G2.04     Missing continued intercomparison with reference systems

Gap detailed description

Lidar profiling of atmospheric aerosol has become important for climate research during recent decades. Lidar systems cannot be independently calibrated. Therefore, the accuracy of aerosol lidar measurements can only be assured with internal instrumental quality checks, consistency of lidar observations with other instruments (e.g. total column aerosol observations), and through intercomparisons with lidar systems with a very well known and well documented behaviour – so called reference systems. Since reference systems are scarce (because they are expensive due to the need for experienced crew and documentation of the system) and intercomparisons have to be done by collocating the reference systems with one or more lidar systems under test, which is a very time consuming and costly procedure. Ideally, intercomparisons with reference lidar systems should be done regularly, but time and funding are insufficient to make this happen.

Activities within GAIA-CLIM related to this gap

This gap will not be addressed within GAIA-CLIM. However, ongoing activities in other projects will be monitored and reported on.

Gap remedy(s)

Internal quality checks and consistency with other observations must be made mandatory for established ground based aerosol lidar stations, as is done for ACTRIS/EARLINET in Europe and other networks (e.g. LALINET in South America). Furthermore, efforts should be put into sourcing funding for more regular intercomparisons with reference lidar systems. The overall recommendation is that each established ground based aerosol lidar station should be inter-compared with a reference lidar at least once during the early phases of operation of the ground based aerosol lidar station.

Measurable outcome of success

Number of inter-comparisons of ground based aerosol lidars with reference systems.

Achievable outcomes

Organizational viability: low.

Indicative cost estimate: medium (>1million).  Need for experienced crew, reference lidar systems, transportation, travel costs, and campaign and analysis time.


The issue is highly relevant for any application that uses ground based aerosol lidar data as a reference.



Gap risks to non-resolution


Identified future risk / impact

Probability of occurrence if gap not remedied

Downstream impacts on ability to deliver high quality services to science / industry / society

Missing continued intercomparison with reference systems


Reduced level of traceability of ground based aerosol lidar measurements.





Work package: