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CH-CHA / FF-202008

Flux calculations for years 2017 (updated), 2018 (updated), 2019 (new) and 2020 so far (new).

  • Calculated fluxes for IRGA75: CO2 and H2O
  • Fluxes 2017 were re-calculated because of the Wrong Calibration Gas 2017.
  • Fluxes 2018 were re-calculated because the years around it were newly calculated, to make the most recent years more homogeneous.
  • Fluxes 2019 are new
  • Fluxes 2020 are new and include data so far, until incl. 30 Jun 2020.

 

Level-1 Fluxes

  • 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)
  • For an overview of raw data formats see here.

 

Calibration Gas Issue

  • See here for more details on this issue.
  • The calibration gas used to calibrate IRGA CO2 measurements during the time period 2017_2 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.

 

Workflow

  1. All raw binary files were first converted to CSV format.
    • 2017_1 and 2017_3 were converted to CSV together, in the same run (FRMT D).
    • 2017_2 was converted separately (FRMT D-GN) because it is affected by the calibration gas issue and needed correction. The gain of 0.974 was applied to the two CO2 columns (CO2 in ppm and mmol) during their conversion from binary to CSV. This means that the CSV file format of these corrected files is the same (i.e. same columns and same order of columns) as for the other time periods.
    • 2018_1, 2018_2 and 2018_4 were converted together, in the same run (FRMT D).
    • 2018_3 was converted separately because there was a setup change for the QCL which changed the Byte sequence of the incoming data (see QCL-A3 in bico Data Blocks). This period could be pooled with the rest of 2018 for conversion if the focus is on IRGA fluxes, because the data block coming from the QCL is 22 Bytes for both QCL-A3 and QCL-A (but the order of the QCL columns changed in QCL-A3).
    • All 2019 time periods were converted in the same run (FRMT D).
    • All 2020 time periods were converted in the same run (FRMT D).
  2. Fluxes were then calculated:
    1. All 2017 fluxes in the same run.
    2. 2018_1 and 2018_2 in the same run.
    3. 2018_3 in a separate run, because the setup of the IRGA (position) has most likely changed.
    4. 2018_4 in a separate run, although this time period could be calculated together with 2018_3 if only the IRGA fluxes are of interest.
    5. All 2019 fluxes in the same run.
    6. All 2020 fluxes in the same run.

 

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:

  • 2017 – 2020: peak @0.25s for CO2, @0.30s for H2O
  • Since the distribution of found lag times was very narrow, the final lag search window was set to 0-5s for final flux calculations.

CH-CHA: Found lag times for CO2 and H2O in 2017-2020, lag search window 0-10s.

 

Spectral Correction

  • For the short time periods 2018_3 and 2018_4, the spectral assessment file from 2019 was used.

 

Off-season Carbon Uptake Correction (Burba Correction)

  • No correction was applied, since the true correction factor is currently unknown. The implementation of this correction in EddyPro most likely over-corrects CH-CHA fluxes and was since not applied during flux calculations.

 

Level-2 Fluxes

  • 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:

Last Updated on 18 Feb 2024 22:08