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The non-orthogonal wind speed components are then transformed into orthogonal wind speed
components (u
x
, u
y
, and u
z
) with the following:
Eq. 4
where:
A = a 3 x 3 coordinate transformation matrix that is unique for each CSAT3BH and is stored in
ROM memory
B.1.2 Temperature
The sonically determined speed of sound is given in
(p. 96) and was found from the sum of
the inverses of
(p. 95) and
(p. 95). The CSAT3BH corrects online for the effect of wind
blowing perpendicular to the sonic path. No additional off-line corrections are required as
suggested by Liu, Peter, and Foken (2001).
Eq. 5
The speed of sound in moist air is a function of temperature and humidity and is given by:
Eq. 6
where:
g
= ratio of specific heat of moist air at constant pressure to that at constant volume
P = pressure
r
= air density
R
d
= gas constant for dry air
T
v
= virtual temperature
T = air temperature
q = specific humidity defined as the ratio of the mass of water vapor to the total mass of air (as
in Kaimal and Gaynor 1991; Wallace and Hobbs 2006)
Note that
g
is a function of specific humidity. It would be convenient if the effects of humidity
could be consolidated into one term.
CSAT3BH Three-Dimensional Heated Sonic Anemometer
96