Water vapour is an essential climate variable involved in many processes, widely determining the energy budget of our planet. The profiling of the atmospheric relative humidity is therefore part of the parameters to be measured in the framework of the European Research Infrastructure ACTRIS.
More and more French lidars have the ability to measure water vapour in the atmosphere using the Raman effect on water vapour and nitrogen molecules : OHP (Haute-Provence), OPAR (La Réunion), SIRTA (Paris), COPDD (Clermont-Ferrand), LOA (Lille). Water vapor concentration is calculated using the ratio of the H2O and N2 backscattered Raman signals with a correction of the atmospheric absorption [1, 2, 3, 4]. While the processing itself is relatively straightforward, there are two main difficulties for its automation: pre-processing and calibration. Indeed, these two points are highly dependent on the system design and the used calibration scheme [2, 3].
An automatic and near real time processing chain is now available and data are routinely produced at the AERIS/ESPRI atmospheric data centre for OPAR and COPDD ground stations. For the time being, only uncalibrated data are available in ASCII format.
The development of the algorithm has been initialized by Christophe Hoareau, Davide Dionisi and Philippe Keckhut (LATMOS), and completed by Hélène Vérèmes (LACy) and Guillaume Payen (OSU Réunion). It continues with the ACTRIS-Fr water vapor lidar group composed of PIs and engineers of involved observatories, software developers (Guillaume Payen and Franck Gabarrot, OSU-Réunion), and supported by AERIS for data production and data formating (Renaud Bodichon, AERIS/ESPRI) and Fabienne Lohou (LA) for group organization.
Next work roadmap tasks are: include calibration into the processing chain, data formating for NDACC compliance, optimize software configuration for the remaining ground stations (OHP, SIRTA, LOA).
This work benefits the wide ACTRIS-Fr community and fits into the national efforts to meet the ACTRIS requirements.
 Hélène Vérèmes, Guillaume Payen, Philippe Keckhut, Valentin Duflot, Jean-Luc Baray, et al.. Two-year operation of the lidar 1200: from fine-scale tropospheric structures to lower stratospheric water vapor detection. EPJ Web of Conferences, EDP Sciences, 2018, The 28th International Laser Radar Conference (ILRC 28), Bucharest 2017, 176, pp.05015. ⟨10.1051/epjconf/201817605015⟩. ⟨insu-01569600⟩
 Hélène Vérèmes, Guillaume Payen, Philippe Keckhut, Valentin Duflot, Jean-Luc Baray, et al.. Validation of the Water Vapor Profiles of the Raman Lidar at the Maïdo Observatory (Reunion Island) Calibrated with Global Navigation Satellite System Integrated Water Vapor. Atmosphere, MDPI 2019, 10, pp.713. ⟨10.3390/atmos10110713⟩. ⟨insu-02373121⟩
 Davide Dionisi, Philippe Keckhut, Yann Courcoux, Alain Hauchecorne, Jacques Porteneuve, et al.. Water vapor observations up to the lower stratosphere through the Raman lidar during the Maïdo LIdar Calibration Campaign. Atmospheric Measurement Techniques, European Geosciences Union, 2015, 8, pp.1425-1445. ⟨10.5194/amt-8-1425-2015⟩. ⟨hal-01073965⟩
 Christophe Hoareau, Philippe Keckhut, Jean-Luc Baray, Laurent Robert, Yann Courcoux, et al.. A Raman lidar at La Reunion (20.8° S, 55.5° E) for monitoring water vapor and cirrus distributions in the subtropical upper troposphere: preliminary analyses and description of a future system. Atmospheric Measurement Techniques, European Geosciences Union, 2012, 5 (6), pp.1333-1348. ⟨10.5194/amt-5-1333-2012⟩. ⟨hal-00635877⟩