| Re: gaussian air dispersion model [message #46503] |
Sun, 27 November 2005 17:27  |
Mark Hadfield
Messages: 783
Registered: May 1995
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Senior Member |
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guillaume.drolet.1@ulaval.ca wrote:
> Hi Mark,
>
> The following comes from N. Kljun. She developed the footprint model:
>
> "...you'll get the along-wind extent, but it's a crosswind-integrated
> model (no y-information).
> the full model gives you the y-information, but is not easy to be
> applied and it will be extremely time-consuming to run it for that many
> cases as you will have to.
> it'll be easier to estimate the y-extent using a simple gaussian
> dispersion function."
>
> I'm sorry, I made a mistake in my first post: I need to estimate the
> 'across-wind' extent (y-extent), and NOT the 'along-wind' (x-extent),
> which will be given by the model.
So are you going to estimate the cross-wind-integrated ground level
concentration with the footprint model and the across-wind variation in
concentration with a gaussian function? In which case you will need an
estimate of across-wind width vs downwind distance (sigmay as a function
of x). How are you going to estimate that?
> For this simple model, the following inputs are needed:
>
> zm = Measurement height [m]
> znot = Roughness length [m]
> h = Boundary layer height [m]
> sigmaw = sigmaw [m s-1]
> ustar = u* [m s-1]
> r = Percentage to be included [%]
>
> Some inputs are available from flux towers measurements
> (zm,sigmaw,ustar) while others are estimates (znot,h). The outputs are:
>
> xmax: location of maximum influence for the location
> xr :distance from receptor which include r% of the area contributing
> to the measured flux.
By "this simple model" you mean the footprint model, right?
> Is that enough information? For more details on the model, see:
> http://footprint.kljun.net
I've looked at the URL, but not read the paper. It sounds like the
footprint model is a simple set of formulae. Do you plan to implement
this in IDL? Shouldn't be too hard.
So where do you want help?
--
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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