Unmanned Aerial Vehicles for satellite calibration and validation

A large amount of development has occurred in the last few years around the launch of two spaceborne lidar missions by the European Space Agency (ESA). Aeolus, active from 2018 to 2023, was the first satellite capable of observing winds from the surface to the stratosphere, and has led to significant progress in atmospheric dynamics research and operational weather forecasting. EarthCARE, expected to be launched in the first half of 2024, aims to significantly improve our understanding of how clouds and aerosols affect the Earth radiative budget, with observations at unprecedented levels of accuracy. The Cyprus Institute (CyI) contributes to the calibration and validation of both satellites. During June 2022, the Unmanned Systems Research Laboratory (USRL), an ACTRIS national facility and mobile exploratory platform, took part in the ESA-ASKOS experiment in Mindelo, Cape Verde, and operated several Unmanned Aerial Vehicles (UAVs), fitted with a number of unique in-situ aerosol instruments able to profile the Saharan Air Layer between the surface and an altitude as high as 5,300 m ASL. The campaign aimed to validate the Aeolus L2A product in the presence of dust and marine aerosols, estimate the influence on Aeolus products of non-spherical particles, evaluate the impact of particle orientation, and study the diurnal cycle of the dust size-distribution at high altitudes. The instruments deployed on-board the UAVs permitted evaluation of the vertically-resolved particle size-distribution between 0.1 and 40 m diameter and complementing observations of ground-based remote sensing set out by NOA and TROPOS. Moreover, high-altitude dust samples were collected on impactors, for further analysis by Scanning Electron Microscopy. The airborne in-situ particle size-distributions and the lidar remote sensing observations show a similar atmospheric structure and comparable estimates of the aerosol concentrations. Moreover, the collected high-altitude samples are able to inform on the size-resolved particle mineralogy, dominated by clay and silicates in this campaign. Similar experiments, to be held in Cyprus within the framework of the CORAL and ATMO-ACCESS pilot projects, will permit to evaluate the EarthCARE aerosol products. In addition to USRL, the Cyprus Institute operates the Cyprus Atmospheric Observatory (CAO), which provides long-term in-situ and remote sensing observations over the island, and which is another valuable validation infrastructure, and also an ACTRIS national facility. Moreover, a great potential for the exploitation of synergies is available through the collaboration and memorandum of understanding with the nearby ERATOSTHENES centre of excellence, home of another national facility, the Cyprus Atmospheric Remote Sensing Observatory (CARO). In this presentation we will discuss the potential and complementarity of in-situ UAV observations with ground-based remote sensing for the cal/val of Aeolus and EarthCARE, the knowledge acquired during the ASKOS campaign in Cape Verde, the opportunities stemming from the strategic location of Cyprus for the cal/val of EarthCARE, the existing plans, the room for further development, the funding opportunities, and the challenges.