CH-MULTI / FF-202008
Flux calculations for CH-AWS 2020 (new), CH-DAV 2015 (updated), CH-DAV 2020 (new), CH-FRU 2017 (updated) CH-FRU 2020 (new), CH-LAE 2020 (new), CH-OE2 (new)
Flux calculations for CH-AWS 2020 (new), CH-DAV 2015 (updated), CH-DAV 2020 (new), CH-FRU 2017 (updated) CH-FRU 2020 (new), CH-LAE 2020 (new), CH-OE2 (new).
- Calculated fluxes for IRGA72 and IRGA75: CO2 and H2O
- CH-FRU 2017 IRGA75 fluxes were re-calculated because of the Wrong Calibration Gas 2017.
- CH-DAV 2015 IRGA72 fluxes were calculated to replace the IRGA75 fluxes shared so far in FLUXNET with IRGA72 fluxes.
- All 2020 fluxes are new and include data until incl. 30 June 2020.
- Python script for conversion to CSV and flux calculations: FCT v0.9.6
- With this FCT version, the calibration gas issue can be corrected during the conversion of the EC raw data files from binary to CSV, before they are used in flux calculations.
- EddyPro version: 7.0.6 (18 Dec 2019)
Calibration Gas Issue
- See here for more details on this issue.
- In this patch, only CH-FRU 2017 was affected by this issue (complete year).
- The calibration gas used to calibrate IRGA CO2 measurements during CH-FRU 2017 was wrong and the CO2 measurements needed to be corrected before flux calculations. This correction cannot be done in EddyPro directly. High-res CO2 raw data of these time periods were multiplied by a factor of 0.974 during the conversion from the raw binary format to the CSV format.
Open Lag Runs
The lag time between SA and IRGA was checked 2017 – 2020 in time windows of 0-10s. This was done by searching the max covariance without using a default lag time in EddyPro, i.e. all found lag times in the EddyPro full_output file show found lag times. The peak of the distribution of all found lag times per year were:
- CH-AWS 2020: OPENLAG search in time window 0-10s, lag distribution peaks: CO2@1.30s, H2O@1.40s
- CH-DAV 2020: OPENLAG 0-10s, lag distribution peaks: CO2@1.25s, H2O@1.30s
- CH-FRU 2020: OPENLAG search in time window 0-10s, lag distribution peaks: CO2@0.15s, H2O@0.15s, narrow final search window 0-5s
- CH-LAE 2020: OPENLAG search in time window 7-20s, lag distribution peaks: CO2@8.40s, H2O@8.45s, final search window 5-12s
- CH-OE2 2020: OPENLAG search in time window 0-10s, lag distribution peaks:
- CO2@1.30s, final search window 0-5s (found lags are very narrow)
- H2O@1.40s, final search window 0-10s (lag is quite dynamic)
- CH-FRU 2017: OPENLAG search in time window 0-10s, lag distribution peaks: CO2@0.15s, H2O@0.15s, no clear unique peak, using the same settings as CH-FRU 2020: final search window 0-5s
- CH-DAV 2015: OPENLAG search in time window 0-10s, lag distribution peaks: CO2@0.50s, H2O@0.85s, final search window 0-10s
Off-season Carbon Uptake Correction (Burba Correction)
- No correction for the IRGA75 at CH-FRU 2017 was applied, since the true correction factor is currently unknown. The implementation of this correction in EddyPro most likely over-corrects CH-FRU fluxes and was since not applied during flux calculations.
- Quality control with Python script FQC v2.1.2.
- AGC QC was not used since our logging system stops recording data if weather gets too bad (i.e. bad signal). In previous years, AGC QC was still applied in some form, so this is a difference to previous final flux runs.
- QC settings are shown here: