Campbell CR5000 Specifiche Pagina 125

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Section 6. Data Table Declarations and Output Processing Instructions
6-31
Resultant mean horizontal wind speed,
U
:
U
=(Ue
2
+Un
2
)
1/2
FIGURE 6.4-3. Mean Wind Vector
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, Θ
ΘΘ
Θu:
Θu=Arctan (Ue/Un)
Standard deviation of wind direction, σ
σσ
σ(Θ
ΘΘ
Θu), using Campbell Scientific
algorithm:
σ(Θu)=81(1-
U
/S)
1/2
The algorithm for σ(θu) is developed by noting (Figure 6.4-4) that
Cos U / s ; where
ii
(') '
ΘΘΘΘ
iii
u
==
FIGURE 6.2-3. Standard Deviation of Direction
The Taylor Series for the Cosine function, truncated after 2 terms is:
Cos ( ') ( ') /ΘΘ
ii
≅−12
2
U
Un
Ue
s
i
Θ'
i
Θ
u
U
i
U
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