EARLINET QA programme

The European Aerosol Research Lidar Network, EARLINET, was founded in 2000 as a research project for establishing a quantitative, comprehensive, and statistically significant database for the horizontal, vertical, and temporal distribution of aerosols on a continental scale. Since then EARLINET has continued to provide the most extensive collection of ground-based data for the aerosol vertical distribution over Europe.

In the first 13 years of its existence, EARLINET has strongly increased its observing capacity. Currently, EARLINET is composed of 27 active stations. EARLINET measurements must meet stringent stability and absolute accuracy standards to achieve the desired confidence in aerosol radiative forcing needs; thus, the network has developed a rigorous quality assurance program addressing both instrument performance (Matthias et al., 2004; Freudenthaler et al., 2010) and evaluation of the algorithms (Böckmann et al., 2004; Pappalardo et al., 2004). These operational pillars have been developed to ensure instrument standardization and consistent lidar retrievals within the network in a standardized data exchange format.

As an overall calibration is not possible, methods and tools have been collected and developed to determine deviations on subsystem levels and to identify and assess the impact of critical subsystems by means of analytical methods. Freudenthaler et al. (2014) describes mandatory quality
checkups for each lidar system, some of which have to be performed regularly every year, some only once, in order to assess the performance and the temporal stability of a lidar system. One-time checkups are the test of the accuracy limits of the analog detection systems due to signal-induced distortions; they are carried out by means of a specialized electronic lidar test-pulse generator, developed within the framework of EARLINET, and the trigger-delay test, with which the accuracy of the zero-range for the range correction can be determined.