Vaisala WMT700 - Manual (Page 40)

User's Guide ______________________________________________________________________
The vectors are calculated as follows:
) A / 1 (1/A 5 . 0 V
2 1 a
− ⋅ ⋅ =
a
L
) A / 1 (1/A 5 . 0 V
4 3
− ⋅ ⋅ =
b b
L
) A / 1 (1/A 5 . 0 V
6 5
− ⋅ ⋅ =
c c
L
The equation depends on the accurate distance of the
measurement path (L). The computed wind speeds are
independent of altitude, temperature, and humidity, which are
canceled out when the transit times are measured in both
directions, although the individual transit times depend on these
parameters.
Coordinate Systems: Vector and Polar
Calculations
The triangular geometry of the sensor is converted to orthogonal
coordinates to achieve the x and y components. Then the sensor
converts the wind vectors into polar coordinates.
The measurement results are reported as follows:
- WMT700 reports WS (x, y) as two scalar speeds, one parallel
to the N-S direction (x) and the other (y) parallel to the W-E
direction. The speed unit may be m/s, kt, mph, or km/h.
x = WS × cos (WD)
y = WS × sin (WD)
- WMT700 reports polar wind speed as a scalar speed in
selected units (m/s, kt, mph, km/h).
Polar wind direction is expressed in degrees (°). WMT700
indicates the direction that the wind comes from. North is
represented as 0°, east as 90°, south as 180°, and west as 270°.
38 ___________________________________________________________________ M211095EN-E