Vaisala AWS330 - Scalar Wind Direction Average Method

Appendix B ______________________________________________________ Calculation Formulas
VAISALA______________________________________________________________________ 281
Scalar Wind Direction Average Method
Wind direction average calculation using the Scalar method is based on
the assumption that the source direction value does not differ more than
180 from the previous average value. The previous average value is
marked as 0 and the source values are scaled with respect to that point
so that the result varies between -180 and 180. For example, if the
previous average value was 10, a source value of 355 would be
converted to -15. This method is also used when the wind direction
maximum and minimum values are determined.
WD
s
= WD - WDA
prev
(instant table) (17)
WD
s
= WDAT - WDA
prev
(calculated table)



n
i
sis
nWDWDA
1
/)(
(18)
WDA = WDA
s
+ WDA
prev
(19)
where
WD = Wind direction instant value
WDAT = Wind direction average stored to data table
WD
s
= Wind direction instant value scaled with respect to the
previous average value
WDA
prev
= Previous wind direction average value, if defined;
otherwise the first source value
WDA
s
= Wind direction average value scaled with respect to the
previous average value
WDA = Wind direction average
n = Number of wind direction source values
Table 116 Inputs for Wind Calculation
Input Sensor
Wind speed Ws
i
See Table 3 on page 21
Wind direction WD See Table 3 on page 21