FREddyPro (version 1.0)

Average: Average flux footprint

Description

Calculate the average flux footprint from an array of half hourly turbulance data using Kormann and Meixner 2001 model.

Usage

Average(fetch = 500, height = 3, grid = 200, speed, direction, uStar,
zol, sigmaV, weights = NULL)

Arguments

fetch

The upwind distance over which you want the calculation domain to extend. Note that the footprint will be normalized to that domain so footprints that extend well beyond the domain will be overrepresented in

height

The z-d height of the flux system

grid

The total calculation grid size. The default is 200 which would mean the footprint would be represented in a 200x200 array corresponding to dimensions of two times the fetch on each side of the grid.

speed

An N length array of wind speeds at the flux system

direction

An N length array of wind directions at the flux system

uStar

An N length array of friction velocities

zol

An N length array of Monin Ohbukov stability parameters

sigmaV

An N length array of standard deviations of the cross-stream wind component

weights

A dictionary of N length arrays footprint weighting values. This is an optional input

Value

Output is a list object with a 3 elements including:Probability: the array holding the footprint probabilities Fpn: the array holding the grid point distance north of the flux system Fpe: the array holding the grid point distance east of the flux system WeightedProbability: the array holding the weighted footprint probabilities

References

Kormann, R., and Meixner, F.X. (2001). An analytical footprint model for non-neutral stratification, Boundary-Layer Meteorology. 99, 207-224.

Examples

## Load the data
data(fluxes)

## Clean fluxes
fluxes=cleanFluxes(fluxes,sdCor=TRUE,sdTimes=3,timesList=3,distCor=TRUE,
                   thresholdList=list(H=c(-100,1000),LE=c(-100,1000)))

## Use data without NA values
fluxes_noNA<-fluxes[which(!is.na(fluxes$L)),]

## Displacement height
d=17.42

## Calculate z
fluxes_noNA$z=(fluxes_noNA$X.z.d..L*fluxes_noNA$L)+d

## Calculate zol
fluxes_noNA$zol=fluxes_noNA$z/fluxes_noNA$L

## Calculate average footprint
footprint=Average(fetch=500,height=33,grid=200,fluxes_noNA$wind_speed[180:183],
fluxes_noNA$wind_dir[180:183],fluxes_noNA$u.[180:183],fluxes_noNA$zol[180:183],
sqrt(fluxes_noNA$v_var[180:183]))

## You can also use the plot.footprint function of FREddyPro to plot the result
plotFootprint(footprint)