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

4 Conclusions and Recommendations

The calculation results in Section 3 show that a reduction of the number of meteo-classes in the weather statistics which is based directly on the parameter D/R used in the IMAGINE work will lead to a significant overestimation of the yearly average of L_den.

A more neutral estimate is obtained in the investigated propagation cases by Proposal 2 which is recommended.

If a more conservative estimate is desirable, it can be recommended to use Proposal 3 where L_den shows only slightly higher values than Proposal 2 for flat terrain, but where the calculated values in screen cases are overestimated by approx. 1 dB. Still, from an acoustical point of view a neutral simplification is provided by Proposal 2.

Due to the financial limitations in the present project the effects of reducing the number of meteo-classes have only been investigated for a limited number of terrain cases. However, it is expected that the magnitude of deviations between calculations using the nine meteo-classes and the recommended proposal will be acceptable in other terrain cases.

The statistics reduced to four meteo-classes shall only be applied when the calculation time plays an important role such as in the case of strategic noise mapping. In other cases it is recommended to use the nine meteo-classes to obtain the best accuracy.

For a city environment where L_den is dominated by shorter distances to the noise vehicles and by a considerable number of reflections is recommended to use only one meteo-class. This is also in accordance with the recommendation of IMAGINE (mentioned at the final conference in Budapest, October 2006). Due to shorter distances the weather will be of less importance in many cases, and in cases where weather effects are expected to be significant it is doubtful that weather conditions defined by the weather statistics are of relevance to the local weather conditions in the city streets. It is recommended to use meteo-class 13 for city environments corresponding to a homogeneous atmosphere.