Air traffic noise can be determined in two ways: either it is calculated or it is measured. A measurement can only register the actual status at a point. With a calculation, however, it is possible to represent noise burdens over an area in the future. 

How is air traffic noise calculated?
With today’s noise calculation programs it is possible to model complex situations and to use them for the assessment of the noise burden at the incidence point. Architectural acoustic measures in buildings, such as noise insulation between rooms, can be calculated if the necessary data such as building material characteristic values and construction details are known. If we want to calculate air traffic noise we need information on the departing and arriving aircraft: number, size, weight and technical equipment of the aircraft as well as the type of operation, i.e. flight altitude and flight routes. These data are fed into mathematical models, the results of which are referred to as isophones. These are graphical representations of the noise burden in the form of lines.

Which methods are used for calculation?

Air traffic noise can be calculated using various recognised methods. In Germany the “Instructions for the calculation of air traffic noise” (AzB) apply subject to the air traffic noise law. The AzB consists of two components, a calculation regulation and the data for noise development in certain aircraft types. The database of the AzB, the so-called data registration system (DRS), contains data on the airport (e.g. number and length of the runways, geographical location), the arrival and departure routes (e.g. designation, description of the flight paths and corridors), as well as the flight movements (number per aircraft group on a certain route, separated according to day and night) and is drawn up according to the “Instructions for data registration” (AzD).

FLULA 2 is a simulation method developed by the Swiss Federal Laboratories for Materials Science and Technology (EMPA) to calculate air traffic noise which was used for example within the framework of the RDF assessment Air Traffic Noise Monitoring. With the aid of this method it is possible for example to calculate equivalent continuous sound levels Leq(3), Leq (4). Alongside the AzB and FLULA, other methods are used for calculation, for example in the USA a different method, the Integrated Noise Model (INM), is the standard used. The methods are only comparable with each other to a limited extent as they proceed from different assumptions and use different computing methods.

How reliable are the results of the calculation?

It is important to realise that calculations are model assumptions which provide a generally useful reflection of the reality but can never fully reflect the actual situation at a certain time at a certain location. 

Which is better: calculation or measurement?
This question cannot be answered clearly in the affirmative either way. It ultimately depends on what the results are to be used for. Depending on the task and aims, a decision must be made for one or the other method. For forecasts, only a calculation can be used. For determination of the actual situation, measurements are preferable. Measurement or calculation accurate to the decimal place is not possible. There are uncertainties with both methods.