Level 1. Logger specific raw data are periodically downloaded over a physical link to a PC located at the GAW station and transmitted via internet to WORCC where they are archived as monthly files.
Level 2. Daily files of quality controlled measurements including station and instrument-specific meta data. Quality control covers instrument status, solar pointing accuracy and cloud screening. Level 2 files are the basic data units suitable for self-consistent evaluation of AOD results or Langley calibration runs. Level-2 files are produced by standardised software that issues diagnostic messages as a result of quality control.
Level 3. Daily files of AOD results including summary data in meta header are produced on a monthly basis at WORCC. Additional quality control is performed manually on monthly results in order to detect unusual situations and to resolve or clarify them in collaboration with station operators.
Quality Assured hourly AOD available as a yearly file including basic statistics. Quality assurance covers a posteriori calibration of the PFR instrument and reprocessing of Level 3 data using linear interpolation of calibration when required, as well as manual inspection of potential outliers identified by statistical analysis.