- Understanding aviation noise
- Noise concepts
- Suppose we put a sonometer properly to measure the airport noise for one hour and there is only one aircraft flying during this period in this area, after one hour. In that case, our sonometer will reflect LAmax = 80,3dBA, LAeq_event 71,5dBA, LAeq_1h = 57,5dBA.
- If there are eight identical aircrafts overflying along this period, after one hour our sonometer will reflect LAmax = 80,3dBA, LAeq_event 71,5dBA, LAeq_1h = 65,5dBA.
- If there are seven identical aircrafts and one different aircraft overflying along this period, after one hour our sonometer will reflect LAmax = 80,3dBA, LAeq_event1-7 = 71,5dBA, LAeq_event8= 70dBA, LAeq_1h = 65,4dBA.
- If there are 40 identical aircrafts overflying along this period, after one hour our sonometer will reflect LAmax = 80,3dBA, LAeq_event1-40 = 71,5dBA, LAeq_1h = 71,5 dBA.
As seen, this indicator reflects the number of events and the amount of energy of each event.
So far, we have concerned ourselves with the illustration of noise exposure at specific locations acknowledging the role of single events and the totality of exposure over a given time as influential in the individual perception of, and response to, noise. Another key aspect of noise management, however, is the implication of changes at multiple locations as this often associated with procedural fairness and equity. In order to capture the spatial implications of airport operations and thereby inform management interventions such as those associated with land-use planning, airports and regulators commonly use contour maps to summarise the spatial distribution of noise. Indeed, the EU Environmental Noise Directive places a requirement on all airports with more than 50,000 ATMs (air traffic movements) per annum to produce long-term aggregate noise exposure maps (based on Leq and its derivatives – see noise mapping) to highlight the geographical extent of noise exposure around Europe’s largest airports. Aircraft noise contour maps can be used to calculate the total areas, residential populations affected, numbers of schools and hospitals, or other potentially noise sensitive locations, geographically located within defined aircraft noise contour bands.
Important to remember
LAmax – the maximum sound level reached during a measurement period (normally 0.125 seconds for aircraft measurements), expressed in dB(A). However, it does not reflect the number of events and it does not reflect the amount of energy of each event.
Leq_event is the sound pressure level that would be produced by a constant noise level with the same amount of sound energy as the varying noise of the event during the event’s duration. This indicator can have different time reference periods (and sub-index): one second -LAeq_1sec, one hour -LAeq_1h, 24 hours -LAeq_24, a year -LAeq_day, LAeq_evening,LAeq_night, etc. It is the most important indicator for airport noise and environmental noise, which reflects the number of events and each event's energy.
SEL is an important indicator for aircraft noise comparisons but not for the general assessment of airport noise. It is helpful to compare aircraft events. This indicator reflects the total sound energy produced during an event but concentrated in one second.
It is important for the public to know the main indicators and the differences between them in order to compare airports and noise interventions correctly. It is essential to use appropriate indicators for the intended purpose. For example, if one airport is trying to assess the effectiveness of an intervention related to optimised climbing, Lmax and SEL are the best indicators to use. On the other hand, using long-time average LAeq to represent aircraft noise exposure at night can be particularly problematical for members of the public, who, if they happen to be disturbed while asleep, are much more likely to understand the disturbance to be directly attributed to specific events occurring at some stage during the night-time period (which could be represented by LAmax) than by a numerically much lower LAeq average.