Division Attenuation through absorption
United Kingdom
The reflections on vertical obstacles are dealt with by means of image sources. Reflections on building façades and noise barriers are thus treated in this way.
An obstacle is considered to be vertical if its slope in relation to the vertical is less than 15°.
When dealing with reflections on objects which slope in relation to the vertical is more or equal to 15° the object is not considered.
The obstacles where at least one dimension is less than 0,5 m shall be ignored in the reflection calculation, except for special configurationsf1.
Note that reflections on the ground are not dealt with here. They are taken into account in the calculations of attenuation due to the boundary (ground, diffraction).
If LWS is the power level of the source S and αr the absorption coefficient of the surface of the obstacle as defined by the EN 1793-1:2013, then the power level of the image source S′ is equal to:
| LWS′ = LWS + 10 · lg(1 – αr ) = LWS + Arefl | (2.5.35) |
where 0 ≤ αr < 1
The propagation attenuations described above are then applied to this path (image source, receiver), as for a direct path.
Figure 2.5.g
Specular reflection on an obstacle dealt with by the image source method (S: source, S′: image source, R: receiver)
Annotations
Footnotes
- f1
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A network of small obstacles in a plane and at regular intervals constitutes one example of a special configuration.