Environmental Engineering Reference
In-Depth Information
Eddy-covariance monitoring is carried out by simultaneously meas-
uring CO 2 concentration and vertical wind speed at (nearly) the same
point and at high frequency. The covariation of concentration and upward
or downward wind speed allows one to determine a net vertical CO 2 fl ux
averaged over time and over an area related to the height of the tower.
This approach can detect processes such as photosynthesis of plants
and trees, decay of biological materials, and soil respiration. The detec-
tion of very small CO 2 leakage fl uxes from a sequestration site would
theoretically be possible, but the overprint of natural CO 2 cycling pro-
cesses must be measured and time-averaged over a few years to
develop a background curve in order to discern a leakage signal (e.g.,
Lewicki et al . [10.53]).
Figure 10.5.9 shows a photo of an eddy-covariance tower with vari-
ous instruments including an infrared gas analyzer (IRGA) and sonic
(a)
(b)
Figure 10.5.9 Eddy covariance method
(a) Photograph of an open path eddy covariance system, consisting of an ultrasonic
anemometer to measure 3D air fl ow and infrared gas analyser (IRGA) to measure
carbon dioxide. This system is situated at the top of a 20 m high tower above a for-
est. Image by Veedar from Wiki Commons: http://en.wikipedia.org/wiki/File:Eddy_
Covariance_IRGA_Sonic.jpg
(b) A cartoon of the turbulent eddies that the eddy covariance method measures along
with CO 2 concentration to estimate net vertical CO 2 fl ux. Diagram created by George
Burba : http://en.wikipedia.org/wiki/File:EddyCovariance_diagram_1.jpg
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