Vaisala WINDCAP WS425 User's Guide download pdf (Page 30)

USER'S GUIDE____________________________________________________________________

28 __________________________________________________________________ M211095EN-C

The vectors are calculated as follows:

)A/1(1/A5.0V

21a





)A/1(1/A5.0V





)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 cancelled 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

Triangle 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 User's Guide Page 30