PhD Thesis, 2007 - University College Cork

Chapter 3
Materials and Methods
2) The CO 2 and LE fluxes were corrected for variation in air density (Webb et
al., 1980), while H was corrected for moist air (Shotanus et al., 1983).
The post processing filters excluded fluxes, if:
1) the 30 minutes fluxes were the result of the average of less than 95 % of
good 10 Hz data (thus if less than 10 Hz data passed the online filters for
that half hour); or if
2) the estimate of the vertical angle gave unrealistic outputs (typically in low
wind speed conditions); or if
3) less than 67 % of the flux footprint length (Hsieh et al., 2000) was
estimated to have originated from outside the pristine part of the bog; or if
4) the fluxes were measured during rainy periods or up to one hour after rain,
because of the poor performance of the open-path gas analyser in wet
conditions.
Moreover, CO 2 fluxes were excluded for realistic threshold values (Table 3.2).
The filter used were rather conservative and resulted in good CO 2 fluxes for the
daytime as being 56 % of total daytime fluxes in 2002/03, 67 % in 2003/04, 51
% in 2004/05 and 63 % in 2005/06. For the night, good CO 2 fluxes occurred
22 % in 2002/03, 26 % in 2003/04, 23 % in 2004/05 and 29 % in 2005/06.
LE were further rejected during the post processing, if:
a) the product between net radiation (R n ) and H gave a negative output; or if
b) LE was lower than –30 and higher than 280 W m -2 ;
c) winter LE were filtered for predetermined realistic threshold values for each
month (Table 3.1).
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