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Distance Decay Function   Peter Iles Apr 08, 2002
Re: Distance Decay Function   Stephen Gardoll Apr 12, 2002
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Subject Distance Decay Function 
Author Peter Iles 
Date Apr 08, 2002 
Message I am looking at the visual impact of a potential windfarm site for a colege project. I have calculated the viewshed for the wind turbines but want to add a factor that takes account of the apparent size of the turbines, i.e. that if you are a long way away, the turbines seem small and the visual impact is less and if you are close the turbines seem larger and the impact is corespondingly larger. A quick back-yard experiment apparently shows that the 'distance decay factor' is not linear as I expected but a reverse curve (and I don't know how to work out its equation!)

Has anyone seen anything about this, or got an extension/tool/cunning wheeze to help? 
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Subject Re: Distance Decay Function 
Author Stephen Gardoll 
Date Apr 12, 2002 
Message 1. Calculate the distance away from each turbine (find distance). Calculate the log10, or inverse distance squared etc ... to get the decay. Modify values to get the way you want (* or / by a constant)

2. If the turbines are different sizes. Add a field of magnitude (turbine A is 2, Turbine B is 1 ... A is twice the size of B). Calculate the Analysis-Assign Promity based on the new magnitide field.

3. Mutiple the magnitude grid (2) by decay (1) to get result.


If the turbines are close together, then you will have to do each seperately. Then get the maximum value from each of the resulting grids to get final noise pollution. This result will look better, because the noises will overlap.

For a cool effect final effect (presentation wise), scan in a base map and in 3D analysis display the sound pollution as a 3D object (bubble) above the scan. Set to 50% transparent. Looks impressive that way.

Good luck :D
  ------- Stephen J. Gardoll
------ Research Officer
----- Centre for Global Metallogeny
---- Department of Geology and Geophysics
--- University of Western Australia
-- 35 Stirling Highway Crawley WA Australia, 6009
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