|
Forest Excess Attenuation |
Previous Next |
|
Af, the excess attenuation due to forest is obtained by the following:
Af = 0.01 r f (1/3) where r = distance through the forest in (m), and f = frequency in (Hz)
PEN Implementation
The forest attenuation calculation incorporates a sophisticated method to calculate the total sonic gradient. This method incorporates the vertical wind profile for various types of surfaces. The sonic gradient also changes with height above the ground. As a consequence, depending on the type of surface, the sonic gradient will vary over the DTM and vary with height of the noise ray. These issues have been addressed in the PEN model and a most likely curved path is calculated by iteration. Up to 250 possible iterations of the curved path are calculated for each sound ray.
Once the most likely curved path has been calculated the method determines if to intercepts any tree zones.
If the curved noise path travels in the lower 75% of the tree zone then the full excess attenuation is applied for the distance traveled in the tree zone.
If the curved noise path travels in the upper 25% of the tree zone then:
|