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Noise mapping by use of Nord2000 – Reduction of number of meteo-classes from nine to four
3 Results
New weather statistics have been created where the number of weather classes is reduced to four. This has been done for each of the three proposals for combining the original meteo-classes described in Section 2.
For the three proposals the effect of reducing the number of meteo-classes for 20 propagation cases has been determined as described in Section 2. The results are shown in Table 4.
Table 4: Calculated changes in Lden when reducing the number of meteo-classes from nine to four according to Proposal 1-3.
| Terrain |
Receiver position |
Distance (m) |
Lden (dB) |
Changes in Lden (dB) |
| Proposal 1 |
Proposal 2 |
Proposal 3 |
| Flat |
East |
25 |
64.4 |
0.9 |
0.3 |
0.4 |
| Flat |
West |
25 |
63.8 |
0.9 |
0.3 |
0.4 |
| Flat |
East |
50 |
60.8 |
1.1 |
0.4 |
0.5 |
| Flat |
West |
50 |
59.9 |
1.2 |
0.4 |
0.5 |
| Flat |
East |
100 |
58.4 |
1.0 |
0.3 |
0.4 |
| Flat |
West |
100 |
57.3 |
1.1 |
0.3 |
0.4 |
| Flat |
East |
200 |
55.6 |
0.4 |
0.1 |
0.2 |
| Flat |
West |
200 |
54.4 |
0.4 |
0.1 |
0.2 |
| Flat |
East |
500 |
50.0 |
0.0 |
0.0 |
0.0 |
| Flat |
West |
500 |
48.7 |
0.0 |
0.0 |
0.0 |
| Screen |
East |
25 |
60.3 |
2.2 |
0.8 |
0.9 |
| Screen |
West |
25 |
59.5 |
2.4 |
0.8 |
1.0 |
| Screen |
East |
50 |
57.2 |
1.9 |
0.6 |
0.9 |
| Screen |
West |
50 |
56.4 |
2.0 |
0.6 |
0.9 |
| Screen |
East |
100 |
52.8 |
1.4 |
0.2 |
0.8 |
| Screen |
West |
100 |
52.1 |
1.5 |
0.2 |
0.8 |
| Screen |
East |
200 |
49.0 |
1.4 |
0.0 |
0.8 |
| Screen |
West |
200 |
48.1 |
1.4 |
-0.1 |
0.8 |
| Screen |
East |
500 |
43.7 |
1.4 |
-0.1 |
0.9 |
| Screen |
West |
500 |
42.7 |
1.4 |
-0.4 |
0.9 |
| Average deviation |
1.2 |
0.2 |
0.6 |
Table 4 shows that Proposal 1 where the combination of the meteo-classes is solely based on the parameter D/R as used by IMAGINE leads to a general overestimation of Lden as already suggested in Section 2. The average deviation of the calculated cases is 1.2 dB with a maximum deviation of 1.2 dB for flat terrain and 2.4 dB for screens.
Moving meteo-class 19 from propagation class “M4” to “M³” in Proposal 2 clearly improves the agreement between the calculation where all nine classes were used and the four-class approach. The average deviation of the calculated cases is 0.2 dB with a maximum deviation of 0.4 dB for flat terrain and 0.8 dB for screens.
The use of meteo-class 19 in Proposal 3 to represent propagation class “M³” instead of meteo-class 18 in Proposal 2 will only increase the Lden slighly for flat terrain. However, for screens Lden will be overestimated by approx. 1 dB.
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Version 1.0 March 2007, © Danish Environmental Protection Agency
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