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7.1.3 Sonic transducer shadow correction
The CSAT3, CSAT3A, CSAT3B, and CSAT3BH suffer minimal wind distortion compared to many
other sonic anemometer designs because of a very low ratio of transducer diameter to sonic path
length, and because the non-orthogonal geometry keeps the sonic paths at angles closer to
perpendicular with respect to a mean horizontal wind flow. However, there are cases, such as
when oncoming wind has high angles of attack (for example, low frequency eddies on a tall
tower), that will lead to more shadowing. Accordingly, an optional wind shadow correction
specific to the CSAT3-series transducer diameter and sonic path length has been implemented in
the CSAT3BH OS versions 1.11 and newer.
This shadow correction, known as the Kaimal correction (Kaimal 1979; Horst, Semmer, and
Maclean 2015), is applied according to:
Where:
U
i
= the magnitude of the wind vector parallel to the sonic path without shadowing errors
i
= a placeholder index for
a
,
b
, or
c
, representing the three sonic paths
θ
i
= the angle between the three-dimensional wind vector and the wind vector component
along the a-, b-, or c-sonic path (see
The CSAT3BH embedded code improves the estimates of θ — and therefore the accuracy of the
correction — by iteratively applying the preceding correction three times for each measurement
of each sonic path. Since debate continues on the appropriateness of this and other shadow
corrections in turbulent versus laminar flows, the default of this setting is Disabled.
CSAT3BH Three-Dimensional Heated Sonic Anemometer
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