How aviation noise is measured in the UK
Unlike most other forms of pollution, noise pollution depends not just on the physical aspects of the sound itself, but more importantly the human reaction to it. There are no European or national noise limits which have to be adhered to: instead, the issue is the effect on people’s health and quality of life. This makes measuring noise pollution a complex process. This page describes how aviation noise is measured – and how it is determined whether this is noise pollution.
How loudness is measured
The loudness of sounds is generally measured in terms of decibels (dB). Near-total silence is 0dB, normal conversation takes place at around 60dB, a heavy lorry passing 15 metres away is likely to be around 80dB, and a jet aircraft taking off is generally around 100dB at a distance of 300 metres.
Because of the way the decibel scale works, a doubling of noise energy results in an increase of 3dB. A change of 3dB has been defined as the minimum that is perceptible under normal conditions. By contrast, a change of 10dB corresponds to roughly a doubling or halving of loudness.
The human ear is less sensitive to sounds at low and high frequencies, and so, there is an adjustment, known as ‘A-weighting’, which gives more weight to the noises (frequencies) that people are most sensitive to. The A-weighting adjusts decibel values so that they best reflect how loud a noise is to a person. Noise levels that are A-weighted are indicated by the ‘A’ in dBA and LAeq.
Other types of noise
These noise measures don’t only apply to aviation noise. They also apply to noise from roads and railways, noisy venues – such as pubs and motor racing circuits – and even some factories.
Within European cities, it is estimated that almost 70 million people suffer from road noise exposure above 55dB Lden. In contrast, the number for aircraft noise is estimated at 2.5 million people. However, there are important differences: where road noise tends to be constant, aviation noise tends to have higher peaks with each take-off and landing. Also, in areas closest to airports, the noise levels are often significantly higher than road noise.
Helicopter noise is far more complex to measure and assess than fixed-wing aircraft noise. This is mainly because helicopters often don’t have to follow predefined routes, like fixed wing aircraft, and because helicopters may hover over a specific area for a while making the impact of the noise last for longer. Also, variations in the speed of the rotor blades means that the way noise travels also varies, and results in an asymmetric noise distribution, i.e. different noise levels from one side of a helicopter to the other.