Campbell Scientific Wireless Sensor Network (CWB100, CWS220, and CWS900) - Manual (Page 61)

Appendix B. Measurement Names and Meanings
Scalar mean horizontal wind speed, S:
S=( Σs
i
)/N
where in the case of orthogonal sensors:
S
i
=(Ue
i
2 +Uni 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
FIGURE B.3-2. 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, Θu:
Θu=Arctan (Ue/Un)
B-5