Integrating UAV-Based In-Situ and Ground-Based Remote Sensing Observations for Enhanced Aerosol Profiling

This study investigates the integration of Unmanned Aerial Vehicle (UAV)-based in-situ aerosol particle size distributions (PSD) with ground-based remote sensing techniques to estimate columnar particle size-distributions and vertically resolved aerosol concentrations. Observations of aerosol vertical distribution are essential for understanding their radiative impact on the atmosphere and interactions with clouds. Ground-based lidar-photometer setups are commonly employed to capture simultaneous information on both columnar and vertical aerosol physical and optical properties, providing complementary insights. For the retrieval of vertically resolved aerosol concentrations from aerosol extinction, one commonly employs an inversion parameter known as the effective radius and which is a product of the measured PSD.

Our study focuses on integrating Optical Particle Counters (OPCs, UCASS and POPS) and impactors for collecting high-altitude aerosol samples onto UAVs and conducting flights near co-located lidar and sunphotometers, utilizing the Unmanned Systems Research Laboratory (USRL; https://usrl.cyi.ac.cy) of The Cyprus Institute (CYI). Three diverse atmospheric campaigns in Cyprus, Cape Verde, and Greece are exploited for this purpose. These campaigns target different aerosol compositions and atmospheric conditions, providing a comprehensive dataset for evaluation. We aim to establish the link between the in-situ and remote sensing methods by exploiting scattering computations and retrieval algorithms.

Preliminary findings from the Fall Campaign in Cyprus reveal simultaneous observations from lidar,  sunphotometer and UAV in-situ optical particle counters during a dust episode. UAV-based PSDs demonstrate larger particle concentrations within the 1 to 10 μm range compared to AERONET retrievals. This feature is expected to influence the resulting concentrations computed from the lidar, because larger particles contribute the most to mass concentration and extinction, resulting in increased magnitudes for both parameters. This increase affects the effective radius, which (together with the density, the size- and shape- dependent scattering efficiency) is one of the conversion parameters between extinction and mass.

Overall, we seek to explore the synergy of UAV-based high-altitude in-situ observations with highly spatiotemporally resolved lidar profiles to enhance our understanding of observations of the  aerosol-intensive and extensive properties at different layers. This integration aims to understand and mitigate remote-sensing-only biases, address uncertainties, and characterize the reliance on assumptions.