2.6  How reliable is environmental noise modelling?

The reliability of environmental noise modelling is a very important question, but one that is all too often addressed by potentially misleading statements about 'accuracy' in the sense of the closeness between measured and predicted values.

A noise model represents an estimate of a 'snapshot' in time. As will be discussed further in the following section, environmental noise fields tend to be inherently variable in both time and space. This variability introduces a difficulty in defining the accuracy of a model, as it is a function of the relationship between a constant predicted value and a potentially widely varying noise level that could be measured in practice.

The value of a model cannot be measured by accuracy per se, but rather on a judgement of its reliability as a tool in decision making, and this judgement should be made according to the specific application and situation under consideration. Providing that modelling studies are used with an awareness of the relative benefits and limitations of predictions when compared to other possible bases upon which a decision could be made, such studies can provide a reliable basis for decision making purposes. In other words, a reliable model is one that is fit for purpose.

It is the purpose of this guide to assist all parties involved in these types of studies to identify those situations where predictions can offer a reliable decision making tool, and subsequently design case specific approaches to modelling that is focussed on producing reliable information that is fit for the purpose of the decision making exercise. The requirement of fit for purpose information establishes an onus on practitioners to deliver the outputs of predictive studies with accompanying contextual information that enables decision makers to understand how such information can be used.

2.7  Are there standardised methods of modelling?

At present, there is no ratified methodology within the UK that describes exactly when or how environmental noise modelling should be used. Approaches to how environmental noise models are developed and presented is largely dependent on individual practitioner judgement and experience. The purpose of this document is to promote a greater level of transparency and consistency to this process.