Noise Contours Explained
Airport noise is, understandably, a significant issue for some of our neighbouring communities. Achieving the most appropriate balance between the needs of a growing airport that serves as a major transport hub for millions of business and leisure travellers, and the rights and requirements of our nearest residential neighbours provides an ongoing challenge for Dublin Airport as it does for all airports of its size.
Noise is subjective and personal to each individual. Aircraft generate noise both on the ground and in the air. The amount of noise generated depends on the type of aircraft and how it is operated. Aircraft noise is measured in decibels (dB). Aircraft entering the market today are 20dB quieter than aircraft of 40 years ago, and this trend for quieter aircraft is expected to continue into the future.
Noise is measured on a logarithmic scale with the decibel (dB) as the unit of measure. Measurements of noise are usually weighted to reflect the sensitivity of the human ear. This is referred to as “A-weighting” and environmental noise is usually measured in dB(A) units. The noise level of normal daytime urban-based activities typically varies between 40dB(A) and 85dB(A). On this scale, a change in noise level of 10dB(A) is perceived to be a doubling or halving in loudness. For example, most humans perceive a noise event of 85dB(A) to be about twice as loud as an event of 75dB(A).
Below is a decibel chart which shows the typical decibel levels of different noise sources.
The standard method for assessing noise impacts from airborne aircraft involves the production of noise contours which illustrate the spread of noise around the airport. The contours join together locations that are exposed to the same levels of noise. There are a number of different parameters than can be used to describe the effects of noise, many of which determine an ‘average’ level of noise across a given period.
The most commonly used unit to rate airborne aircraft noise is the LAeq unit, known as the equivalent continuous sound level, which describes the average noise received at a point over a given time.
A common pair of parameters used for this purpose are the daytime level (LAeq,16hour) and the night-time level (LAeq,8hour) for an average summer day period. These illustrate the average level, as on a daily basis there will be some variation. The summer period is used as it is usually the busiest period for an airport. The contours can be prepared at a range of values which have different levels of significance, based on aircraft movements, types and associated noise emission levels for the given period. This approach is in line with international best practice and is used at a number of airports worldwide. Average contours for the annual period are also commonly used for strategic noise mapping and are the standard for reporting under the Environmental Noise Directive. Dublin Airport produces these contours every 5 years and submits them for inclusion in the Dublin Agglomeration Noise Action Plan.
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