Experimental
Setup
|
|
|
|
 |
Experimental Setup
|
The system uses the eddy covariance method to obtain fluxes of momentum, sensible heat, water vapour and CO2. Fluctuations in CO2 and water vapour concentrations are measured at a sampling frequency of 10 Hz using an infra-red gas analyser (LICOR 6262) in closed-path mode. Air is drawn from the 3.5 m measurement height along a 5 m, insulated and heated sample tube to the gas analyser using two 12VDC Brailsford pumps, at a rate of 6 litres/min. The gas analyser is calibrated every 24-hours by automatic shunting of bottled zero and span gases to the intake end of the sample line, with solenoid valves under the control of a datalogger. A Campbell Scientific Inc. (CSI) CSAT3 sonic anemometer measures 3 dimensional components of windspeed and air temperature at 10 Hz. A CSI krypton hygrometer (KH2O) is used to provide verification of water vapour fluxes and as a check for calculated sample tube delay times. A dew point hygrometer (General Eastern, Dew-10) provides a reference humidity measurement.
sample tube, at 3.5m height above the Sporadanthus canopy.
flows, inside the hut. Standard meteorological instruments measure relative humidity, air temperature, windspeed, soil heat flux, soil temperature, along with solar, photosynthetically active and net radiation flux densities. Leaf wetness sensors provide an index of canopy wetness. CR10X dataloggers are used for all measurements. A Dataflow capacitance probe measures water table elevation. Power demand is less than 50 W at 12 VDC and is maintained from an array of ten 80 W solar panels.
Solar panel array. A CSI CR10X datalogger measures raw signals from the gas analyser, sonic anemometer and KH20 at 10 Hz frequency. Data are passed up to a Toshiba 320CDS notebook computer where a data acquisition and diagnostic system are run under Matlab 5.2. The data aquisition system shows 1-minute means of raw signals and accesses graphical tools to view raw high-frequency data, calibration data and time-series' of approximate half-hourly fluxes. Data are stored in time-stamped binary files (34 MB per day) and transferred to tape drive (SONY Ditto). At fortnightly fieldsite visits tapes are retrieved and binary data copied to CD-ROM before flux calculations and post processing are carried out using Matlab.
Computer, gas analyser and tape drive used for data acquisition,
Data acquisition screen using Matlab GUI capabilities. Three CSI CR10X dataloggers are employed for control functions and storage of low-frequency data. One CR10X controls calibrations and power supply to the tape drive, laptop PC, sample-tube heater, and cellphone. Campbell Scientific Inc PC208W software runs scheduled downloads from dataloggers, while pcAnywhere (Symantec) allows remote diagnosis of system activity.
CR10X dataloggers are used for all measurement Information on some of the equipment used in this experiment can be found via links on the Resource and Links page.
The next section shows Example raw data from this experiment.
|
