Calculating ambient and cell statistics

At each relevant step of the raw data processing, statistics are calculated for all available variables, either sensitive or non-sensitive. Single-variable statistics include average, standard deviation, skewness, and kurtosis. Relevant covariances are also calculated, notably covariances among vertical wind component w and all other variables. In particular, covariances between w and ambient scalars such as gas concentrations or temperatures, used for flux estimates, are calculated after compensation of scalars time lags.

However, when a closed path instrument is used, other covariances might also be needed for correcting fluxes for the effect of air density fluctuations (Webb et al., 1980). Namely, for each given gas, the covariances w'c'h2o and w't'cell (where ch2o is water vapor concentration expressed in any suitable units) are needed, calculated after compensating ch2o and Tcell using the time lag of the gas under consideration. Here, of course EddyPro® Software checks that water vapor is measured by the same instrument that measures the concentration of the gas considered. Otherwise, the covariance w'c'h2o is not calculated.

If you wish to learn more about accounting for air density fluctuations in closed path systems, refer to Ibrom et al. (2007b), for example.