The key components of each eddy flux tower are the gas analyzer and the omni-directional sonic anemometer. These are required for eddy covariance flux calculations. The gas analyzer measures CO2 and water content in the air, while the anemometer measures wind speed and direction of the air (e.g. a rotating eddy). As a simple example, if we assume an eddy at time 1 moves a parcel of air up over the land surface and it contains 3 molecules of CO2 and the eddy at time 2 moves a parcel of air down over the land surface and contains only 2 molecules of CO2, then we know that the net flux from time 1 to time 2 was upward, and equal to 1 molecule of CO2. This is the basic principle behind the eddy covariance method—covariance between the concentration of CO2 and vertical wind speed.
In addition to the gas analyzer and anemometer, each tower system also includes a suite of sensors often referred to as biometeorological or “biomet” sensors that measure radiative fluxes (albedo), as well as meteorological data such as temperature and humidity. The biomet sensors at each of the four flux towers include a net radiometer, soil temperature/humidity probes, soil thermistors, a rain gauge tipping bucket and a quantum sensor. Raw data measured by the gas analyzer and anemometer are logged directly to the analyzer interface unit; biomet data are logged to a separate data logger that is connected to the analyzer interface unit. In this way, all biomet data are integrated into the same data set collected by the analyzer and anemometer for gas flux calculations.
Eddy Flux Network Sensors and Instrumentation:
Gas analyzer: LI-COR LI-7200 Enclosed CO2/H2O Analyzer
Omni-directional sonic anemometer: Gill Windmaster Sonic Anemometer
Gas analyzer interface unit: LI-7550 Analyzer Interface Unit
Net radiometer: Kipp & Zonen CNR4 four-component net radiometer
Quantum (PAR) sensor: LI-COR LI-190SL quantum sensor
Air temperature and humidity probe: Vaisala HMP155 Humidity and temperature probe
Tipping bucket rain gauge: Texas Electronics TR-525M Tipping bucket rain gauge
Soil temperature probe: LI-COR 7900-180 Soil thermistor
Soil moisture probe: Delta-T ThetaProbe ML2x soil moisture probe
Biomet data logger: Sutron 9210
Sensors Deployed:
All four sensors are located on UNH property or research tracts:
Kingman Farm hayfield, Madbury, NH: (43.1717056N, 70.9259111W)
Moore Fields corn, Durham, NH: (43.138508N, 70.960972W)
Thompson Farm Forest, Durham, NH: (43.108456N, 70.9522W)
West Edge parking lot, Durham, NH: (43.14207778N, 70.95426667W)
