aircraft noise - an environmental perspective

8/3/2019 Aircraft Noise - An Environmental Perspective

http://slidepdf.com/reader/full/aircraft-noise-an-environmental-perspective 1/2

What is Noise?

The words ‘noise’ and ‘sound’ both relate to hearing and can be usedinterchangeably. The difference is we typically refer to ‘sound’ whendiscussing something pleasant such as music, and ‘noise’ when discussingsomething unpleasant, unwanted, or undesired. When aircraft fly overheadat low altitudes, many people consider it annoying and refer to what theyhear as “noise.” This “noise” can interrupt an activity whether it isdisturbing the peace and/or quiet, interfering with communication, ordisrupting sleep.

Why and When Does the Air Force Evaluate Noise?

The Air Force evaluates aircraft noise so they know how their flightoperations affect land uses, humans, animals, and structures. The resultsof noise analysis are primarily used by two programs: the Air InstallationCompatible Use Zone (AICUZ) program and the Environmental ImpactAnalysis Process (EIAP).

The AICUZ program applies specifically to the installation vicinity.Evaluations occur on a 2-year cycle or when a change in the airfield orairspace noise environment is anticipated as a result of new or revisedflight activity. With this program, noise levels from daily aircraft operationsare calculated over a 24-hour period and presented as day-night averagesound level or DNL (mathematically denoted as Ldn) in the form of noisecontours.

The noise contours are used in conjunction with land use guidelines toassist local, regional, state, and federal officials in protecting public health,safety, and welfare by promoting compatible development adjacent to the

installation. Adoption of AICUZ recommendations by local communitieshelps to protect the installation’s flying mission and future capabilities.

Noise evaluated during theEnvironmental Impact AnalysisProcess applies to installationsas well as military training rangesand airspace. A noise analysisoccurs when the Air Forceproposes a change in aircraftand/or operations. During theanalysis process, noise levels areused as one of the gauges tomeasure the significance of changing the type and/or numberof aircraft overflights. The results

help Air Force leaders inform thepublic of potential noise impactsand assists in the decision-making process for proposedoperational changes.

What does an assessment of military aircraft noise include?

When the Air Force assesses aircraft noise they must first characterize theexisting noise environment. This includes identifying the types of aircraftflying in the area, how often they fly, and at what altitude and airspeed. Theseparameters are used as input to computerized noise models that produce variousnoise metrics. The most common metrics are DNL, DNLmr (or Ldnmr), SELs(sound exposure levels), and Lmax (maximum noise levels).

DNL represents daily aircraft operations averaged over a 24-hour period witha 10-decibel penalty to flights occurring between 10 p.m. and 7 a.m. to account

for the added intrusiveness during these hours (note: in California, CNEL [orcommunity noise level] adds a 5-decibel penalty to flights occurring between7 p.m. and 10 p.m.).

DNLmr is similar to DNL but incorporates an additional penalty of up to 11decibels to account for the startling effect caused by aircraft flying at low-altitudes and high speeds.

SEL and Lmax are metrics used to describe the sound level of one aircraftoverflight; both are determined by aircraft power, altitude, and airspeed andits distance from the receiver.

Noise metrics are used to measure the potential effects of an Air Force actionon humans, wildlife and domestic animals, and noise sensitive areas such ascritical habitats, national wildlife refuges, parks, national forests, historicstructures, and others. Computerized, geographic information systems as wellas other data are used to identify these receptors and the existing and proposedareas of influence are delineated and examined for noise effects. Once theareas of influence are identified, noise effects are characterized based onexisting and proposed overflight changes and the resources potentially affected.

These resource areas are examined, changes are compared, and in turn, thesignificance of the proposed change is then determined. The specific metric(e.g., DNL, DNLmr, SEL) used for analysis is determined by the resourcebeing analyzed.

What resources are analyzed?

Noise is presented as an individual resource areanalysis; however, because noise affects many resin specific resource areas such as land use, culturesources, and environmental justice. When a noas part of the environmental impact analysis procehow the change in noise levels affects humans, ain the vicinity of the airfield and beneath militar

What is the focus of Air Force noise an

Air Force noise analyses evaluate both the cumeffects of noise on specific resources. The metrresource evaluated.

DNL is the most commonmetric used to evaluatenoise effects on humans.Its use was recommendedby the EnvironmentalProtection Agency in 1974.After social surveys andother scientific studies,DNL was adopted by theFederal InteragencyCommittee on Urban Noise(FICUN) in 1980 as themost appropriate metric forpredicting cumulative

human effects. DNL isused by all federal agencies(Department of Defense,Federal AviationAdministration,Department of Transportation, etc.) forpredicting humanannoyance and otherpotential noise effects tohumans.

DNL is the energy averageof all noise events thatoccur during a 24-hourperiod—it is not the soundlevel heard at any given time. It is more reliabllevels when analyzing noise effects because it ainto account the entire exposed population ratheThe percentage of the population annoyed is baseof noise annoyance; most commonly referred to(Schultz 1978). The curve was updated in 1994 only minor changes from the original curve.

 DNL rules of

Doubling toperations yields an inof approxim

In terms of cone operatiduring envihas the sam

daytime op

Noise sourless powerfdominant nhave little tototal DNL.

Low-altituflights havethat can addto 11 decib

Thresholdfor compatible 65land use planning

Rural Daytime 45Outdoors

Quiet Urban 40Daytime

Thresholdof hearing0 dBa

AFB boundary

Roads

Numeric labels includeDNL level

8/3/2019 Aircraft Noise - An Environmental Perspective

http://slidepdf.com/reader/full/aircraft-noise-an-environmental-perspective 2/2

Cumulative noise levels in military airspace are presented usingDNLmr, which is defined as an “onset-rate” adjusted monthlyDNL. DNLmr is used in a similar manner to DNL when assessingnoise impacts in military training areas.

Sound exposure levels (SELs) are a measure of the total physicalenergy of a single noise event, which takes into account bothintensity (loudness) and duration. SELs are used as an indicatorof activity interference for humans and for impacts to domesticanimals and wildlife. Lmax is also presented for comparisonpurposes and represents the peek noise level of a single event.

Some aircraft operations may result in structural vibrations and,in extreme cases, structural damage. Damage may be associatedwith sonic booms produced by supersonic operations or

overpressures and is denoted as CSEL or CDNL.

What tools are used to conduct the analysis?

The Department of Defense has various approved computerized modelsthat assist in analyzing aircraft noise impacts including NOISEMAP,MR_NMAP, BOOMAP, PCBOOM, and CORBOOM.

NOISEMAP is the primary tool for evaluating military aircraft noisein the vicinity of a military installation. NOISEMAP predicts noiseexposure based on aircraft flights and maintenance activities occurringduring an average busy day. NOISEMAP also generates reports thatprovide the analyst with the primary contributors to the overall DNLat any given location.

MR_NMAP, known as Military Operations Area (MOA) RangeNOISEMAP, calculates noise levels under special use airspace such asRestricted Areas (RAs), MOAs, Military Training Routes (MTRs), andRanges. This program produces noise level data in table format andcontours; the data are then used to analyze effects in EIAP documents.

 In conclusion . . .

Noise analysis is a very important part of the environmental impactanalysis process. The Air Force strives to present aircraft noiseinformation in a detailed, yet accessible manner for the public. Moreinformation about noise analysis and metrics can be found by visitingwww.a7zpintegratedplanning.org and reviewing the noiseappendix in EIAP documents (e.g., F-22 Initial Operational WingBeddown EIS, Appendix AO-2). For assis tance or any questions aboutnoise analysis, please contact:

HQ ACC/ A7ZP  Integrated Plannning Branch129 Andrews Street, Suite 102Langley AFB, VA 23665-2769

0

10

20

30

40

50

60

70

80

90

40 45 50 55 60 65 70 75 80 85 90

DNL (dB) 

-2.8 -1.4 0 1.4 2.8 4.2 5.6 7

Onset(Approaching)

Recess(Leaving)

SoundExposure

Level

Observer 

Maximum Sound Level120

100

80

60

40

20

0

Time, Seconds

1 Sec

 Aircraft Noi An Environmental Pe

The Air Force’s mission is to defend the Uniits interests through aerospace power. To fulForce pilots require continuous, realistic traidefensive flight maneuvers and weapons deliresulting from this training is of special conc

because it is not confined to a specific area aof affecting humans, animals, and structures The purpose of this brochure is to assist the gunderstanding basic information about how nto characterize the noise environment and suppo