Qualitative consideration of roughness lines survey

[surftrial]

Dear WAsP developers and users,

as far as I know WAsP can handle(or creates) up to 10 roughness changes in one sector.
Based on map data or digital orthophoto I create (CLC06 data)and adjust roughness lines.
With the help of high resoluted images I can align the roughness lines quite precisely and I can capture landscape elements which has not been recognized in CLC06 data before, tiny parts of settlements, Forrest clearing ...

Is it worth it to chart roughness lines that accurately, with regard of yield calculation?
Does WAsP take that slight differences due to roughness distribution significantly into account?
Exist a kind of map scale for working with WAsP, which advises for the aspect of roughness that a kind of map resolution (changing within a distance of x m is not considered?)

Mange tak, thanks!
surftrial

[Morten]

The WAsP helpfile has a section called 'Accuracy and detail of the map' which contains this explanation:


"The roughness classification should preferably extend to max(100×h, 10 km) from any site likely to be investigated; where h is the height of interest above the ground. If extensive water surfaces occur in the area, it may even be extended to 15 km (150 h) or more. Topographical maps on scales of 1:25,000 or 1:50,000 are well suited for roughness length classification and preparation of the roughness map.

The roughness-change line descriptions close to the prospected site(s) should be as detailed and accurate as possible. Conversely, both the detail and accuracy may be relaxed somewhat far away from the site(s)."


For the distant part of the map I could add that large areas are more important than small ones, and areas with significantly different roughness (water, forest) are more important than areas with a slight variation form the average.


WAsP simplifies your detailed roughness map to a roughness rose for each point of calculation. This roughness rose is divided into the usual number of sectors and each sector has a relatively small number of roughness zones, which are used in the roughness change model. The default maximum number of zones is 10. The roughness in these zones are area-weighted averages based on your detailed map, so a small distant patch makes little difference. There is more explanation of this roughness map simplification in the European Wind Atlas.