In this section, you will learn about noise, including:
- The basics of sound
- Sound perception and hearing
In addition, you will learn about
- Efforts that have been undertaken to reduce noise
- Regulations from the Federal Aviation Administration aimed at reducing noise
- Regulatory guidance for planning for noise compatible land uses on and around airports
Finally, this section will discuss models and metrics used to measure noise and the impact of weather on aviation operations.
First and foremost, it is important to understand what is noise. This is discussed inthe following section.
What is Noise?
Noise can be defined as any unwanted sound. What sounds annoy you may or may not annoy someone else. In addition, what sounds annoy you can vary, depending on the situation.
Here are some things that affect your level of annoyance:
- Time of Day - For example, you may be more upset by noise heard at night while you are trying to sleep or relax, than from the same noise heard during a busy day at work. Noise at night may also be more noticeable because the background noise level is lower than during the daytime.
- Length of Time - The longer you are exposed to a noise, the more it may annoy you.
- Predictability - If you cannot predict when the noise will occur, it may annoy you.
- Control - If you have little control over the noise, it may annoy you.
- Emotional Variables - Emotional noise variables are those that cause differences in your perception of a noise. It depends on your experiences, values, beliefs, and mood. If you believe that a noise is unnecessary or unimportant, you may be more annoyed by the noise. For example, if you were awakened by noise from an airplane that you believed was transporting tourists, you could be irritated. On the other hand, if you knew the airplane was transporting goods such as food, medicine, mail, and other perishable necessities, you may be more willing to tolerate the disturbance.
- Physical Surroundings - Surroundings such as snow, grass, trees, and other vegetation can help alleviate noise by reducing the sound through absorption or deflection of sound waves. However, during the summer months, open windows and more time spent outside may expose you to more noise.
Many variables influence people's perception of noise. However, since the level of annoyance changes from person to person, it is difficult to determine what is too noisy or annoying for an entire community. This extremely complex human response to noise makes noise impact assessment a challenging task.
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).