PRESENTASI BasicNoiseCalculations

Virginia Tech - Air Transportation Systems Laboratory

CEE 4674Airport Planning and Design

Antonio A. TraniJulio Roa

Sample Airport Noise Computations


Topics Covered

Calculating SEL (Sound Exposure Level) for single flyover events

Calculating Equivalent Steady Sound Levels (Leq) Applicable over longer periods of time

Calculating Day-Night average sound levels (LDN) Leq corrected for night effects (night events are

weighted more than day events)

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Sound Exposure Level of Single EventsCalculating Sound Exposure Level (SEL)

3


Measuring Single Flyover Events

4

Location of Noise Meter

Sound Pressure Level (dBA)

Time (seconds)

Instruments can Record SPL every Second (slow

or fast mode)

Sound Exposure Level (SEL)

IntegrateNumerically

(Using Excel / Matlab)



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Time (seconds)

Instruments can Record SPL every Second


IntegrateNumerically

(Using Excel / Matlab)

LE = 10log1t0

10L(t )/10 dtt2

t1

LE = Single event noise level (dbA)L(t) = Instantaneous Sound Pressure Level recordedt0 = reference timet1,t2 = times used to perform the numerical integration

In Practice we usea summation to compute

the value of LE



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LE = 10log1t0

10Li /10ti=1

N

LE = Single event Sound Exposure Level (SEL) (dbA)Li = Instantaneous Sound Pressure Level recorded at discrete intervals of timet0 = reference timet = is the delta time interval (typically 0.5 to 1 seconds)

LE = 10log1t0

10L(t )/10 dtt2

t1

LE = Single event Sound Exposure Level (SEL) (dbA)L(t) = Instantaneous Sound Pressure Level recordedt0 = reference timet1,t2 = times used to perform the numerical integration

Numericalapproximation

of SEL

Sound ExposureLevel (SEL)


Numerical Example # 1: Single Flyover

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Sound Exposure Level (SEL) calculation

t1 t2

LAmax

LAmax-10 db

A319 landing event in recorded at PUJ in 2012


Sample Single Flyover Event(Airbus A319 Landing at Punta Cana)

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Calculation using all values of SPL dbA

recorded

Highest Valueof SPL recorded

(known as LAmax)in Casela 240 instrument


Sample Single Flyover Event(Airbus A319 Landing at Punta Cana)

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Calculation using data from LAmax to LAmax -10 db

Highest Valueof SPL recorded

(known as LAmax)in Casela 240 instrument


Observation

The solution of SEL calculated using the full SPL history trace recorded was 93.42 dBA

The solution of SEL calculated using the time interval between highest value of SPL recorded and Lamax -10 dbA was 93.23 dBA

The small difference indicates that considering the time range of values with the peak signal (LAmax and LAmax -10 dBA) is a very good approximation

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Measuring Average Sound Levelsover a Long Period of Time

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Equivalent Sound Level (Leq)

Measures the equivalent sound level over a longer period of time

Used to measure noise over a long time Applications:

Ramp noise at the airport Runway operation noise etc.

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Equivalent Steady Sound Level (Leq)

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Leq = 10log1T 10

Li /10ti=1

N

Leq = Equivalent steady sound level (dbA)Li = Instantaneous Sound Pressure Level recorded at discrete intervals of timeT= time period to measure Leqt = is the delta time interval (typically 0.5 to 1 seconds)

Virginia Tech - Air Transportation Systems Laboratory 14

Equivalent Steady Sound Level (Leq)Numerical Example# 2 : Ramp Noise

Data capturedat PUJairport

Data sampledevery second


Equivalent Steady Sound Level (Leq)Airport Ramp Data

Aircraft arrival



Aircraft arrivalto ramp

Shown the recorded valuesbetween 540 to

630 seconds

You want the completearea under the SPL curve

Soun

d Pr

essu

re L

evel

(dB

A)

Time of Event (seconds)


Soun

d Pr

essu

re L

evel

(dB

A)

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Approximate areaunder the SPL curve

is the sum of the rectangles

Time of Event (seconds)

t = 1 second

t


Equivalent Steady Sound Level (Leq)Computations using Excel

Calculations of

10Li /10

LE = 10log1T 10

Li /10ti=1

N


Equivalent Steady Sound Level (Leq)Computations using Excel

Value of Leq

Thousands of recordings

at PUJ airport

LE = 10log1T 10

Li /10ti=1

N

T=2984 seconds

t = 1 second


Equivalent Steady Sound Level (Leq)Punta Cana Data

Leq value = 78.89 dBA


For Discussion

The approximation of the area under the curve looks very crude using rectangles

The method shown uses a rectangular integration method employing the actual observations as the basis for the height of each rectangle

Can you improve the solution? Discuss other numerical methods

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Correcting Sound Levels for Night EventsCalculating Day-Night Sound Level (LDN

or DNL)

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Converting from SEL to Day-Night Averages

With known values of SEL for each aircraft operations we can piece together a series events throughout the day to estimate the total day-night average sound levels (DNL) due to aircraft operations

However: Flight operations at night need to be corrected by an

empirical annoyance factor

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From Sound Exposure Level to Day-Night Level

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Sound Pressure

Level (dBA)

Time (seconds)

Background noise at the location can be extracted by readings made during periods of time with no aircraft operations

Single Flyover

Background noise

Average Steady Sound Level(Leq) - Requires further Integration

0 86,400

You know howto calculate SEL now

for these events


Day-Night Average Noise Metric (DNL)

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Time (seconds)

LDN or DNL is computationally similar to Leq However, Ldn includes correcting nighttime

operations (10 PM to 7 AM) by a factor of 10 dBA

Background noise

Day-Night Average(Ldn) - Requires further Integration

Airport Planning and Design (Antonio A. Trani)

Numerical Example

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Airport Planning and Design (Antonio A. Trani)

LDN = 10log1T 10

(SELi+W )i /10

i=1

N

LDN = Day-night Sound Level (dbA)SELi = Sound exposure level associated with the ith flyoverT= Reference time (86,400 seconds in 24 hrs)

The formula shown only accounts for the noise generated by aircraft flyovers

If you want the contributions of ground vehicles and other ramp noise you need to add those noise sources

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Airport Planning and Design (Antonio A. Trani) 28

Airport Planning and Design (Antonio A. Trani) 29

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PRESENTASI BasicNoiseCalculations