Campbell Scientific Open Path Eddy Covariance (OPEC) - Manual (Page 12)

OPEC Open-Path Eddy-Covariance System
2.1 Fetch and
local surface layer. The local surface
layer grows at a rate of approximately 1 vertical meter per 100 horizontal
ng
tion
n and the second with 0.5 m soybean. Eddy-
Covariance sensors mounted at 2 m above the corn field should have a
minimum of 200 m of fetch in all the directions that the data is of interest,
particularly between the eddy-covariance sensors and the interface between the
2.2 Mounting
The IRGASON is mounted to a tripod or tower using a horizontal mounting
a leveling mounting kit (CM250). Section 3 of the
l contains detailed information on mounting the sensors and
2.2.1 Measure So
e station operator must enter
the negative x-axis azimuth of the sonic into the program variable
prevailing
a compass
is (prevailing wind).
Don’t forget to account for the magnetic declination at the site;
Sensor Height
The eddy-covariance sensors must be mounted at some height to ensure that
the measurements are made within the
meters. Thus, a height to fetch (horizontal distance travelled) ratio of 1:100
may be used as an absolute bare minimum rough rule of thumb for determini
the measurement height.
The fetch should be homogenous and flat, and no abrupt changes in vegeta
height should exist (Tanner, 1988). Consider two adjacent fields, the first
planted with 1 m tall cor
corn and soybean field.
arm (CM20x) and
IRGASON manua
EC100 electronics.
nic Azimuth
To compute the correct compass wind direction, th
“sonic_azimuth”. If the sonic is installed such that it points into the
wind, the negative x-axis is pointing into the prevailing wind. Take
azimuth of the negative x-ax
NOTE
see Appendix A for details.
2.3 Wiring
ntific Open-Path Eddy-Covariance system can take on several
configurations and utilize several different dataloggers. It is impractical to
document the different wiring schemes in this manual. However, each custom
datalogger program (p/n 18442 or 18443) ships with a complete and detailed
2.4 Power
The system requires about 1.5 to 6 W continuous power, depending on the
atalogger and sensor configuration. The approximate power requirements of
various key components, for a system running at 10 Hz, are listed in TABLE
2-1, TABL
A Campbell Scie
wiring diagram.
d
E 2-2, and TABLE 2-3.
4