According to the Licor 7500 manual, there is a 0.186 second sampling lag in the 7500. This can be increased with an output delay parameter, so that it can be synchronized with the sampling of a sonic. I've verified that the output delays on our 7500's are set to 0.
Since the CSAT3 and Licor operate asynchronously, I see no advantage in further adjustment of the Licor delay to be a multiple of the CSAT3 sample period.
We have not be been incorporating a 7500 lag in our data processing. We do correct for the 2 sample delay of the CSAT3 sonics. Subtracting 0.186 seconds from the 7500 samples does increase the correlation and fluxes between w and h2o and co2. The w'h2o' and w'co2' fluxes increase by about 15% when a lag of 0.186 is applied to the Licor data. These plots are of the corrected flux and the difference between the corrected and uncorrected fluxes, for 2 days, centered on Jul 18:
...
| Code Block |
|---|
dpar(start="2011 jul 17 17:00",lenmin=30,stns=1)
iod = prep(c("w.4.5m#1","h2o.4.5m#1","co2.4.5m#1"),rate=20)
x = readts(iod)
close(iod)
cwh = crosscorr(x[,1:2],lags=c(-1,1))>
plot(as.numeric(utime(positions(cwh))),cwh,xlab="lag(sec)",ylab="w.4.5m#1:co2.4.5m#1")
|