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Re: gaussian air dispersion model [message #46572 is a reply to message #46529]

Mon, 28 November 2005 16:04

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

guillaume.drolet.1@ulaval.ca wrote:
> [snip]
> The footprint model will give me one dimension: the distance of the
> footprint in the mean wind direction, for a given measurement period
> and a given percentage (r) to be included. This distance will be the
> major-axis of the ellipse. The length of the ellipse's minor-axis (i.e.
> across-wind width) will be missing and this is what I want to estimate
> with a gaussian function. How I will do that, honestly, I don't know???
> This is where I need help.

Then you are probably asking these questions in the wrong forum.

But obviously the hard bit is calculating the width parameter to be used
in the Gaussian function. The usual assumption is

sigma-y = sigma-theta * x * f(x)

where x is downwind distance, sigma-theta is standard deviation of wind
direction (in radians) and f(x) is a function that equals 1 at short
distances and then slowly drops away. If the distances in question are
small you can get away with

sigma-y = sigma-theta * x

Do you have any info on sigma-theta?

> As I said before, I need a way to estimate the 'across-wind width',
> knowing the 'along-wind extent' and other variables measured by the
> tower sensors (e.g., mean wind direction (x,y,z), etc.). I don't have a
> clue how I'm gonna find this but one thing is sure, I'm gonna need help!

You're going to need to do a bit of reading.

--
Mark Hadfield "Kei puwaha te tai nei, Hoea tahi tatou"
m.hadfield@niwa.co.nz
National Institute for Water and Atmospheric Research (NIWA)

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[Message index]

		gaussian air dispersion model By: guillaume.drolet.1 on Thu, 24 November 2005 08:48
		Re: gaussian air dispersion model By: guillaume.drolet.1 on Tue, 29 November 2005 06:56
		Re: gaussian air dispersion model By: K. Bowman on Tue, 29 November 2005 06:27
		Re: gaussian air dispersion model By: David Fanning on Mon, 28 November 2005 20:28
		Re: gaussian air dispersion model By: Mark Hadfield on Mon, 28 November 2005 20:00
		Re: gaussian air dispersion model By: guillaume.drolet.1 on Mon, 28 November 2005 19:18
		Re: gaussian air dispersion model By: Mark Hadfield on Mon, 28 November 2005 16:04

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