Campbell CR7 Manuál s instrukcemi stáhnout pdf (Strana 114)

SECTION 11. OUTPUT PROCESSING INSTRUCTIONS

11-2

minutes, the standard deviation is calculated

from all 3600 scans when the sub-interval is 0.

With a sub-interval of 900 scans (15 minutes),

the standard deviation is the average of the four

sub-interval standard deviations. The last sub-

interval is weighted if it does not contain the

specified number of scans.

There are three Output Options, which specify

the values calculated.

Option 0:

Mean horizontal wind speed, S.

Unit vector mean wind direction, θ1.

Standard deviation of wind direction, σ(θ1).

Standard deviation is calculated using the

Yamartino algorithm. This option complies

with EPA guidelines for use with straight-

line Gaussian dispersion models to model

plume transport.

Option 1:

Mean horizontal wind speed, S.

Unit vector mean wind direction, θ1.

Option 2:

Mean horizontal wind speed, S.

Resultant mean wind speed, U.

Resultant mean wind direction, θu.

Standard deviation of wind direction, σ(θu).

This standard deviation is calculated using

Campbell Scientific's wind speed weighted

algorithm.

Use of the resultant mean horizontal wind

direction is not recommended for straight-

line Gaussian dispersion models, but may

be used to model transport direction in a

variable-trajectory model.

Measured raw data:

S

i

= horizontal wind speed

θ

i

= horizontal wind direction

Ue

i

= east-west component of wind

Un

i

= north-south component of wind

N = number of samples

Calculations:

Scalar mean horizontal wind speed, S:

S=(ΣS

i

)/N

where in the case of orthogonal sensors:

S

i

=(Ue

i

2

+Un

i

2

)

1/2

Unit vector mean wind direction, θ1:

θ1=Arctan (Ux/Uy)

where

Ux=(Σsin θ

i

)/N

Uy=(Σcos θ

i

)/N

or, in the case of orthogonal sensors

Ux=(Σ(Ue

i

/U

i

))/N

Uy=(Σ(Un

i

/U

i

))/N

where U

i

=(Ue

i

2

+Un

i

2

)

1/2

Standard deviation of wind direction, σ(θ1),

using Yamartino algorithm:

σ(θ1)=arc sin(ε)[1+0.1547 ε

3

]

where,

ε=[1-((Ux)

2

+(Uy)

2

)]

1/2

and Ux and Uy are as defined above.

Resultant mean horizontal wind speed, U:

U=(Ue

2

+Un

2

)

1/2

where for polar sensors:

Ue=(ΣS

i

Sin θ

i

)/N

Un=(ΣS

i

Cos θ

i

)/N

or, in the case of orthogonal sensors:

Ue=(ΣUe

i

)/N

Un=(ΣUn

i

)/N

Resultant mean wind direction, θu:

θu=Arctan (Ue/Un)

Standard deviation of wind direction, σ(θu),

using Campbell Scientific algorithm:

σ(θu)=81(1-U/S)

1/2

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