Supplemental Noise Metrics

What are supplemental noise metrics?

To analyze the impacts of aviation noise, the Federal Aviation Administration (FAA) uses the Day-Night Average Sound Level (DNL) as the primary metric for quantifying individuals’ cumulative exposure to aircraft noise. Noise impact analysis around airports can be supplemented by computing other metrics, referred to as “supplemental”, to provide more information about noise from aircraft operations. These type of metrics used to measure noise depends on the community and their activity.

Click here for more information on FAA policies and procedures regarding environmental analysis supplemental noise analysis.

Supplemental metrics include:

These metrics are computed in existing aircraft noise computer programs.

Another metric used in supplemental noise analysis but not computed in existing aircraft noise computer programs is

• Number-of-events Above a Specified Sound Level (NA)

Which supplemental noise metrics are commonly used?

  • The most appropriate metric for a study varies. It depends on the purpose of the analysis, the audience, and several other factors.
  • The most commonly used additional metric is the NA. This is because it asks the question, "How often will I hear airplanes and how loud will they be?"
  • The TA and NA are often used to supplement the DNL metric. This is because the TA and NA break the DNL metric into its component parts. These metrics measure the number of times noise above a certain level is produced in a given time period (NA) and the total time you hear such noise in a given time period (TA).

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