Tower description

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46 m Tower Description

A 46 m, self-supporting tower with associated lab building, power, and communication lines was completed in June, 1998. At the end of June and in July 1998 the instrument booms, data loggers, communication and gas-flow lines, and the eddy correlation and radiation sensors were installed on the two main observation levels of the tower (46 m and 34 m, see the schematic representation of the tower set-up, below). The flow control system was installed in September and data collection on the top level started on September 22, 1998. The profile measurements of mean temperature, humidity and CO2 concentration through the canopy and up to the 46 m level on the tower was completed in March, 1999. Link to detailed list of tower intrumentation.

On each level on the tower the sensors (sonic, radiation components, temperature and humidity) are interrogated by a CR23X datalogger. Calculation of mean statistics and "on-line" estimates of sensible heat flux and u* are performed by the CR23X and stored in the logger's data buffer. These CR23X stations are periodically called by a telecommunication program from a Windows NT workstation in the tower lab building. Both 10Hz sonic data and the mean statistics are downloaded via a T1 line and written onto a magneto-optical disk (MO, 4.6 GB capacity). Ambient air is admitted to a teflon tube through an intake funnel close to the sonic anemometer array, to allow eddy correlation. It subsequently passes through a filter and is pumped through a LICOR-6262 IRGA inside the tower lab. All IRGAs are located inside the climatized lab building and are interrogated for CO2, water vapor, cell-pressure and cell-temperature by a CR23X. The lag in the IRGA data collection is accounted for by the post-processing program, using the standard method of correlation optimization, following (e.g.) Leuning and Judd (1996)
Both the raw eddy correlation data and the mean statistics are routinely stored on MO discs and transferred to Indiana University, where postprocessing and analysis occur.