Appendix B. CSAT3BH
measurement theory
B.1 Theory of operation
B.1.1 Wind speed
Each axis of the CSAT3BH pulses two ultrasonic signals in opposite directions. The time of flight
of the first signal (out) is given by:
Eq. 1
and the time of flight of the second signal (back) is given by:
Eq. 2
where:
t
o
= time of flight out along the transducer axis
t
b
= time of flight back, in the opposite direction
u
a
= wind speed along the transducer axis
d = distance between the transducers
c = speed of sound
The wind speed (u
a
) along any axis can be found by inverting the preceding relationships, then
subtracting
(p. 95) from
(p. 95) and solving for u
a
.
Eq. 3
The wind speed is measured on all three non-orthogonal axis to give u
a
, u
b
, and u
c
, where the
subscripts a, b, and c refer to the non-orthogonal sonic axes.
CSAT3BH Three-Dimensional Heated Sonic Anemometer
95
