Roughness Analysis (RA)
RA stands for Roughness Analysis and is used to provide our onshore wind users with an up to date, digital map of the roughness length of the earth’s surface based on the land cover present. The RA is used by our onshore wind users as a critial input to their wind simulation models.
A Spottitt RA has 10m resolution, is derived from a Spottitt Land Cover Analysis (LCA), and takes about 1 hour to generate for any location globally. In-face the resolution and detail can be too great for some wind simulation software packages to handle, but we have tools built in to Spottitt to help with that. See full product specifications below.
This is part of an RA done in Thailand. View the full analysis and base LCA used to generate it in Spottitt here.
Coverage – global
Source Data – self-service RA analyses is generated from a Spottitt LCA. Through the Spottitt geoportal you will be asked to select and source LCA, set your desired roughness length parameters per land cover class then set your RA analysis running. You will be informed by email and notification within Spottitt the moment your analysis is ready.
RA analysis resolution – 6m if derived from LCA based on SPOT/Landsat image pair, or 10m if derived from LCA based on Sentinel 2/Sentinel 2 image pair.
Minimum Mapping Unit (Roughness sieving parameter:) – Default setting in 25 pixles, this means that all polygons are 25 pixels or more in size. When setting up a RA you can choose to set this at 0, 250, 500, 1000, 2500 or 5000 pixels. Why might you want to generate a sieved RA? Sieving can be used to reduce the “complexitiy” of the results, as well as the weight of the file and wind simulation processing times by removing polygons smaller than the chosen number of pixels. e.g., when choosing “25”, all polygons below 25 pixels are reclassified based on the class of the largest neighbouring polygon . Please see Spottitt manual for relevant visual examples.
Viewing your RA anlaysis and source LCA – Interactively via the Spottitt geoportal, no special GIS software required.
Editing your RA anlaysis – polygon roughness length allocation and polygon deletion, addition and outline editing can be done via the Spottitt geoportal, no special GIS software required.
Standard RA anlaysis legend – 10 roughness length classes determined by user.
Exporting your RA anlaysis – all Spottitt anlayses can be downloaded in .shp file format for easy export to GSI software packages and .dxf for export to AutoCAD. You can also export what you see in the Spottitt geoportal with legend for inclusion in reports in many formats including .jpg, .doc, .pdf and more.
Exporting your RA anlaysis for use in WaSP based wind simulation software packages – RA can also be converted into .map file format for easy export to WaSP based wind simulation software packages. During the .map conversion process you will be asked to define your desired level of polygon generalization (any whole number between 0 and 10) meters. This setting is used to generalize all polygons by making the minimum distance between each data point around the polygon the chosen number of meters. This is an effective method to reduce file size and therefore wind analysis processing times without reducing the complexity of your RA in the way that sieving does.