Abstract. The European Aerosol Research Lidar Network (EARLINET), part of the Aerosols, Clouds and Trace gases Research Infrastructure (ACTRIS), organized an intensive observational campaign in May 2020, with the objective of monitoring the atmospheric state over Europe during the COVID-19 lockdown and relaxation period. Besides the standard operational processing of the lidar data in EARLINET, for seven EARLINET sites having co-located sun-photometric observations in AERONET, a network exercise was held in order to derive profiles of the concentration and effective-column size distributions of the aerosols in the atmosphere, by applying the GRASP/GARRLiC inversion algorithm. The objective of this network exercise was to explore the possibility to identify the anthropogenic component and to monitor its spatial and temporal characteristics in the COVID-19 lockdown and relaxation period. While the number of cases are far from being statistically significant so as to provide a conclusive description of the atmospheric aerosols over Europe during this period, this network exercise was fundamental to derive a common methodology for applying GRASP/GARRLiC on a network of instruments with different characteristics. The limits of the approach are discussed, in particular the missing information close to the ground in the lidar measurements due to the instrument geometry, and the sensitivity of the GRASP/GARRLiC retrieval to the settings used, especially for cases with low AOD as the ones we show here. We found that this sensitivity is well-characterized in the GRASP/GARRLiC products, since it is included in their retrieval uncertainties.

<p>CALIGOLA (Cloud Aerosol Lidar for Global Scale Observations of the Ocean-Land-Atmosphere System) is a mission funded by the Italian Space Agency (ASI), aimed at the development of a space-borne Raman Lidar. A Phase A study to assess the technological feasibility of the laser source and receiver system is currently underway at the Leonardo S.p.A., while scientific studies in support of the mission are conducted by the University of Basilicata. Scientific and technical studies are furthermore supported by other Italian institutions (CNR-ISMAR, CNR-IMAA), with NASA also having expressed an interest in contributing to the mission .</p><p>Mission objectives include the observation of the Earth atmosphere, surface (ocean and land). Among the atmospheric objectives, the characterization of the global scale distribution of natural and anthropogenic aerosols, their radiative properties and interactions with clouds, and the measurements of ocean color, suspended particulate matter and marine chlorophyll.</p><p>The expected performance of CALIGOLA has been assessed based on the application of an end-to-end lidar simulator. Specifically, sensitivity studies have been carried out to define the technical specifications for the laser source, the telescope, the optics of transceiver, the detectors and the acquisition system. Simulations reveal that the system can measure Rotational Raman echoes from nitrogen and oxygen molecules stimulated at the three lengths wavelength of 355, 532 and 1064 nm. Simulations also reveal that elastic signals are strong enough to meet the requirements under different environmental conditions. As reference signal, several options have been considered. Among others, a temperature-insensitive rotational Raman signal including rotational lines from nitrogen and oxygen molecules.</p><p>A careful analysis of different potential orbits is ongoing, with the goal to identify solutions which maximize performance and scientific impact of both atmospheric and oceanic measurements. Near noon-midnight equatorial crossing times are preferable on the ocean side for diel vertical migration and phytoplankton observations, but degrade significantly the performances of atmospheric measurements due to the high solar background. For this reason is essential to find an orbit in which the solar contribution is low enough to obtain acceptable atmospheric results and at the same time the oceanic measurements are far enough from the night-day transitions for as many days a year as possible to assure correct interpretation of phytoplankton physiology. To counterbalance the degraded signal performances also lower obit height are considered, as well as the use of polarized filters to reduce the amount of solar radiation. The estimated performances under different conditions and considering different orbits will be showed during the presentation.</p>