Vaisala WINDCAP WS425 Guide de l'utilisateur télécharger pdf (Page 40)

User's Guide ______________________________________________________________________

The vectors are calculated as follows:

)A/1(1/A5.0V

21a

−⋅⋅=

(1/A

−

⋅

)A/1(1/A 5.0V

−⋅⋅=

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°.

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Vaisala WINDCAP WS425 Guide de l'utilisateur Page 40