Methods of portraying aircraft noise

Explanation of the different methods used to describe noise impacts around an airport

Noise metrics

Various noise metrics or noise indicators are in use in the UK to portray the impacts of aircraft noise around airports.  The most common ones are described below:

Leq - this is the 'equivalent continuous sound level', i.e. the average sound level calculated over a defined measurement period.  In the UK, Leq noise contours are produced for the average summer day, where 'summer' is the 92-day period from 16 June to 15 September, and 'day' is the 16-hour period 0700-2300 (local time). 

Leq contours are normally plotted from 57 to 72 dBA at 3 dB intervals. The daytime 16-hour 57 dBA Leq contour corresponds to the onset of significant community annoyance based on large scale studies in the UK.

Leq contours  © Crown copyright

SEL - 'sound exposure level' noise footprints are sometimes plotted to depict the noise from an individual aircraft movement, such as a departure or landing. SEL is effectively a 1-second Leq, i.e. the sound energy from a single event is normalised to a reference time period of one second. The 90 dBA SEL corresponds to the threshold of sleep disturbance based on large scale studies in the UK.

Departure SEL footprints

N70 - N70 is a metric which originated from Australia and it describes the number of noise events (N) exceeding an outdoor maximum noise level (Lmax) of 70 dBA. The 70 dBA outdoor level was chosen because it corresponds to the Australian standard for the onset of indoor speech interference of 60 dBA (10 dB attenuation by the building fabric with open windows is allowed for).

N70 contours  © plc


European Directive noise metrics for noise mapping

Under EU Directive 2002/49/EC, noise maps were generated for major airports in 2007 (for the year 2006) using the following noise metrics:

Lden - the annual average 24-hour Leq, with weightings of 5 dB for evening (1900-2300) and 10 dB for night-time (2300-0700);

Lday - the annual average 12-hour Leq for daytime (0700-1900);

Levening - the annual average 4-hour Leq for the evening period (1900-2300);

Lnight - the annual average 8-hour Leq for night-time (2300-0700).

The next round of noise mapping will be carried out for the year 2011.

Lden contours © Crown copyright

Airport operations diagrams

‘Airport operations diagrams’, which are based on a concept originating from Australia, are sometimes used to supplement conventional noise contours.  They are a useful non-technical means of describing the potential noise impacts around an airport without referring to actual noise levels.

The swathes followed by aircraft on different routes can be shown on the diagram, along with useful statistics such as the frequency and range of daily aircraft movements.

Airport operations diagram

Find out more about the special features of the ANCON modelling process.

Go back to the noise contours page.