Noise map
A noise map is a graphic representation of the sound level distribution existing in a given region, for a defined period.
Directive 2002/49/EC
Although some previous approaches had been made, the main international agreement, definitions, and basis for noise mapping were born in relation to the Environmental Noise Directive of the European Parliament and Council (Directive 2002/49/EC of 25 June 2002, commonly referred to as 'the END'), where we can find the following definitions:
' environmental noise’ shall mean unwanted or harmful outdoor sound created by human activities, including noise emitted by means of transport, road traffic, rail traffic, air traffic, and from sites of industrial activity.
' noise indicator’ shall mean a physical scale for the description of environmental noise, which has a relationship with a harmful effect;
-' strategic noise map’ shall mean a map designed for the global assessment of noise exposure in a given area due to different noise sources or for overall predictions for such an area;
' action plans’ shall mean plans designed to manage noise issues and effects, including noise reduction if necessary;
' acoustical planning’ shall mean controlling future noise by planned measures, such as land-use planning, systems engineering for traffic, traffic planning, abatement by soundinsulation measures and noise control of sources;
EU Member States are required to produce strategic noise maps in their main cities, near the main transport infrastructures and near industrial sites. The main goals of the END are to make a diagnosis of noise pollution in Europe that can lead to action plans, and a noise management that can be implemented in terms of action plans and acoustical planning. The term 'strategic' is very important in this definition, because the management of environmental noise must be made for the long-term in a full area. Using a simile, we should not worry about the weather, but we must care about the global warming.
Production
The main noise indicators for noise mapping are Lday, Levening, Lnight and Lden (day-evening-night). These are long-term averaged sound levels, determined over all the correspondent periods of a year. All of these indicators are defined in terms of A-weighted decibels (dBA, dB(A)). According to the END, the acoustic indicators can be determined by computation or measurement methods. But computation methods are widely preferred, because of the large amount of yearly averaged locations required. Using either approach, a grid of receivers must be defined in order to measure or calculate noise levels. When results are obtained, using GIS tools, spatial interpolation must be applied in order to give a continuous graphical representation of sound levels. Five dBA ranges are used for this contour (isoline) representation. The maps may be useful for planning stages, or for prior evaluation of action plans, determination of most polluted areas. A strategic noise map, furthermore, must make an evaluation of the amount of people exposed within the five dBA ranges. Facade sound levels must be calculated, or estimated from the previous map.
Simulation tools
There are several models for making noise maps. Some of them use empirical models (for instance, INM for airports noise mapping), but most of the models are based in the physics of propagation of sound outdoors (defined in ISO 9613). The use of these software packages is quite easy, and the accuracy of results is very high depending on the quality of input data to the models. Measurements are used very often for the validation of results.
For train and road traffic noise, the description of the sources is usually made in terms of easy to know parameters, such as speed, number of vehicles etc. The main challenge for the acoustic consultant is the creation of good digital terrain model (DTM).
For industrial noise map production, the most important thing is the description of noise sources: sound power levels, directivity, working periods. Although some databases can be found, in many cases it is necessary to make measurements (ISO 3740) for describing the source. When these data are known, it will be necessary to simulate each of sources using a combination of point, line or surface noise source. The creation of good acoustic models can be quite complicated, and only experienced consultants can front this difficult tasks.
Some of the software packages more used for noise mapping are: LimA, CadnA, IMMI, Predictor, Olive Tree Lab Terrain[1] and SoundPlan. These programs have been adapted to fulfil the strategic noise mapping requirements of the END.
Simulation tools are very useful specially at planning stages, where measurements are not possible. The consultant can evaluate the effectiveness of action plans, in order to take decisions.
References
Cnossos-EU: common noise assessment methods for EU
Directive 2002/49/EC of the European Parliament and of the council, of 25 June 2002 relating to the assessment and management of environmental noise
ISO 1996.Acoustics—Description, measurement and assessment of environmental noise
ISO 9613.Acoustics—Attenuation of sound during propagation outdoors
European Commission – Noise policy
Senat Department of Urban Environment - Berlin
Centro de Acústica y evaluación no destructiva (UPM-CSIC)
Urban Environment Information Gateway - Noise maps in Prague
Official websites of the city of Prague
Noise and Traffic information - Noise maps - Vienna
UK Department for Environment, Food & Rural Affairs - Noise Mapping England website
Integrated noise model (airports noise)