Campbell Scientific CSAT3 3-D Sonic Anemometer - Manual (Page 11)

CSAT3 Three Dimensional Sonic
Anemometer
1. General
The CSAT3 is an ultrasonic anemometer for measuring wind speed in three
dimensions. It uses three pairs of non-orthogonally oriented transducers to
sense the horizontal wind. Each pair of transducers transmits and receives the
ultrasonic signal. The time of flight is directly related to the wind speed along
the sonic transducer axis. The speed of sound is directly related of the air
density, e.g. temperature and humidity.
The CSAT3 can be used to measure average horizontal wind speed and
direction or turbulent fluctuations of horizontal and vertical wind. From the
turbulent wind fluctuations, momentum flux is calculated. By finding the
covariance between vertical wind and scalars, sensible, latent heat, carbon
dioxide flux is directly be measured.
The sonic transducers are sealed and will not be damaged should they become
wet. The CSAT3 will continue to make wind measurements under rainy
conditions; however, like all ultrasonic anemometers, should the transducers be
sufficiently obscured, the CSAT3 will be unable to make further
measurements.
The CSAT3 can be measured using SDM (Synchronous Device for
Measurements) communications and a Campbell Scientific, Inc. datalogger.
All Campbell Scientific dataloggers that support the CSAT3 SDM instruction
do so without a special operating system with the exception of the 21X and
CR10, see TABLE 6-2 for compatible dataloggers.
The fine wire thermocouple used with the CSAT3 is the FW05. It is a 0.0005-
inch diameter thermocouple mounted on a stainless steel bayonet. A FWC-L35
cable is required with the FW05. Four feet of the FWC-L35 is bundled inside
the enclosure to minimize conduction of heat into the terminal strips. The
remaining 31 feet permits mounting the FW05 to the side of the CSAT3 head.
Finally, the thermocouple cover (pn 10080) is placed over the connectors. This
cover is used to mount the connectors to the side of the CSAT3 head and
minimize the temperature gradient across the omega brand connectors.
2. Specifications
2.1 Measurements
The CSAT3 measures wind speed and the speed of sound along the three non-
orthogonal sonic axes. The wind speeds are then transformed into the
orthogonal wind components u
x
, u
y
, and u
z
and are referenced to the
anemometer head; the reported speed of sound (c) or sonic virtual temperature
(T
s
), is the average between the three non-orthogonal sonic axes. The errors
caused by wind blowing normal to the sonic path are corrected online before
the wind speed is transformed into orthogonal coordinates. It is not necessary
to apply the speed of sound correction described by Liu et al., 2001. The
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