G2.02

G2.02     Lidar incomplete altitude coverage

Gap detailed description

Lidar profiling of atmospheric aerosol and cloud layers has become important for climate research during recent decades. Lidar systems have the technical limitation that they are limited in the coverage of the atmosphere close to the surface. The minimum distance beyond which the lidar can provide valid data depends on the particular configuration of the instrument and is in general different for each individual instrument from a series-produced model as it is dependent on the both the optical design of the instrument, as well as the alignment of optical elements.

The blind area close to the ground can pose a problem in the case that the atmospheric constituent is abundant in this domain and forms a substantial part of the total atmospheric column. Therefore, in cases where a lidar profile is being used to estimate a total column observation (for instance the aerosol extinction profile in relation to a satellite derived total aerosol optical thickness), considerable biases can occur.

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)

The use of a tailored configuration of multiple receiving telescopes, each optimised to cover a specific altitude range in the atmosphere is a possible approach to minimise the problem.

In the H2020 ACTRIS-2 project (2015-2019), expertise will be used to facilitate developments of easy to implement new optical configurations at EARLINET stations. The first and second reports of ACTRIS-2 (D2.5 and D2.7) related to technical upgrades and QA activities at EARLINET and Cloudnet stations, delivered in April 2016 and expected April 2017 respectively, will provide an update about the upgrades implemented.

Measurable outcome of success

A measure of success is the reduction of the minimum altitude reported for a given lidar station.

Achievable outcomes

Technological viability: medium.

Indicative cost estimate: medium (>1million).  If the technical implementation is limited to a single lidar channel the costs are modest per individual instrument. The number of channels that need to be involved in the expansion can be treated as a multiplicative factor. Also, no single instrument design is generally applicable, which adds another multiplicative factor to the design costs. 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 system available at the single EARLINET station.

Relevance

The issue is relevant for ground-based lidar-observed species with high abundance close to the surface, and will become more important as more ground based lidar observed ECVs will be used as reference observations.

Timebound

Ongoing

Gap risks to non-resolution