back to autochamber: a sonic topology

"Our main research goal is to measure the net exchange (i.e., movement) of
atmospheric carbon dioxide between the prairie and the atmosphere. We want
to determine how different land management factors (burning, grazing,
forestation) might affect the carbon balance of the ecosystem. This is of
great interest because the land surface may have the potential to sequester
(store) some of the excess CO2 were are adding to the atmosphere via fossil
fuel combustion. Thus, we may be able to help stave off climate change
using good land management policy.

We measure the movement of CO2 between theprairie and the atmosphere using a method called eddy covariance.

This technique requires two instruments:
a sonic anemometer and an open-path CO2 analyzer. The sonic anemometer
measures the velocity of air in all three Cartesian coordinates by
measuring the speed of sound between paired transceivers. Data are
collected very rapidly (10 times per second). These data are coupled with
results from the gas analyzer (also collecting data 10 times per second) to
calculate the number of CO2 molecules moving vertically above the surface
(towards the surface or away from the surface).

The quality of the eddy covariance data are tested in several ways, including: tests

for energy balance closure, plots of friction velocity vs. flux during the night, and direct comparison of

the tower fluxes to the autochambers during the night and dormant season. The autochambers measure total ecosystem respiration.

We operate three automated surface chambers along a 100-m east-west transect about 50 m south of each eddy covariance tower (9 chambers total). Measurements of ecosystem respiration is made at 1 hour intervals during periods of high flux (summer) and 4-hr interval during the winter. Chambers are 0.85 m x 0.85 m x 0.25 m (length x width x height) in dimension and fabricated from 3.2-mm-thick aluminum plate. ...The edges of the chamber frame land on a soil collar that is permanently installed around the sample plot. A diaphragm pump mounted inside of the chamber headspace pumps air at 2.3 L min-1 from the chamber to the gas analyzer and then back to the chamber in a closed loop."

--Jay Ham, PhD., agronomist, climatologist, Kansas State University

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