Campbell Scientific Open Path Eddy Covariance (OPEC) - Manual (Page 32)

OPEC Open-Path Eddy-Covariance System
4.2 Data Processing
There are several ways to process the raw time series data collected by the
system. Some of these are considered standard by the community and others
are subject to much debate. To gain a better understanding of the issues,
review the literature.
4.2.1 Online Processing
The Open-Path Eddy-Covariance datalogger programs perform the processing
listed below online and in real time. In many cases, no further processing of
the data is required.
• Thirty minute statistics for the turbulence and meteorological
variables, these include fluxes, means, and standard deviations. The
output period can be changed by changing the Constant
OUTPUT_PERIOD.
• Compute the mean moist air density, temperature, and vapor pressure.
Air density is used to compute the sensible heat and momentum flux.
• Webb et al. (1980) term for latent heat flux and CO
2
flux. This term is
separated into its two components, e.g., one term for temperature and
the other for vapor density.
• Wind direction and wind speed from the sonic anemometer.
• Compute the KH20 Krypton Hygrometer oxygen correction.
• Cross-products (second moments) required for an off-line coordinate
rotation following Kaimal and Finnigan (1994) and Tanner and
Thurtell (1969).
The datalogger programs do not apply a coordinate rotation to
the data. NOTE
4.2.2 Off-line Processing with EdiRe
EdiRe is a powerful and flexible software package for processing Eddy-
Covariance data collected by a Campbell Scientific system. It is available at no
charge from the University of Edinburgh’s ftp site (http://www.geos.ed.ac.uk/
abs/research/micromet/EdiRe/Downloads.html). EdiRe can, using the
Interpreter, read TOB1 data files. EdiRe will sort the input data files by date
and time, and can deal with files that are not the same size, e.g., collected using
two cards.
Some of the available EdiRe processing functions are:
• Statistics for the turbulence and meteorological variables, these
include means, standard deviations, and covariances.
• Filtering the data (detrending, recursive, FIR, exponential).
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