Campbell Scientific CR23X Micrologger - Manual (Page 182)

SECTION 11. OUTPUT PROCESSING INSTRUCTIONS
11-2
There are three Output Options that specify the
values calculated.
Option 0:
Mean horizontal wind speed, S.
Unit vector mean wind direction,
Θ
1.
Standard deviation of wind direction,
σ
(
Θ
1).
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,
Θ
1.
Option 2:
Mean horizontal wind speed, S.
Resultant mean wind speed, U.
Resultant mean wind direction,
Θ
u.
Standard deviation of wind direction,
σ
(
Θ
u).
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=(
Σ
S
i
)/N
where in the case of orthogonal sensors:
S
i
=(Ue
i
2
+Uni
2
)
1/2
Unit vector mean wind direction,
Θ
1:
Θ
1=Arctan (Ux/Uy)
where
Ux=(
Σ
sin
Θ
i
)/N
Uy=(
Σ
cos
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,
σσσσ
(
Θ Θ Θ Θ
1),
using Yamartino algorithm:
σ
(
Θ
1)=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=(
Σ
S
i
Sin
Θ
i
)/N
Un=(
Σ
S
i
Cos
Θ
i
)/N
or, in the case of orthogonal sensors:
Ue=(
Σ
Ue
i
)/N
Un=(
Σ
Un
i
)/N
Resultant mean wind direction,
Θ Θ Θ Θ
u:
Θ
u=Arctan (Ue/Un)
Standard deviation of wind direction,
σσσσ
(
Θ Θ Θ Θ
u),
using Campbell Scientific algorithm:
σ
(
Θ
u)=81(1-U/S)
1/2
*** 70 SAMPLE ***
FUNCTION
This instruction stores the value from each
specified input location. The value(s) stored are
those in the input location(s) when Instruction
70 is executed with the Output Flag set high.
PARAM. DATA
NUMBER TYPE DESCRIPTION
01: 4 Repetitions
02: 4 Starting input location no.
Outputs Generated: 1 for each repetition