G2.01    24/7 operation of aerosol lidar

Gap detailed description

Lidar profiling of atmospheric aerosol and cloud layers has become increasingly important for climate research during recent decades. More recently, the aircraft safety strategies followed after the volcanic eruption hazards of Eyjafjallajökull and Grimsvötn (Pappalardo et al., 2014) have increased the need for height-resolved monitoring of the aerosol concentration on continental scales.

Most of the lidar measurements are not performed continuously (i.e. 24 hours/7 days a week). On the other hand, thousands of ceilometers and simple backscatter lidars are operating on a continuous basis all around the world though the quality of their contribution to the characterization of aerosol impact on weather and climate as well as to the satellite validation is limited compared to the more advanced multi-wavelength Raman lidar systems or HSRL, because of the strong assumptions needed to provide an estimate of the aerosol optical and microphysical properties. But, as a consequence of their complexity, higher-end lidar systems are quite expensive; thus their number is limited and many of them are operated by research institutes according to the local needs or to the protocols defined within research networks (e.g. EARLINET), or only occasionally during dedicated field campaigns. In principle, modern lidar instruments are capable of operating continuously, and several EARLINET stations can already provide continuous data. Continuous operation of aerosol lidars would dramatically increase the temporal coverage of lidar measurements for a continuous and sustained satellite validation program. Fully automated lidar systems would also decrease the high man-power costs involved in the operation of lidar systems, in particular during night-time measurements.  

Activities within GAIA-CLIM related to this gap

This gap will not be addressed within GAIA-CLIM. Rather, GAIA-CLIM activities carried out in the context of WP2, and addressed to define the full traceable uncertainty for the lidar optical properties, will support the activities planned in other projects, like ACTRIS and TOPROF, aiming at the near real-time delivery of 24h/7 days aerosol lidar products.

Gap remedy(s)

Remedy #1

Specific remedy proposed

In the context of the H2020 ACTRIS-2 project (2015-2019), the ACTRIS network expertise will be used to facilitate developments of easy to implement and robust solutions for automated operation and remote control of lidar instruments at EARLINET stations. The optimization of instruments for long-lasting or continuous (unattended) operation will increase the number of systems working 24h/7-day to increase the temporal coverage of lidar data. The first and second reports of ACTRIS-2 (D2.5 and D2.7 from that project) related to technical upgrades and QA activities at EARLINET and Cloudnet stations, delivered in April 2016 and expected in April 2017 respectively, will provide an update about the number of operational systems and an estimate of the timescale and cost required to make an advanced aerosol lidar operational at any other station. GAIA-CLIM activity carried out within WP2 to define the full traceable uncertainty for the lidar optical properties will be combined with ACTRIS efforts towards the near real-time delivery of 24h/7-day aerosol products. Efforts towards automation will increase the number of systems working 24h/7-day and therefore increase the coverage.

Measurable outcome of success

The implementation of the ACTRIS aerosol near-real time products, assured by the agreement between the systematic validation of aerosol near-real time products with the well-established EARLINET Raman lidar products. The use of these products by modellers and the satellite community, as well as their use to monitor special events, is expected but over a longer time scale.

Achievable outcomes

Technological / organizational viability: medium.  Technology has been already tested but its implementation in the existing system requires a significant effort.

Indicative cost estimate: high (>5 million)/ medium (>1million).  For an extended network lidar ACTRIS/EARLINET covering the European continent, it requires a medium/high investment. An exact estimation depends on the upgrades of the systems available at each candidate EARLINET station.


The ACTRIS/EARLINET work described above will allow to provide easy to implement and robust solutions for automated operation and remote control that will facilitate the optimization of instruments for long-lasting or unattended operation.


First outcome by end of ACTRIS project (2019).

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 continuous availability of lidar measurements for satellite validation


Aerosol products for the satellite cal/val will not ensure the appropriate coverage and may require the use of ground based lidars to assess satellite sensors’ performances.

Missing continuous monitoring especially of atmospheric events (dust storms, volcanic eruptions, others).


Society and economy are strongly impacted by natural hazards; a mitigation of this impact requires high resolution continuous measurements in time and space.


Work package: