Campbell Scientific CR1000 Measurement and Control System - Manual (Page 189)

Section 7. Installation
189
Table 29. OutputOpt Options
Option Description (WVc() is the Output Array)
0
WVc(1): Mean horizontal wind speed (S)
WVc(2): Unit vector mean wind direction (Θ1)
WVc(3): Standard deviation of wind direction
σ(Θ1). 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.
1
WVc(1): Mean horizontal wind speed (S)
WVc(2): Unit vector mean wind direction (Θ1)
2
WVc(1): Mean horizontal wind speed (S)
WVc(2): Resultant mean horizontal wind speed (U)
WVc(3): Resultant mean wind direction (Θu)
WVc(4): Standard deviation of wind direction σ(Θu). 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.
3 WVc(1): Unit vector mean wind direction (Θ1)
4
WVc(1): Unit vector mean wind direction (Θ1)
WVc(2): Standard deviation of wind direction σ(Θu). 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.
7.8.5.2 Wind Vector Processing
WindVector() uses a zero-wind-speed measurement when processing scalar wind
speed only. Measurements at zero wind speed are not used in vector speed or
direction calculations (vectors require magnitude and direction).
This means, for example, that manually-computed hourly vector directions from
15-minute vector directions will not agree with CR1000-computed hourly vector
directions. Correct manual calculation of hourly vector direction from 15-minute
vector directions requires proper weighting of the 15-minute vector directions by
the number of valid (non-zero wind speed) wind direction samples.
Note Cup anemometers typically have a mechanical offset which is added to each
measurement. A numeric offset is usually encoded in the CRBasic program to
compensate for the mechanical offset. When this is done, a measurement will
equal the offset only when wind speed is zero; consequently, additional code is
often included to zero the measurement when it equals the offset so that
WindVector() can reject measurements when wind speed is zero.
Standard deviation can be processed one of two ways: 1) using every sample
taken during the data storage interval (enter
0 for the Subinterval parameter), or 2)
by averaging standard deviations processed from shorter sub-intervals of the data-
storage interval. Averaging sub-interval standard deviations minimizes the effects
of meander under light wind conditions, and it provides more complete
information for periods of transition (see EPA publication "On-site
Meteorological Program Guidance for Regulatory Modeling Applications").