BS5228 seems to use hemispherical spreading whilst ISO 9613 seems to use spherical spreading. Does this mean that SiteNoise is not appropriate for Wind Farms, which have a source very high above the ground?
I think this question arises from a misunderstanding of ISO 9613. It is true that the constant in the initial sound power to sound level conversion is 3 dB different in the two methods (ie equivalent to spherical spreading in ISO 9613), but if you look at the ground attenuation formulae in ISO 9613 (which are very obscure, admittedly), you will see that for hard ground, the 3 dB is added back when you do the hard ground calculation, making the two methods identical. If the ground is porous (i.e. soft) then a further amount of correction is applied, which still takes the ground reflection into account. So in fact both methods account for reflection from the ground plane. They just do it differently. Basically, there is always some degree of ground reflection.
