Level-0: Preliminary flux calculations
Results from preliminary flux calculations with relaxed processing settings assist in finding the most appropriate settings for final flux calculations (Level-1).
Level-0 flux results help to find the best settings for the final flux calculations. Generally, these preliminary results are used: - to check whether the flux processing works, - to check the wind direction across years, - to determine appropriate time windows for lag search for final flux calculations.
More details can be found in the documentation of the Flux Processing Chain
The Level-0 output of each EddyPro run is merged into one record per gas analyser before it is checked; the checks below all read that merged record.
OPENLAG runs to determine final lag ranges
The lag between turbulent departures of wind and the gas of interest was first determined in a relatively wide time window (called OPENLAG).
IRGA75 (2004-2017, 2019)
| time period | CO2 IRGA75 | H2O IRGA75 | Notes |
|---|---|---|---|
| 2004 | 0.20, 0.05-0.75 | same as CO2 | |
| 2005_1+4 | 0.25, 0.05-0.75 | same as CO2 | |
| 2005_2 | 0.20, 0.05-0.75 | same as CO2 | |
| 2005_3 | 0.20, 0.05-0.75 | same as CO2 | |
| 2006 | 0.20, 0.05-0.75 | same as CO2 | |
| 2007 | 0.20, 0.05-0.75 | same as CO2 | |
| 2008_1+4 | 0.20, 0.05-0.75 | same as CO2 | |
| 2008_2+3 | 0.25, 0.05-0.75 | 0.30, 0.05-0.75 | different lag for H2O |
| 2009 | 0.25, 0.05-0.75 | same as CO2 | |
| 2010 | 0.25, 0.05-0.75 | same as CO2 | |
| 2011 | 0.30, 0.05-0.75 | same as CO2 | |
| 2012 | 0.25, 0.05-0.75 | same as CO2 | |
| 2013 | 0.25, 0.05-0.75 | same as CO2 | |
| 2014 | 0.25, 0.05-0.75 | 0.30, 0.05-0.75 | different lag for H2O |
| 2015 | 0.25, 0.05-0.75 | same as CO2 | |
| 2016_1 | 0.25, 0.05-0.75 | same as CO2 | |
| 2016_2+3 | 0.30, 0.05-0.75 | 0.25, 0.05-0.75 | different lag for H2O |
| 2017_1+2 | 0.30, 0.05-0.75 | same as CO2 | |
| 2019_3 | 12.20, 11.90-12.70 | 12.15, 11.90-12.70 | artificial time lag added; different lag for H2O |
IRGA72 (2016-2025)
- IRGA72 OPENLAG time window size for initial lag search was from
-1sto+10sbetween 2016 and 2018, and from-1sto+20sfrom 2019 onwards. The later years required a wider time window because of the introduction of an artificial time lag of approx. 8s. The goal was to find an appropriate nominal time lag, and to determine a time window for lag search as narrow as possible. - The value
-1swas used as the starting value for the time window because EddyPro had issues with a start value of0s, in that case the lag search started e.g. at +1s for some reason (maybe bug) - The results from the OPENLAG runs were used to define a time window as narrow as possible for the final flux calculations (Level-1)
- The histograms of found OPENLAG time lags were inspected to determine whether there was a the histogram bin with peak distribution
- The peak of the distribution was used as nominal (default) lag, time ranges around this peak were used as time window (Table 2)
| time period | CO2 IRGA72 | H2O IRGA72 | Notes |
|---|---|---|---|
| 2016_2 | 0.35, 0.05-1.00 | 0.55, 0.05-4.00 | often faulty data |
| 2016_3 | 0.30, 0.05-1.00 | 0.40, 0.05-4.00 | |
| 2017_1+2 | 0.30, 0.05-1.00 | 0.45, 0.05-4.00 | |
| 2018_1 | 0.35, 0.05-1.00 | 0.45, 0.05-4.00 | |
| 2018_2 | 0.35, 0.05-1.00 | 0.40, 0.05-4.00 | |
| 2018_3 | only sonic | only sonic | low flow rate, no IRGA fluxes |
| 2018_4+2019_1 | 0.30, 0.05-1.00 | 0.45, 0.05-4.00 | |
| 2019_2 | n.a. | n.a. | IRGA data empty |
| 2019_4 | 8.40, 7.90-8.80 | 8.45, 8.00-13.00 | |
| 2020_1 | 8.40, 7.90-8.80 | 8.45, 7.75-13.05 | |
| 2021_1 | 8.40, 7.90-8.80 | 8.55, 8.00-13.00 | |
| (2021_2) | n.a. | n.a. | unknown data format |
| (2022_1) | n.a. | n.a. | unknown data format |
| 2022_2 | 1.25, 0.95-1.40 | 1.40, 1.00-4.00 | |
| 2022_3 | 8.95, 8.45-9.55 | 9.00, 8.20-13.05 | |
| 2022_4 | 8.45, 8.00-9.30 | 8.55, 8.00-13.00 | |
| 2023_1 | 8.45, 7.90-8.80 | 8.50, 7.75-13.05 | |
| 2023_2 | 8.45, 7.90-8.80 | 8.50, 7.75-13.05 | |
| 2024_1 | 8.45, 7.90-8.80 | 8.55, 7.75-13.05 | |
| 2025_1 | 8.45, 7.90-8.80 | 8.55, 7.75-13.05 | setup unchanged since 2023_2 |
Check wind direction across years
IRGA75 (2004-2017, 2019)
I compared histograms of wind directions between 2004 and 2017 and incl. the short time period in 2019 using Level-0 fluxes and found that a sonic orientation of 209° offset to north yields very similar results across years. It is therefore possible the the sonic orientation across all years was always close to 209°.
Here are results from a comparison of annual wind direction histograms (with bin width of 1°) to a reference period (2016-2017), all wind directions were calculated with a north offset of 209°, then a histogram was calculated for each year. The OFFSET describes how many degrees have to be added (or subtracted) to the half-hourly wind direction to yield a histogram that is most similar to the reference. All OFFSETS are small, which indicates that the wind directions are in good agreement (Table 3).
| YEAR | OFFSET |
|---|---|
| 2004 | 1 |
| 2005 | 1 |
| 2006 | 1 |
| 2007 | 1 |
| 2008 | 1 |
| 2009 | -1 |
| 2010 | 2 |
| 2011 | 1 |
| 2012 | 2 |
| 2013 | 3 |
| 2014 | 1 |
| 2015 | 0 |
| 2016 | 0 |
| 2017 | 0 |
| 2019 | 1 |
IRGA72 (2016-2025)
I compared histograms of wind directions between 2016 and 2025 using Level-0 fluxes and found that a sonic orientation of 209° offset to north yields very similar results across years. It is therefore possible the the sonic orientation across all years was always close to 209°.
Here are results from a comparison of annual wind direction histograms (with bin width of 1°) to a reference period (2024), all wind directions were calculated with a north offset of 209°, then a histogram was calculated for each year. The OFFSET describes how many degrees have to be added (or subtracted) to the half-hourly wind direction to yield a histogram that is most similar to the reference. All OFFSETS are small, which indicates that the wind directions are in good agreement (Table 4).
| YEAR | OFFSET |
|---|---|
| 2016 | -2 |
| 2017 | -3 |
| 2018 | 1 |
| 2019 | 0 |
| 2020 | 1 |
| 2021 | 1 |
| 2022 | 1 |
| 2023 | 2 |
| 2024 | 0 |
| 2025 | 1 |