
ZENO
®
-3200 USER MANUAL
Coastal Environmental Systems (206) 682-6048 Page D-12
22
11
2
11
i
i
i
i
,
with
i
defined such that each
i
is the smaller of |
i
-
V
| and 2-|
i
-
V
|. Calculating this exactly requires
two passes over the data: first to calculate
V
, and then to find
. The ZENO uses a single pass method
so that data can be processed in real time without storing all the wind samples in memory. Yamartino
321
compared several single pass computations and showed that the most accurate equation, which is used in
the ZENO, is as follows:
22
3
1
3
2
1arcsin
YX
The maximum wind gust (output 7) is computed from a 1 to 5 second running average of the wind speed.
On each pass, the running average gust is computed and compared to the current maximum value. If the
new gust average is larger than the previous gust average, then the current gust is recorded as the latest
maximum gust. The gust is reset at the start of each sample interval time.
2.2. Running Wind Vector Average Process
Inputs: 4 Wind Speed (D)
5 Wind Direction (D)
6 Optional Compass Input (D)
7 Gust Sample Window, 1 to 5 seconds (U)
8 Running Average Time in Minutes (U)
9 Percent Valid Data (U)
Outputs: 1 Vector Average Wind Speed
2 Vector Average Independent Wind Direction
3 Average Scalar Wind Speed
4 Most Recent Wind Speed
5 Most Recent Wind Direction
6 Sigma-theta
322
7 Maximum Wind Gust
8 Average U vector
9 Average V vector
10 Most Recent Compass Reading
11 Running Vector Average Wind Speed
12 Running Vector Average Independent Wind Direction
13 Running Average Sigma-theta
14 Running Maximum Wind Gust Speed
321
R. J. Yamartino: "A Comparison of Several 'Single-Pass' Estimators of the Standard Deviation of Wind
Direction", Journal of Climate and Applied Meteorology, Volume 23
. American Meteorological Society, 1984.
Pp. 1362-1366.
322
Sigma-theta is the approximate Standard Deviation of the wind direction using the Yamartino equation. Refer to
the Vector Average Wind Process for details regarding this equation.
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