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Final calculations

Turbulent fluxes are calculated from covariances of the despiked and detrended
time series taking into account the delay time of signals determined during
the calibration procedure outlined in section . Periods
with incomplete sampling over the entire hourly period are not used for flux
calculation. Raw covariances are converted into physical quantities using equations
-.

To determine the quality of the measurement, and to classify the data Foken
and Wichura (1996) propose three tests: the instationarity test, the correlation
test and the integral turbulent characteristics test. In our case the instationarity
test of the hourly flux values is applied to qualify the data calculated. The
quality flags (e.g., the percentage of instationarity) can be used in the determination
of the net carbon balance of the region in such a way that flux values beyond
a specific threshold instationarity are not used, resulting in less random error
in the measurement. However, it should be noted that the effect of random error
in the determination of the net carbon budget of the region is not severe if
the time series available is long enough (Moncrieff et al., 1996).

Since the fluctuations of HO and CO measured by the LI-COR
6262 are expressed in terms of mole fraction relative to dry air it is not necessary
to perform the corrections for variations of the density of air (Webb et al.,
1980; Grelle and Lindroth, 1996; Berger et al., 2001).

Additionally, Obukhov length is calculated from the turbulent characteristics
and stored to provide stability information neccessary for the spectral corrections
and for the flux source area analysis.

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2001-06-16