel form.
Alternatively equation 2.11 may be written in the form:
J/6t
LSENE
Where
=
10 log
-ef
k=O
LA(k)/10
(2.12)
At
10
LA (k) = the value of L
at the k-th increment
of time.
d
=
the duration of the time interval during
which L
is within at least 30 db of
A
the maximum allowable value
of LSENE'
The formulation also shows the similarity between
LSENE and LEPN'
(See 2.6) A rough relationship between L
and L
is
EPN
SENE
given by:
L
L
SENE
EPN
- 6
(2.13)
The apparent flexibility in the cutoff times does not significantly affect the result of the calculation unless the peak
value of LA is only a few dB(A) above the cutoff value.
the energy of the flyover noise is close to the peak;
Most of
sounds more
than 10dB down from the peak contain less than 10% of the energy
at the peak.
The important consideration is that the cutoff value
should be above the ambient noise level;
if this is not so the
cutoff must be adjusted upwards to be above the ambient level.
While this is not a problem for noise from current aircraft, it
will be in future years, and requires changing the definitions for
L
SENE
and L.
EPN
-21-
2.4
Proposed Method of Measuring Flyover Noise Level
The most commonly used noise measure for aircraft noise,
L EPN,
and the California Noise Measure L SENE
both assume that
there is a 3dB increase in subjective noise for every doubling
of duration.
Little and Mabry
(Ref. 7) show a 0.6 to 3.1 dB
per doubling of duration for sounds of 1-34 seconds in duration
with a mean of 2.0 dB per doubling.
Pearson
Earlier work by Kryter &
(Ref. 8) had shown that doubling the duration of a
test sound had to be counter-balanced by reducing its level by
4.5 dB in order to maintain the same impression of disturbance,
although subsequent extension of these experiments showed from
6 to 2 dB per double duration.
In
view of this apparent mixture of results,
it
should
be noted that the 6 dB increase in noisiness per doubling of
duration applied to sounds of less than 5 seconds in duration;
for sounds of 5 to 50 seconds in duration, a 3 dB increase in
noisiness per doubling of duration is a reasonably close
approximation to the empirical data.
by Ollerhead
This is concurred in
(Ref. 4) who found that 3 dB per duration doubling
was close to optimum for aircraft sounds.
The evidence therefore points to the conclusion that
duration correction of 3 dB per double duration is generally
reasonable.
We shall propose the adoption of an aircraft noise
measure similar to the measure proposed by the California
regulations except that we shall use the D-weighted noise scale.
2.4.1 Aircraft Effective Noise Level, L
DE
We define an effective noise level measure using the Dweighted scale:
-22-
L
/10.A
LD (k)
k10
).t
=10 log --l
tref k-O
DE
t =
tref
I
integration interval, k = kth interval.
= reference time = 1 second
d = duration of sound above some nominal
background level such as LD = 80.
This is similar to the definition of LSENE except for the
use of a D weighted noise scale, and definition ofd
above a nominal level.
as time
Thus, the monitor microphones are set
at a given "breakout" level.
This measure can be used to certify new transport aircraft instead of LEPN, and it also allows construction of field
measurement equipment that can be used in real time.
Certification
limits can be established for the values at three basic
measuring points, and"runway monitor" instrumentation constructed
at similar points relative to real airport runways to measure
operational flyover noises.
-23-
2.5 Regulations for Controlling Aircraft Flyover Noise
2.5.1 Port of New York Authority Regulations
The first regulations controlling the level of flyover noise
from jet transport aircraft were established by the Port of New
York Authority in its role as landlord.
These rules are still in
effect, and are applied through the use of noise monitoring equipment at J.F.K. Airport.
Microphones are placed on the extended
runway centerline at the approximate boundary of the community
(varying between 2.8 and 7 miles from the start of roll depending
on runway).
A maximum noise level of 112 PNdB is allowable,
above which an infringement is recorded in the name of the offender.
Infringement reports are made to each airline monthly, and repeated
violations bring threat of legal suit.
Although measuring aircraft
flyover noise levels, this process is a means towards minimizing
extreme levels of community noise exposure, and the resulting
complaints or lawsuits from the community
due to this
exposure.
2.5.2 Jet Subsonic Transport Aircraft
(FAR Part 36)
The calculations for LEPN are somewhat unwieldy, and a
computer is generally required to calculate the value of LEPN
from a knowledge of the noise spectrum and its time history.
However, this criterion is important because it is utilized
presently in the Federal Aviation Regulations
(Ref. 11) which
limits the allowable noise of jet subsonic transport aircraft
which are certified after 1 December 1971.
These regulations
limit the certificated values of LEPN as measured at three
points as shown in figure
2.5.
The reference point for landing
approach is 1 n. mile from threshold;
the reference point for
takeoff is 3.5 n. miles from start of takeoff roll; the reference point for sideline noise during roll is located 0.35 n.
miles to the side of the runway for 4 engine jets, and 0.25
n.
miles otherwise.
-24-
TAKEOFF
-LTAKEOFF
ADDDR
REF
POINT, 3-5 N MI
FROM BRAKE RELEASE
AA
0.35-N MI SIDELINE
REF FOR 4 ENGINES
-A\HE
'APPROACH REF
POINT, 1 N MI
FROM THRESHOLD
FIG. 2-5
FAA CTOL NOISE REFERENCE LOCATIONS
-25-
APPROACH NOISE LEVELS
(1n.mi. from threshold on the extended runway centreline)
Ratio
100.
EPNdB
EPNdB3
I1ZU
Though EPNdB and PNdB do not precisely
relate, the PNdB limits for Heathrow
are 110 by day and 102 by night
at the defined measuring points.
90
707/320ce
80
VC 10
0 Concorde
70-
Boeing 747 delivered
from 1972 on, will be
designed to meet the
Noise Certification Standards
60-
50-
B 747
DC-8/63
110
DC-9/30
108
10
IAPPROQACH
40-
CERTIFICATION
DC-6B 727-100
105
I
30-
DC-10
Retro
0
DC-8/63
100i
-Retro
eio-
DC-9/30
20-
STANDARD
/0c1
Retro
727-100
*
95 DC-3-Retro
tfu.
10
80
70
An
0
j.. .- -1
100
200
.I
-I
L
I
300
400
500
600
700
800
900
Maximum All-up Weight-lb x 1,000
Figure 2.6
F.A.R.
PART 36 APPROACH NOISE LEVELS
-26-
(from Ref.
18)
TAKE-OFF NOISE LEVELS
(3-5 n.ml. from start of roll on extended runway centre line)
Ratio
100-
EPNIdB
EPNdB
120
Though EPNdB and PNdB do not precisely
relate, the PNdB limits for Heathrow
are 110 by day and 102 by night
at the defined measuring points.
90-
80-
70-
115
707/320c
* Concorde
0 747
19 DC-8/63
60-
Boeing 747 delivered
from 1972 on will be
727/100
g
50-
designed to meet the
Certification Standards
I1Noise
110
110 DC-9/30-VC 10
*
'707/320ci
Retro 61
727/100
I
I Retro
40105
o
O
DC-6B
08
TAKE-OFF
CERTIFICATION
STANDARD
DC 8/63
Retro
DC-9/30
Retro
30100.
.DC-10
DC-3
2095
93
.90
1080
70
601
0
I
100
200
390
400
500
600
700
800
900
Maximum All-up Weight-lb x 1,000
Figure 2.7
F.A.R.
PART 36 TAKE-OFF NOISE LEVELS
-27-
(from Ref. 18)
SIDE-LINE NOISE LEVELS
At a point on a line parallel to runway centre line
3 engines and less 0-25n.ml.
Ratio
100
more than 3 engines 0-35n.ml.
EPNdB
EPNdB
120-1
Though EPNdB and PNdB do not precisely
relate, the PNdB limits for Heathrow
are 110 by day and 102 by night
at the defined measuring points.
90.
80-
T11
Concorde
707 320c
1o
DC-8/63
108
7320c
J(CERTIFICATIONRetro
I DC-8/63
of727-100
er.
401I
DC-68
0
105
DC-9/30 00
l00
1
t
SIDELINE
STANDARD
....
&747,.:
VC-10
727-100
Retro
6DC-9/30
---- Retro
95-
0 DC-10
DC-3
90
on
706C
---- I0
100
I
- '__
200
300
-I 400
-I
S
I
I
500
600
700
800
..
- .
900
Maximum All-up Weight-lb x 1.000
Figure 2.8
F.A.R.
PART 36 SIDE-LINE NOISE LEVELS
-28-
(from Ref.
18)
The levels of current aircraft are compared to the limits
of FAR (Part 36) in figures 2.6, 2.7, and 2.8.
Exceptions to the regulations are aircraft that were in a
late state of development at the time the regulations were
adopted (such as the B-747, although Boeing agreed to meet the
requirements in 747s delivered after 1 December 1971) supersonic transport aircraft, and STOL or VTOL transports.
2.5.3 California Noise Regulations
The value of L
(s
of 11/28/70)
is
'
specified by the California regulations
SENE
Fig. 2.9
given in Figures 2.9, 2.10 and 2.11.
shows the range of positions for the measuring points for takeoffs and landings.
Figure 2.10 shows the LSENE limits for
takeoff for varying classes of aircraft as a function of this
position.
Figure 2.11 shows the LSENE limits for landing by
various classes of aircraft as a function of the position of
the landing microphone.
Aircraft of a given class must not
exceed these limits as recorded in actual operations by the
microphones.
-29-
Landing
Threshold
dL
L
I
-
-mm.I
Flight
Direction
4
-100
-.
ONME
-77..
-
&
0
Q
Point 150 fe'et inboard of
beginning of runway surface
usable for takeoff.
Microphone Locations
L -
Landing
T -
Takeoff
---
Centerline of Nominal
Takeoff or Landing
Flight Track
d L = 2500 feet to 1.0 Nautical Mile
dT = 10,000 feet to 3.5 Nautical Miles (see Figure 3a.)
Figure 2.9
SINGLE EVENT NOISE EXPOSURE LEVEL MONITORING POSITIONS
(from Ref. 9)
Curve
Aircroft Class
A
B
C
D
E
E + 3 dB
4
4
3
2
2
4
Engine
Engine
Engine
Engine
Engine
Engine
*
High Bypass Rotio Engine
Turbojet TurboFon (e.g., 707, 720, DC-8)
"Jurrbo" Turbofan (e.g., 747)
TurLofan and Arbus *(e.g.,727, DC- 10, L-1011)
Turbofon (e.g., DC-9, 737)
Business Jet.
Business Jet
,
-4
(1
6
+1
125
A
0
0
120
-S-1
I
NT-1 +
4
T
7-
110
T
-.,
I-zr-7- zz
T
105
100
..........
i#
;II
Li
-1LLI'
10
12
14
F
2ffiL
II
16
18
20
22
D T, Distance From Start of Tokeoff Roll, 1000 ft
a) Tokooff
Figure 2.10
MAXIMUM LIMITS FOR SINGLE EVENT NOISE EXPOSURE LEVEL
(from Ref. 9)
-31-
Cive
z
A;rcroft Class
4
Y
x
w
V
V+3dB
Ergne
*2,3 Eng;ne
4 Engne
3
Engine
2
Engine
4 Engine
*
Turbojet and Turbofon (e.g., 707,720,DC-8)
TurboFan (e.g., 727,737,DC-9)
"Jumbo" Tu-bofon* (e.g., 747)
Airbus Turbofon* (e.g., DC-10, L-1011)
Bus;ness Jet
Bus;ness Jet
High Bypass Rot;o Engine
8.
110
0
Cs
105
DL, Distance From Londing Threshold, 1000 ft
b) Londing
Figure 2.11
MAXIMUM LIMITS FOR SINGLE EVENT NOISE EXPOSURE LEVEL
(from Ref.
-32-
9)
2.6 Proposed Regulations for Controlling Aircraft Flyover Noise
In this section, we shall briefly outline a consistent
structure for measuring aircraft flyover noise for all kinds
of transport aircraft VTOL.
jet subsonic, supersonic, STOL, and
These measurements of flyover noise would be used in
certifying new aircraft under standard conditions and also in
airport monitoring of actual flyovers under all atmospheric
and operational conditions.
It will use LDE as described
previously as the basic measurement scale for new certification tests, and for real time monitoring in the field.
2.6.1 Q-Class Aircraft Certification Limits
The limits for noise certification should vary with aircraft gross weight to avoid penalizing the larger, more productive aircraft thereby causing two noise operations at a
reduced level instead of one operation.
It is proposed that
there should be created a "Q-class" of certification with
noise limits about 10dB lower than the standard case.
The
structure for noise limits would then look as shown in Figure 2.12
varying with gross weight as it
does presently .
A new class of
limits would be established for aircraft which choose to meet the
quieter certification requirements.
The new Q-class can be described as the next type of
aircraft for some future time period.
In the interim, there
may be a need for a set of quiet short haul aircraft of the
RTOL, STOL or VTOL types which would be required to meet these
quieter limits.
As described in reference 29, these "Q-planes"
would be allowed into a set of new "Q-ports", which are new
airports in urban areas which become acceptable to the surrounding
be
communities if they are guaranteed that only "Q-planes" would
allowed to operate there.
Aircraft which would never use Q-ports
-33-
Noise Level
10dB
Q-class
75
600
Gross Weight/1000 (lbs)
Figure 2.12
STRUCTURE FOR CERTIFICATION NOISE LIMITS
-34-
can be built to meet the normal standards without any economic or
performance penalty.
2.6.2 Measuring Points for Certification and Monitoring
Because of the wide range of operating paths possible for
CTOL, STOL, and VTOL aircraft, and because airport monitoring
equipment may have to be placed at various locations relative
to different runways, it is proposed that a range of measuring
point locations and corresponding limits be specified.
This
is similar to the present California regulations described in
2.5.3 and figures 2.10 and 2.11.
The manufacturer would be
required to demonstrate compliance under worst case conditions
with a given set of measuring points, with the full knowledge
that he will be supplying aircraft to customers who will be
required to meet these limits in varying conditions and measuring points in the field.
It is suggested that the three basic measurements
takeoff, and sideline be retained.
of approach
For the approach, the
measurement points would range from 2000 feet to 1.0 n. mile
For takeoff, they should
from threshhold along the approach path.
range from 2000 feet to 3.5 n. miles along the takeoff path.
For sideline noise, it is suggested that a standard 1000 feet
displacement line be used to monitor takeoff roll along the
runway for both STOL and CTOL, and that a circular line of
1000 foot radius be used to monitor lift
a VTOL pad.
off and landing around
Sideline noise limits should be met at all points
along the displacement and circular lines.
These measurements
lines are shown in Figure 2.13.
This report is not concerned with establishing the levels
of L
which would be specified in this structure. These should be
DE
the outcome of a political process which determines a fair and
equitable answer for all parties.
-35-
CTOL and STOL
Sideline Measurement Line
1000
1000
Sideline Measurement Line
--
0
3
VTOL
circular Measurement
Line
Figure 2.13
MEASUREMENT
LINES FOR SIDELINE NOISE
-36-
3.0 MEASUREMENT AND CONTROL OF AIRPORT NOISE EXPOSURE LEVEL
3.1 Measurement of Multiple Event Noise Level
To a large extent calculation of noise exposure is a modelling
process.
The model should predict the noise levels of individual
flyovers, and by applying corrections for the effect of durations,
multiple flyovers and time of day effect,
it
should determine the
total noisiness over time at any given point around an airport.
Models of noise exposure have generally only gone this far.
Contours have been drawn of equal noisiness and the area within
a certain contour has been used as a measure of total noise
impact.
The formulae that have been used to calculate the cumu-
lative effect of noise are the Composite Noise Rating
(CNR),
superseded by the Noise Exposure Forecast (NEF), and the Noise
and Number Index
(NNI) in England.
Each of these formulae is
described in this section of the report.
3.1.1 Composit Noise Rating
The first attempt to account for the effects of frequency
and time of day was the introduction of the concept of Composite
Noise Rating by Rosenblith and Stevens in 1952.
development of CNR may be found in Reference 17.
A history of
It is of
interest to note that determination of CNR originally involved
such factors as impulsiveness of the sound, background noise
levels, and the effect of the community's previous exposure to
noise.
dropped.
These corrections were mostly intuitive and were later
The concept of CNR has now been largely superseded by
the Noise Exposure Forecast
(NEF).
The formulation of CNR is
CNR
= (LPNmax)j
as follows:
+ 10 log [(ND)j + 20(NN j
-
12
where CNR. is for a single type of operation proJ
ducing a specific noise characteristic.
-37-
(3.1)
(L
PN
) = the maximum value of L PN for that
P
max
noise,
ND, N
DN
=
the number of day (0700-2200) and
and night (2200-0700) operations
per 24 hours.
The overall value of CNR for all classes of aircraft is:
CNR = 10 log
10 CNRg/10
(3.2)
3.1.2 Noise Exposure Forecast
With the impending introduction of LEPN as a measure in the
certification of new aircraft it was decided to incorporate it
into a new community noise measure.
Other modifications from
CNR are a change in the weighting ratio between day and night
flights and a change in the arbitrary constant in order to
make NEF numerically significantly different from CNR.
The
formulation is:
NEF
=
(LEPN j + 10 log [(ND)I + 16.67 (NN )j
- 88
(3.3)
where NEF. is for a single type of aircraft j pro3
ducing a specific noise characteristic.
(L
). = the value of L
for the type of
EPN J
EPN
aircraft j.
(N ) .(N ). = the number of day and night
DJ
N3
operations, as for CNR.
The overall value of NEF for all classes of aircraft is:
I10 NEF/10
NEF = 10 log
1
An indication of response or land use descriptions for values of
-38-
(3.4)
NEF is as follows:
NEF(30
Some noise complaints are possible and
noise may interfere with some activities.
NEF=30-40 Individual reaction may include vigorous
repeated complaints, and concerted group
action is also a possibility. Construction of homes, schools, churches, etc.,
should not be undertaken without a complete analysis of the situation.
NEF)40
Serious problems are likely.
No activity,
nor building construction should be
carried on without a complete analysis of
the situation.
3.1.3 Noise and Number Index
Noise and Number Index was developed in 1961 to relate the
noise levels around Heathrow Airport, London, to the degree of
annoyance.
The formulation is:
NNI = LPN4 + 15 log N - 80
(3.5)
where LPNM is the energy mean of the maximum values
of LPN'
N = the number of flights in a given period
(one day or one night).
The frequency correction is equivalent to 4.5 dB increase
in NNI for every doubling of the number of operations, which
is heavier weighting than most other noise measures.
recent research
heavy.
More
(Ref. 18) indicates that this weighting is too
Reference 19 suggests that a correction may be made in
order to produce an expression for NNI that applies to a 24 hour
period.
It is:
-39-
NNI = 10 log ( 10
NNI D /10
(NNI N +17)/10 ,
(3.6)
+ 10
where NNI
and NNI are the values determined for
D
N
for day and night respectively.
3.1.4 Noise Pollution Level
A recent attempt has been made to produce a system of noise
measurement that can be used for all types of noise (Ref.20).
The formulation is:
L
NP
=PL + k aeq
(3.7)
is the "energy mean" of the noise level
where L
L over a specific period.
is the standard deviation of the instant-
(T
aneous level considered as a statistical
time series over the same period.
k is a constant provisionally given the value
The noise level L is
2.56.
to be mea-
sured in a scale adequately related to
subjective noisiness, e.g., dB(A), dB(PN),
dB(TPN).
Thus:
r N
Leq = 10 log
Z.,(n
Li/10
10
)/
(3.8)
N]
where L. is the noise level of the ith interval.
1
n.
1
is
the number of times that L.
1
occurs.
N is the total number of measurements.
-40-
CT
I/NJ
n (Li-
=
1/2
(3.9)
where L is the arithmetic mean noise level.
The index LNP generates a rate of increase of exposure
level with number of increases that is steeper than the 3 dB
per double number given by the simple concept of energy
summation; the relationship is actually nonlinear, growing
more steeply
in the middle range of occurrences.
3.1.5 Hourly Noise Level
(California) L
The Hourly Noise Level
(L
HN
) is the basic measurement used
for computing the daily Community Noise Exposure Level (LCNE)
at a given station.
L
is the average value on an energy basis
of the A-weighted sound level over a given hour
L]SENE + 10 log n - 35.6
10
30
LHN' 10 log
where LSENE is
hour;
(3.10)
the energy average LSENE during the
n is
the total
number of single events
(flights) during the hour
3.1.6 Community Noise Equivalent Level
(California) LCNE
The total noise exposure for a day is specified by the
Community Noise Equivalent Level, LCNE,
in dB, and may be
expressed by:
LCNE
10 log
1I
(LHN) D(i)/o 3
where
(L
(10
+3
(LHNEj)/JO 9
10
(LHNN(k/10
+10N10k)
)D are the hourly noise levels for the
-41-
(3.11)
period 0700-1900 hrs.
(LHN)E are the hourly noise levels for the period
1900-2200 hrs.
)N
(L
are the hourly noise levels for the period
2200-0700 hrs.
If the values of
are approximately the same then the
LSENE
expression for LCNE is:
LCNE
=
LSENE + 10 log ( ND + 3 NE + 10NN)
-
49.4
(3.12)
where LSENE is the energy average LSENE during the
24 hours.
N
D
is the total number of flights during the period
0700-1900.
NE is
the total
number of flights during the period
1900-2200.
NN is
the total
number of flights
during the period
2200-0700.
The annual value of LCNE is:
1s L
(i)/10
Annual LNE = 10 log (
where LCNE (i)
is
the daily value of LCNE'
-42-
(3.13)
3.2
Proposed Method of Measuring Airport Noise Exposure Level
3.2.1
Hourly Noise Exposure Level
Hourly
1 NEH
=
10 log [0
where n = no.
(LDE -LDB
]
(3.14)
of operations in the hour.
This is similar to LHN in California, except background
noise level, LDB,. appropriate to the time of day is introduced.
It performs energy averaging over the multiple aircraft operations within the hour, as perceived at some listening point
in the community.
Rather than measure actual background levels
at these measuring points, it is suggested that a nominal
background level, which varies with the time of day, appropriate
for a residential area be used.
For example, the following
background levels are suggested:
Hours 0700-1900, LDB = 75dBD (
81 PNdB)
Hours 1900-2200, LDB = 70dBD (
76 PNdB)
Hours 2200-0700, LDB = 65dBD (
71 PNdB)
This varying background level is intended as a replacement
for the arbitrary weighting of flights by time of day used in
other measuring systems for noise exposure.
If actual background
levels are used, this measure relates noise exposure to
"intrusive" noise.
-43-
3.2.2
Daily Noise Exposure Level
Daily LED
10 log
[124
L
/ 10
lOJH
(3.15)
The daily noise exposure is then simply the energy
averaged sum of the hourly noise exposure values.
This system introduces background levels as a factor
in measuring community noise exposure.
Because background
levels are subtracted, the numerical values will be significantly smaller than other measures (except NEF which
subtracts 88),
and they represent noise above background noise,
or intrusive noise.
As quiet V/STOL vehicles are introduced,
this background level becomes a far more significant factor
than it is presently.
It is possible for future quiet
helicopters to stay below background levels.
This measure-
ment scale would then provide a zero LNED value in the surrounding communities, quite appropriate to the actual noise
exposure.
-44-
3.3
Regulations for Controlling Airport Noise Exposure Level
At present the question as to who is going to control the
noise exposure levels around airports has not been resolved.
While the FAA has accepted responsibility for certification of
aircraft with respect to noise (FAR Part 36),
it has declined
responsibility for noise certification of airports or establishing
noise exposure levels for surrounding communities.
In October 1972, Congress passed the Environmental Noise
Control Act charging the Environmental Protection Agency with
carrying out studies of "implications of identifying and
achieving levels of cummulative noise around airports" and
"additional
measures available to airport operators and local
governments to control aircraft noise".
Recommendations
from EPA will be considered in a hearing held by the FAA.
It will be interesting to see the results of this activity.
In the interim, the State of California has made a serious
attempt to control airport noise, and various airport operators
are developing their own methods of control.
desirable
It would be
to establish a common system of controlling air-
port noise exposure within which these various parties could
operate.
3.3.1 California Airport Noise
A fundamental concept of the California Noise Regulations
is that of a 'Noise Impact Area' which is the direct equivalent
of the area contained within a certain NEF contour.
The major
differences are that the 'Noise Impact Area' calculation uses
L CNE
instead of LEPN and that there are different weightings for
daytime, evening and nighttime flights.
A requirement of the regulations is that the 'noise impact
area', as applied to residential areas must be zero; that is,
the noise exposure for a residential area must be less than a
-45-
given value.
Thus the regulations do not attempt to minimize the
total noise impact, but rather to control the maximum noise
exposure level that any residential area could be subject to.
Like other regulatory systems which concern people, the regulations
are designed to protect people from the worst excesses of the
disturbance, rather than minimizing the disturbance itself.
The maximum noise levels which determine the noise impact
area for various airports and time periods as promulgated by the
California regulations dated November, 1970, are as follows:
a) For proposed new airports, or military airports being
converted to commercial use, the value of LCNE is
65 dB.
b) For existing civilian airports with less than 28000 air
carrier operations, and no four engine turbojet or
turbofan operations, the value of LCNE is 70 dB until
1986, and 65 dB thereafter.
c) For other existing civilian airports, the values of
LCNE proposed were:
Effective date of regulations to December, 1975 80 dB.
Jan. 1976 to Dec. 1980
-
75 dB
Jan. 1981 to Dec. 1985
-
70 dB
Jan. 1986 and thereafter
-
65 dB
One should note that the relationship between LCNE and NEF
is roughly:
LCNE w NEF + 33
-46-
(3.16)
3.4 Proposed Regulations for Controlling Airport Noise Levels
3.4.1 Limits on Hourly and Daily Noise Exposure Level
To control the noise caused by airport operations, it
is proposed that airport noise monitoring schemes be adopted
which place microphones at selected locations around the airport.
These locations would normally be residential areas near the
airport which are felt to experience some degree of noise
exposure from the airport operations.
The microphones would
record hourly and daily Noise Exposure Levels as described in
An annual "energy averaged" value of
the previous section.
these measures can also be computed as a running average value
over the last 365 days.
It is proposed that federal limits be established for
these average annual values of hourly and daily noise exposure
levels which may be imposed by airport operations on any residential
community.
As the average annual values approach these limits,
the airport operator would be held responsible for controlling
the frequency and type of aircraft operations such as to remain
within these limits.
given airport are
If the long term forecasts of demand at a
high, there will be pressures on the airport
operator to build another airport or Q-port to serve the region,
and pressures on the aircraft operators to use quieter vehicles
at that airport.
In the event that communities are already exposed to noises
above these limits, it is proposed that a compensation scheme be
established.
A noise tax can be imposed on all takeoff and
landing operations for the noise they actually make as measured
by the runway monitor microphones.
The funds thus raised can be
paid back to the"overexposed" communities based upon the exposure
actually recorded by their monitors.
-
47
-
The levels of tax can be
adjusted to raise the funds required to meet the
compensation levels agreed by the a irport operator and the
communities.
This last process would be managed by local
political processes with the "dollar per decibel" rates
decided by federal legislation.
These control methods are only possible with the
type of measurements recommended by this report.
It is
important that a consistent set of measurements of this nature
be established on a national scale.
-48-
4.0 MEASUREMENT OF TOTAL COMMUNITY NOISE IMPACT
4.1 Measurement of Community Noise Impact
4.1.1 Footprint Area - NEF
Recently, a common method of defining noise impact has
been to describe it as the footprint area within a given Noise
Exposure Forecast (NEF) contour.
This method graphically
describes the effect of change of flight frequency and changes
in noise level of individual flyovers.
When NEF contours are
plotted on a map that shows population density the importance
of excluding high density areas from the noise impact area can
be seen, but it is not quantified.
It is important in estimating noise impact that NEF be
calculated using operational rather than certification levels
of noise from aircraft.
The certification levels are rarely
met in practice and a NEF footprint calculated using these
values may be quite different from the actual footprint.
The footprint area within a given contour is directly
proportional to the strength or intensity of the noise source.
If one assumes that subjective annoyance varies as any power of
the intensity of received sound, one can show (Ref. 27) that
total subjective annoyance summed over a uniform population
density of listeners within the contour also varies directly as
the intensity of the noise source.
Under these assumptions,
we have total community annoyance varying directly as footThis suggests use of
print area.
footprint area to measure
total community annoyance as a measure for total community
noise impact.
This will be developed in section 4.2.
4.1.2 Total Community Annoyance Measure
(TCAM)
A community noise impact measure in which the sensitivities
of different areas is implicit was proposed by Boeing Vertol
(Ref. 24).
The measure is called Total Community Annoyance
-49-
(TCAM) and is given by:
Measure
TCAM = Reference Area
L
[LEPN
- (AA)
(4.1)
dx dx
1
where (AA) is the Annoyance Awareness, which is a function of
population density and activity for a given area.
The question
arises as to whether the tradeoff between noise level and area
correct.
In this formulation doubling the area subject to a given
noise level doubles the value of TCAM, which is reasonable.
But if the area is kept constant, the level will also have to
be doubled
(e.g., from LEPN = 80 to LEPN = 160) to achieve the
same doubling of TCAM.
This is clearly not reasonable, which
suggests that the tradeoff is incorrect.
4.1.3 Community Sensitivity Weighting - W
Another community noise impact measure, which does appear
to make the right tradeoff between noise level and number of
people annoyed, has been developed by Tracor, Inc.
(Ref. 25).
This is the Community Sensitivity Weighting (W),
W = fp(x,y)N(x,y)
dxdy
where p(x,y) = population density
(4.2)
N(x,y) = "effective" noy value
L
= 10
-40
EPN
33.2
/
S = area covered by the community.
In the Tracor formulation, there is a further correction for
the effect of a large number of flights over a short period,
called the "dwell" effect.
-50-
Here the community impact is measured in "people-annoyance".
The annoyance scale is measured in "noys" which vary as the
square root of sound intensity levels above L EPN= 40.
4.1.4 Aircraft Sound Description System
The Office of Environmental Quality within the FAA has
recently proposed a method of describing noise impact called
ASDS
(Aircraft Sound Description System, Ref. 26).
It uses
the footprint area within the 100 EPNdB contour as a measure
of noise impact.
exactly 20 seconds
Each takeoff or landing is assumed to take
(or 1/3 minute),
and an attempt is made
to use actual operational noise levels from aircraft rather
than certificated
levels.
For example, a B727 at 150 knots is assumed to have a
given contour and footprint area of size x under actual operating and atmospheric conditions.
If n operations of this nature
occurred at an airport, the footprint area is summed and then
divided by three, and the result is declared to be a noise
impact of n.x) with "dimensions" of acre-minutes.
Notice that the assumption of 20 seconds per operation
produces the factor of 1/3, and allows one to arbitrarily give
this measure the dimension of time.
measure
In actual fact, this impact
(ASDS) can be viewed as a simple summation of the acres
of footprint area of a number of multiple operations, which is
then divided by three.
This acreage value turns out to be
identical to the acreage within the NEF=12 contour
(see Appendix
A) so that one can write:
3.(ASDS) = Footprint area
for NEF = 12
Viewed in this way, ASDS is simply a footprint area
NEF contour.
for an
Because of the use of overlay charts and standard
-51-
footprint areas, it is easier to calculate manually than the previous NEF methodology. (See figure 4.1)
This method may be used by people who are not acquainted
with details of the subjective effects of aircraft noise, and
does not require a computer for the determination of the value of
acre-minutes.
As such it is a convenient and easily
understood
method of describing aircraft noise impact on communities.
However, it is also important that this measure should reasonably correlate with actual subjective reaction to a given noise
impact.
In the calculation of the number of acre-minutes of
noise impact, the population distribution or land use is apparently not considered.
Even if overlays are used, so that popula-
tion distribution within the 100EPNdB contours can be examined,
it is difficult to evaluate the effect of frequency.
The com-
munity just outside a 100 EPNdB contour would not be considered
to be subject to noise impact, however high the frequency might
be; a community just inside the 100 EPNdB contour would be
considered to be impacted by noise, even if there is only 1
flight a day, &
would be given on equal rating of impact
compared to another community lying just inside the 110 EPNdB
contour. Also the assumption of an arbitrary exposure time of
1/3 (or 1/4) minute is not valid at all points in the impact
area.
For these reasons, the value in 'acre-minutes" is an
inaccurate measure of community noise impact.
-52-
90-
SAMPLE
HISTOGRAM
Figure'4.1
EXAMPLE OF CALCULATION OF ASDS
-53-
(Acre-Minutes)
Proposed Method of Measuring Community Noise Impact
4.2
The following section deals with a proposal to
determine noise impact as outlined in the introduction.
Community Annoyance Number
4.2.1
For measuring the overall impact of aircraft operations
on the community, we define a number called the Community
Annoyance Number (CAN) which has the dimensions of "peopleannoyance".
This unit is a development of a similar annoyance
measure for single events used by Tracor, Inc. (Ref. 21).
The unit is defined as:
CAN
where
(4.4)
(x,y)-M(x,y) dx dy
=
(x,y) is population density at point (x,y)
M(x,y) is the Annoyance Number, akin to the
noy and a measure of annoyance caused
by multiple noise events above a
background level.
A is the area
within which the aircraft
noise is above the background noise.
The noy was originally defined as a unit
of annoyance for
which a person subjected to a noise corresponding to 2 noys was
twice as annoyed as when he was subjected to 1 noy.
The para-
meters of the original definition took 40 dB at a frequency of
1,000 cps
as a quiet level for reference, and assumed that
annoyance varied as the .3 power with noise levels above this
reference (Reference 22, 23).
-54-
Here we shall change the reference level to background as
measured on a D-weighted scale and retain the .3 power assumption.
We shall also assume that the effect of multiple events can be
summed on an energy basis.
For a single aircraft operation:
CAN =
(xy).N(xy) dx dy
where N(x,y)
(4.5)
= a modified noy based on the intrusive
noise at point
(x,y)
A = area outside of the airport boundary
(x,y) = a point location
The modified
noy,
N(x,y) may be defined as:
LDE (
or
N(x,y)
=
N(x,y)
=
10
y) - L B
x' )
(4.6)
33.2
10\
(
10
/).3
where K = Kth increment of time
LDE = aircraft effective noise level as dedefined in section 2.4.1
LDB = background noise level
This measures the total impact in "people-annoyance" for a
given aircraft operation at a given runway under varying takeoff or landing profiles, paths or procedures.
It is also useful
in comparing the impact of a given aircraft on different runways
of a given airport.
-55-
define a "Multiple
For multiple aircraft operations we can
and daily periods.
Annoyance Number" for both hourly
.3
=
(x,y)
where
Since
%EH
(4.8)
10 (LE(x0Y)- LDB(x Y))
n = number of operation in the hour.
=
10 log
(4.9)
B10
36DE00
Then, the hourly community annoyance number CAN
(x') 'I,fl
CAN
x'y)- d
H
dy(4.11)
CANH
This measures the total impact in people-noys for an hourly
operation of aircraft on a given runway.
It is a useful measure
for operating a preferential runway system to minimize the noise
impact on the surrounding region under varying wind conditions.
For longer term planning, it is necessary to define a daily
community annoyance number, CAND
-56-
CAND
=
(x,y).MD(xy).dx dy
MD(x ,Y)
Where
24.10 LNED (x,y)/10 - .3
(4.12)
(4.13)
This measures the total impact in people-noys for a day or
an average day as forecast for a runway, or set of runways. It
may be used as a measure for siting a new runway, or airport,
and for assessing the benefits from retrofit of nacelles or
engines to existing aircraft.
This measure for community noise impact is consistent
with the measures proposed for aircraft and airport noise.
It introduces population density and background noise level as
variables which are essential in measuring community noise
impact for a given airport.
It has the
"people-annoyance" for impact.
dimensions of
A doubling of the value of CAN
will indicate either that twice as many people are being
annoyed, or that twice as much annoyance (measured in noys) is
being imposed on the same people.
Operational procedures such
as the power cutback will not substantially change this measure
of noise impact.
The measure may be computed in real time
from community noise monitoring systems and used to direct
preferential runway operations throughout the day.
-57-
5. 0 SUMMARY REVIEW
The proposed system of aviation noise measurement and
control may be briefly summarized by listing the following
items.
5.1 Measurement of Aircraft Flyover Noise
Use L
D
as a scale for measurement of noise level in
order to be compatible with monitoring hardware.
Adopt a 3 dB
per double duration correction with a nominal breakout level
such as 80 dB(D) to define an "Aircraft Effective Noise Level,
L DE
to measure flyover noise.
Abandon the measurement of
"perceived" noise.
5.2 Regulation of Aircraft Flyover Noise
Adopt a system of noise limits measured by LDE for both
certification and operational flyover noises which vary with
gross weight of vehicle.
Adopt a class of "Q-limits" for
quiet aircraft for urban short haul service which new aircraft
designs may elect to meet, and which new airports called "Q-ports"
may elect to require for operations.
Adopt a range of measuring points for landing, takeoff, and
sideline to accomodate CTOL, RTOL, STOL, and VTOL aircraft, and
varying airport monitor locations.
-58-
5.3 Measurement of Airport Noise Exposure Level
Using "Aircraft Effective Noise Level, L DE"
above nominal
levels of community background noise for daytime,
evening, and
night operations, adopt energy averaged measures for hourly
and daily "Airport Noise Exposure Level, L NE".
These can be
recorded and computed by noise monitoring equipment for
various locations in surrounding communities.
5.4 Regulation of Airport Noise Exposure Level
Adopt limits on the annualized value of hourly and daily
noise exposure levels which may be experienced by any community
in the nation as recorded by monitoring equipment.
The air-
port operator will be responsible for controlling frequency of
operations to remain within these limits through quotas, curfews, and the supply of additional airport capacity for the
region.
Adopt a compensation scheme for communities in the event
that these community noise exposure limits are exceeded.
Federally established "dollar per decibel" rates will determine
funds to be paid for noise over-exposure as recorded by
community noise exposure monitoring equipment.
These funds will
be raised by noise fees to be paid by aircraft operators based on
actual flyover noise recorded by the airport runway monitors.
-59-
5.5 Measurement of Total Community Noise Impact
Using "Airport Noise Exposure Level, LNE" adopt a
new measure called "Community Annoyance Number, CAN" to determine the impact of noise operations over time and population
in the surrounding communities.
of "people-annoyance".
This measure has the dimensions
It can be computed in real time using
the community noise exposure monitors, and used to determine
preferential runway procedures.
Longer term forecasts of
CAN may be used for siting new runways or airports, and for
determining the benefits from changes in aircraft operational
procedures or noise retrofit changes at a given airport.
-60-
I
__
-Wfflm
INIIONO___- -- "INit00--
REFERENCES
1.
"A Study of the Magnitude of Transportation Noise Generation
and Potential Abatement", Volume II.
Serendipity, Inc.
1970.
November
Report OST-ONA-71-l.
2.
"Aircraft Noise Evaluation", FAA Report No. FAA-No-68-32.
September 1968.
3.
Ollerhead, J.B., Subjective Evaluation of General Aviation
Aircraft Noise, FAA No-68-35, April 1968.
4.
Ollerhead, J.B., An Evaluation of Methods for Scaling Aircraft Noise Perception. NASA CR-1883 October 1971.
5.
Kryter, K.D., "Annoyance" in Transportation Noises
Chalupnik) Washington U. Press 1970.
6.
Feiler, C.E. et al "Fan Noise Suppression" Aircraft Engine
Noise Reduction Conference May 16-17, 1972. NASA SP-311
7.
Little, J.W., Mabry, J.E. "Sound Duration and its Effect
on Judged Noisiness" Journal of Sound and Vibration (1969)
9 (2) 247-262
8.
"Some Effects of Spectral
Kryter, K.D., Pearsons, K.S.
Content and Duration on Perceived Noise Level" Journal of
the Acoustical Society of America , Vol. 36, 1964.
9.
"Supporting Information for the Adopted Noise Regulations
for California Airports" Report No. WCR 70-3(R) Wyle
Laboratories January 1971.
(ed.
10. Anon Automatic Aircraft Noise Monitoring System General Radio
Preliminary Proposal Q 039.
11. "Federal Aviation Regulations, Part 36. Noise Standards:
Aircraft Type Certification", FAA FAR Volume III part 36,
November 1969.
12. Metzger, F.B., Foley, W. M. STOL Aircraft Noise Certification
- A Rational Approach SAE 700325 April 1970.
13. Anon Conference on STOL Aircraft Noise Certification FAA
No-69-1 January 1969.
-61-
14. Lowson, M.V. "Noise Radiation from V/STOL Aircraft"
International Council of the Aeronautical Sciences Paper 72-22
September 1972.
15. Anon Community Reaction to Airport Noise
CR-1761 Vol. I. 1970.
Tracor Inc. NASA
16. Vittek, J.F.
"Airport Noise Control" to be published in
Journal of Air Law and Commerce.
17. Galloway, W.J., et al,
"Noise Exposure Forecasts: Evolution,
Evaluation, Extension and Land Use Interpretations", FAANo.-70-0, August 1970.
18. "The British Airports Authority:
1971", BAA July 1971.
Report and Accounts 1970-
19. "Community Reaction to Airport Noise", Volume I, Tracor, Inc.
NASA CR-1761, July 1971.
20. Robinson, D.W., "Towards a Unified System of Noise Assessment"
J. Sound Vib (1971) 14(3), 275-298.
21. Patterson, H.P. Preliminary Evaluation of the Effect of a
Dynamic Preferential Runway System Upon Community Noise
Disturbance, Tracor Inc. NASA CR-12581 N72-20250.
22. Stevens, S.S., "The Measurement of Loudness" Journal of the
Acoustical Society of America Vol. 27 No. 5, September 1955.
23. Stevens, S.S., "Calculation of the Loudness of Complex
Noise" Journal of the Acoustical Society of America Vol.28,
No. 5 September 1956.
24. Stepniewski, W.Z., Schmitz, F.H., "Noise Implications for
VTOL Development", SAE 700286, April 1970.
25. Patterson, H.P., et al "Preliminary evaluation of the effect
of a Dynamic Prederential Runway System Upon Community Noise
Disturbance" N72-20250, NASA CR-125821
Tracor, Inc., Feb.
1972.
26. Anon Aircraft Sound Description System
FAA Draft Order 7040
27. Simpson, R.W., iays,A.P., "The Relationship between Total
Community Annoyance and Noise Intensity", FTL Technical
Memo 73-1, January 1973.
-62-
28. Hwoschinsky, P.V., Factors in Aircraft Noise Generation
and Transmission. MIT Flight Transportation Laboratory
Technical Memorandum 72-2.
29. Simpson, R.W., (editor), Summary and Recommendations NASA/MIT Workshop on Short Haul Air Transportation, FTL
Report R71-4, October 1971.
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SELECTED BIBLIOGRAPHY
Blumenthal V.L., et al Summary, Noise Reduction Research
and Development Boeing Company Report Nov. 1971.
Sternfeld,H., Acceptability of VTOL Aircraft Noise Determined by Absolute Subjective Testing. NASA CR-2043
June 1972.
Clarke, F.R., Kryter, K.D., The Methods of Paired Comparisons and Magnitude Estimation in Judging the Noisiness
of Aircraft NASA CR-2107 August 1972.
Clarke, F.R., Kryter, K.D., Perceived Noisiness Under
Anechoic, Semi-Reverberant and Earphone Listening
Conditions
NASA CR-2108
August 1972.
Johnston, G.W., V/STOL Community Annoyance due to Noise,
Proposed Indices and Levels University of Toronto
UTIAS TN-177.
Hays, A.P., Aircraft Noise Criteria MIT Flight Transportation Laboratory Technical Memorandum 72-3
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APPENDIX A
The Relationship between ASDS and NEF Footprint Acreage
Suppose the acreage within the L EP=100 contour for an
j
aircraft/operation of type
is given by A. .
From Reference 28,
we know that this area is proportional to the source power, or
source intensity I .;
oD
A.
j
=
k.I
(A-l)
.
oJ
i.e. doubling the source intensity by flying two aircraft
simultaneously would double A., or double the intensity at any
J
point on the ground, (or raise L EPN. at that point by 3dB).
In constructing NEF for the case where aircraft fly the
operations serially instead of simultaneously, an assumption
has been made to "energy average", or to simply sum the effect
as though all the operations took place simultaneously.
For
n. daytime flyovers, if we measure NEF. at any point:
J
J
+ 10 log (n.) -88
= LEPN
J
EPNJ
NEF
or
NEF . + 88 = L
.
+ 10 log
(A.2)
(n.)
(A.3)
EPNJ
J
If we unlog this expression to measure intensity directly,
we obtain:
3
/10 + log
L
(NEF. + 88)/10
10
= 10 EPNj
L
= n.. (10 EPNj
J
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(n.)
(A.4)
/10
This states that the intensity measured at the given point
for a single flyover is
That is,
increased n. times by the NEF calculation.
J
it is equivalent to increasing source strength n. times,
and this would result in the footprint area for any given intensity
level being increased n. times from A.l.
J
Therefore, the footprint area for a level where NEF+88 = 100
would be n. times the footprint area for LE.
= 100;
J
EPNj
AF
NEF=l2
=
n..A.
(A.5)
j
3
Now, the value of ASDS as given in acre-minutes
ASDS
-.n..A.
3 j 3
=
Therefore, for n
is:
(A.6)
daytime operations by aircraft type
j:
3. (ASDS) = ANEF=l2
(A.7)
Similarly, if there are also nk operations of aircraft
type k the summation occurs at the energy or intensity
level of equation A.4.
(NEF + 88)
i.e.
Thus,
L./10
= n..(10
10
j
EPNj
L
. (10 EPNk
) + n
/10(A8
k
the equivalent source strength is ihcremented pro-
portionally to the source strengths of each flyover, or the
footprint areas are additive.
We can now state the following:
"For daytime operations, the value of the acreage within the
NEF=12 contour is three times the value of ASDS as expressed in
acre-minutes".
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(A.8)