There are two types of data that are collected from each flux station involved in the AON project: high frequency eddy covariance (EC) data and low frequency means of meteorological and subsurface data.  On a daily basis, approximately 75Mb of high frequency binary data and 16Kb of low frequency ASCII data is collected.

This station uses a CR3000 datalogger and a laptop to collect and store data.  The CR3000 is used to measure the open-path EC equipment which is sampled at 10Hz.  Mircrometeorlogical data is scanned at 0.33Hz and all datapoints are averaged every half hour.  The CRBASIC program that controls the datalogger has been written in such a way that only the most basic corrections and filtering are applied to the raw data.  These would include shifting the CSAT3 and LI7500 data arrays by 2 and 3 scans respectively to account for the inherent processing delays of these sensors. 

About Data Processing

Time is expessed as local time, AST (UTC-9hrs) for Imnavait and MAGST (UTC+12hrs) for Pleistocene Park

Gas and energy fluxes are calculated from the high frequency time series using EdiRe or EddyPro software with these basic corrections:  despiking, coordinate rotation, spectral correction, the 'WPL' correction, and the 'Burba' correction (where appropriate, to account for instrument heating effects).

Some data have been filtered (_f) and gap-filled (_gf).

The generation of mass and energy fluxes from the high frequency data is performed with the following basic corrections:

The 'WPL' correction

A coordinate rotation

A spectral correction

The 'Burba' correction (where appropriate to account for instrument heating effect)

*Correct instrument lag adjustment occurs during datalogging

The following QA/QC variables are applied to the flux data:

Stationarity tests

Footprint analysis

Gas analyzer diagnostics are used as a QA/QC variable for both flux and radiation data

Rejection angles of 10° at Imnavait and 45° at Pleistocene Park are used when EC instruments were downwind of tower to remove flow distortions 

The flux and meteorological data is further post-processed to accomplish the following:

Data are within engineering specifications of each instrument. 

Removal of impossible measurements (e.g. negative precipitation)

Removal of outliers via a three-standard deviation filter

Removal of unrealistic changes in a time series with a step change filter

A similarity filter to remove errors from instruments that generate a string of identical values when not working

Flux variables are calculated using Licor's EddyPro flux processing software. The quality control flags for flux variables (either raw or filtered) are calculated using the Mauder and Foken (2004) method within the EddyPro. Flag values and meanings are available on the Licor web site at https://www.licor.com/env/help/eddypro/topics_eddypro/Flux_Quality_Flags...

Gaps in the data are filled using the BGC_Jena gapfilling tool ReddyProc.  Information on the gap-filling protocol is available here, https://www.bgc-jena.mpg.de/bgi/index.php/Services/REddyProcWebGapFilling. The meaning of the quality control flags for all gap-filled (_gf) variables is listed here (https://www.bgc-jena.mpg.de/bgi/index.php/Services/REddyProcWebOutput) under the _fqc entry.

 
See the file  2014_IC_1993_metadata_20141231.csv for data collection statistics.