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1. Introduction
Appendix MM1 Mini-manual 1: The Department of Trade and Industry wind speed database (ETSU NOABL) contains estimates of the annual mean wind speed throughout the UK. The data is the result of an air flow model that estimates the effect of topography on wind speed. There is no allowance for the effect of local thermally driven winds such as sea breezes or mountain/valley breezes. The model was applied with 1km square resolution and makes no allowance for topography on a small scale or local surface roughness (such as tall crops, stone walls, or trees), both of which may have a considerable effect on the wind speed. The data can only be used as a guide and should be followed by on-site measurements for a proper assessment. The programme is installed in Start > Programs > AEA Technology > UK Wind Speed Database Extractor, When you run it choose the View > Great Britain menu option. The database uses the Ordnance Survey grid
system for both Great Britain and Northern Ireland. The grid reference
given is for the bottom left corner of each square and is based on the
Ordnance Survey National Grid system. The value for each site square is
given in bold. The grid references are based on the full Ordnance Survey
grid system, although most people use the encoded version. The encoded
version uses two letters and four digits for each kilometer square whereas
the long version uses six digits, e.g., This is because 100km grid square ST has co-ordinates 300km East, 100km North and NY has co-ordinates 300km E, 500km N. You can get appropriate site grid references quite easily from an Ordnance Survey road atlas (they are usually accurate enough). The programme gives you a screen like the one above. By typing in the 2-letter code in the top left box and then the two-digit easting and northing in the next two boxes to the right, the system will automatically convert these to the three digit numerical x and y co-ordinates refereed to above. To get the data once the coordinates are correctly entered and converted, simply click the blue button on the top right. The data is then automatically loaded for that reference plus the eight kilometre cells around it for each of the three heights in turn. Each value stored in the database is the estimated average for a 1km square at either 10m, 25m or 45m above ground level (agl). Make a note of all the data making sure you have the correct data for each point. This is a little complicated but you will learn pretty quickly how it works. The ETSU NOABL wind speed data needs to be stored in ASCII (text) format. This is good for GIS purposes because we actually enter the data as a three-column spreadsheet with x, y and a z value which represents the modeled wind speed at that specific point on a 100 metre grid. Typically it will look like this; x y z You will notice that the x and y co-ordinates have just been multiplied by 1,000 to make them match ArcView formats when you import them subsequently. You can do this easily enough in a spreadsheet. In this form it can be saved as either a .txt or .dbf file which are the formats required by ArcView. We can then open up the table in ArcView and use the VIEW > ADD EVENT THEME command to load it in as a point file. Once loaded it will need to be converted into a shape file. The Add Event Theme is an incredibly valuable command for data entry and conversion and can be used with any numerical data set that contains columns representing geographical references. These columns can be anything from a simple integer to an earth surface co-ordinate expressed in degrees and minutes. Obviously the view you are converting to will aid this geo-referencing process. We will be able to import the files produced by the DTI Wind Speed database because we are expressing them as 6 digit co-ordinates, the form we know our view is set up in. HINT: To save yourself doing a lot of data entry only to find you have chosen the wrong area, select a single grid reference for which you will get eight point values. Create a simple 9 row x,y,z file as above and add to the GIS with one or two of your vector road or urban files loaded. This will show you very quickly if you have got the referencing write and help you work out how to do it correctly if you've got it wrong. DISCLAIMER The ETSU NOABL wind speed data is provided free of charge
and is not warranted as suitable for any particular purpose or use. The
User shall assume full responsibility for his use of the data. |
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prev | next | back to top Last updated: December 4, 2003
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