SRTM on WAsP Map Editor

[carriv9]

Good Afternoon,

I have a couple quick questions about WAsP Map Editor. First of all, I usually use the "Import->SRTM Database" tool to gather my topographic maps, this being said I have mostly used a 5-m contour Equidistance in the past. My question is, what would be the downsides of using a lower equidistance (ex. 1-m), besides the computing power, would there be any other significant effect on my analysis? Will the calculation be "more" accurate? Also, what version of SRTM does WaSP Map Editor use?

Thank you!

[Morten]

Good morning,


Contours with 5-m vertical separation could be a good general choice, but unless you are very pressed for time you should also inspect the result in the map image and maybe make some adjustments. Try to zoom in and check whether the generated contours have lots of parallel line segment in the cells of the original SRTM map. If so, you could probably do with less vertical separation as WAsP will get almost the same height information when it interpolates your contour map. On the other hand, you risk losing information on hill top if you set the vertical separation too low, e.g. to 20m – that is unless you manually add exact spot-height information in the map editor, which actually is recommended. Read more in the http://www.wasp.dk/support-and-services sections called ‘maps’, ‘SRTM-maps’ and maybe also at http://www.wasp.dk/support-and-services/faq#weng__working-with-maps-in-weng


The horizontal length scales of the terrain features is also important for the flow at hub height. The near-surface flow will always follow the terrain, but undulations with small horizontal length scales will have less influence on the flow at hub height than undulations with a long length scale. So you might need less vertical resolution lower in a landscape with big round hills.


A very large contour map fill will slow down the WAsP map pre-processing. A good tip is to have more resolution near the points of interest than at far distance. You can do this with the map editor, e.g. by inserting a high resolution map for the wind-farm area inside a map generated from SRTM downloads.


Click ‘File> Import>SRTM’ in the map editor to open a SRTM download window. This has ‘File location’ at the top from where it is possible to change the SRTM download link or use maps stored locally. The default link is https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/ which point towards version 2 maps. You can also work with version 3 maps, but then you need to register at NASA and log in with a user name before you download with the Map Editor. Read more about this in the Map Editor help file.


Cheers,
Morten