NoiseMap 5.2.9 has now been given a full release.
(versions 5.2.7 and 5.2.8 were not released publicly)
ISO9613-2 Barrier Calculation
The headline feature in this release is a new ISO9613-2 barrier calculation option. This option is part of the SiteNoise Calculation module, which is based on BS5228 with enhancements.
This adds to the existing barrier calculation options in the SiteNoise module, namely
- BS5228 simple barrier calculations,
- BS5228 octave band spectrum barrier calculations,
- CRTN barrier calculations.
The ISO calculation requires octave band noise source data, as the attenuation is evaluated for each octave. The ISO procedure has a ‘meteorological correction’ which has the effect of reducing the path difference used to calculate the barrier attenuation. This correction is used to take into account the scattering of sound into the barrier’s shadow zone, caused by atmospheric turbulence under downwind propagation. This means that the barrier attenuation will be less than calculated by some other procedures.
It should also be noted that the NoiseMap implementation does not include the effect of diffraction around the vertical edges of barriers. The procedures described in the ISO provide for propagation over the top edges of multiple barriers one behind the other, but do not describe how diffraction from the vertical edges of multiple barriers should be assessed. This is an issue that other authors have commented on and various work-arounds have been suggested.
Although in particular circumstances (with a source and receiver just grazing the vertical edge, and with no other significant sources or barriers) this may lead to under-prediction, in general this is not considered to be a material issue.
It may also be noted that it is unclear as to how the ISO expects ground correction to be assessed in the presence of a barrier. This is again the subject of debate amongst authors. NoiseMap will assume hemispherical radiation (i.e. the presence of a ground reflection) and will correct this value either for the soft ground effect, or the barrier effect, but not both, using whichever gives the lower noise level.
NoiseMap Ltd has discussed these issues with a number of experts and considers that this is a reasonable implementation of the method.
NoiseMap is currently being used on several large, demanding projects with multiple remote users accessing the system over the internet. Under intensive use, this puts a heavy load on both client and server machines. We have made some internal changes to improve the efficiency of the process and reduce the demands on the server and internet.
A new release of the User Manuals is now pending.