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Noise 101

How is aircraft noise described, quantified, and managed?

Aircraft Noise Metrics

  • What is noise?
    • Noise is unwanted sound; what is music to music to one may be noise to another
    • By its very nature noise is subjective
    • Noise cannot be measured, only sound can be measured
  • Sound pressure ranges are very large, therefore expressed on a logarithmic scale
  • Logarithmic scale compresses the wide range in sound pressures to a more useable range
  • Standard unit of measurement is the decibel (dB), which is the basis for aircraft noise analysis

Sound Environs

The following is a graph of Sounds Environs:

Common Sounds

The chart below shows noise levels for common sounds found indoors and outdoors:

Propagation of Noise

  • Sound levels decrease primarily as a function of:
    • Distance from source
    • Atmospheric absorption
    • Ground attenuation
  • Overall, atmospheric conditions play a significant role in affecting the sound levels on a daily basis and how these sounds are perceived by the public.
  • The atmosphere can absorb sound depending on the temperature of the air and humidity levels
    • Less sound will be absorbed by the atmosphere on days with high humidity and high temperatures
    • Temperature inversions (or cloud cover) can cause the sound to reflect back to the ground
  • Ground absorption is important to the study of noise from airfield operations
    • Closer the source of the noise is to the ground, the more the sound will be  attenuated by the ground
    • Soft surfaces, such as vegetation, absorb more sound than hard surfaces like water

Quantifying Noise Exposure

  • Noise exposure can be quantified using measurements or modeling
  • Measuring sound levels will accurately tell us:
    • The sound levels at a specific location for the time period measurements were made
    • Historical record of the sound levels at a specific location
    • Historical trends; but measurements do not predict future noise levels
  • Modeling sound exposure accurately tells us the sound levels
    • Over broad geographic areas as well as at specific locations for a specific time period
    • Modeling can produce a historical record
    • Modeling can be predictive by showing expected trend

Managing Aircraft Noise

  • Management of aircraft noise falls primarily into two categories:
    • Aircraft Operational procedures—Abatement
    • Land use measures—Mitigation
  • Extent of available Noise Abatement programs varies based on the extent and complexity of the noise concerns at the airport
  • Programs should be safe, cost effective, and capable of being implemented to be successful
  • Examples include:
    • Preferential runway use program
    • Modify approach and departure procedures
    • Limit operations, such as touch-and-go operations
    • Designated traffic patterns
  • Noise mitigation refers to measures that address existing and future non-compatible land uses in the vicinity of airports
  • Examples of noise mitigation include:
    • Airport Land Use Compatibility Plan
    • Sound insulation
    • Zoning/building codes

Regulatory Framework

  • Federal law sets aircraft noise standards, prescribes operating rules, establishes the compatibility planning process, and impedes the airport proprietor from implementing operational restrictions
  • State law sets forth compatibility planning guidelines and noise standards but exempts aircraft in flight
  • Local noise ordinances set noise standards and provide for compatible land use planning but exempt aircraft in flight

Federal Law Preempts State and Local Regulations Pursuant to Aircraft in Flight