Working Report No. 18 2007 – Noise mapping by use of Nord2000 – Reduction of number of meteo-classes from nine to four

Noise mapping by use of Nord2000 – Reduction of number of meteo-classes from nine to four

Summary and conclusions

In a joint Nordic work for calculation of noise from road traffic it was proposed that calculation of the yearly average of L_den and L_night should be based on 25 meteorological classes. A format was defined for the probability of occurrence of each meteo-class together with the average air temperature and relative humidity in the meteo-class for the day, evening and night period, respectively. The method has been accepted by the Danish Environmental Protection Agency, and the necessary statistics have been provided. The statistics included nine significant meteo-classes while the other classes contained no significant occurrences.

For strategic noise mapping the use of nine meteo-classes has subsequently been found too calculation time consuming. As the calculation time is proportional to the number of meteo-classes, it has been found necessary to reduce the number of classes.

As the result of the present work, a reduction to four meteo-classes is recommended for strategic noise mapping or other cases where the calculation time plays an important role. In cases where the calculation time issue is less important, it is recommended to use the original statistics with nine significant meteo-classes.

For a city environment it is recommended to use only one meteo-class (ignoring weather effects). Due to shorter distances and many reflections, the weather will be of less importance in many cases, and in cases where weather effects are significant, it is doubtful that weather conditions defined by the statistics are of relevance to the local conditions in the city streets.