Uncertainties in Environmental Noise Modeling

With sound level meters the measurement uncertainty is fixed and transparent, depending on the class of the instrument. The counterpart of the measurement, the noise simulation, has many more uncertainties. The uncertainties stem from the calculation standard used, the application of the model’s theoretical basis in a computer program and the construction of the data model. The uncertainty of the simulated results is the sum of the uncertainties of the applied standard, the computer program and the physical representation of the reality in a computer model. The end user only has influence upon the creation of the data model and most likely is not aware of the other uncertainties. The assessment of the sources sound power is also an uncertainty but will not be discussed in this paper. This paper is concentrating on the use of popular standards and their built in systematic errors and shortcuts in the evaluation of propagation parameters. Special focus is given to the evaluation of the ground effect. Discussed standards include CoRTN, CoRRN, CONCAWE, ISO9613, GPM (Nordic) and Nord 2000. Testing routines and procedures both listed in the standard and external are to be shown and comments made. Other sources of uncertainty are the transition from area and line sources to the evaluated point sources and the acceleration techniques in the modeling software. In the near future one can hope that the shortcomings in today’s standards are avoided with the next generation of noise models conceived at the moment in Europe.