Generalized Aerosol Retrieval from Radiometer and Lidar Combined data / Generalized Retrieval of Aerosol and Surface Properties (GARRLiC/GRASP)

This document describes the GARRLiC (Generalized Aerosol Retrieval from Radiometer and Lidar Combined data) products as implemented in the ACTRIS/EARLINET framework. GARRLiC is a synergistic retrieval algorithm that combines sun/sky photometer measurements with elastic multi‑wavelength lidar profiles to derive a comprehensive set of aerosol optical and microphysical properties. The methodology retrieves key parameters such as aerosol size distribution, complex refractive index, particle sphericity, and vertically resolved aerosol concentration, while additional optical quantities (e.g., extinction, backscatter, single scattering albedo, and aerosol optical depth) are derived from these outputs. The document further details the data processing chain, product levels, and file structure, including NetCDF formats compliant with CF conventions, naming conventions, and metadata definitions. It also explains the integration of AERONET and ACTRIS/EARLINET lidar data, quality-controlled inputs from the ACTRIS Single Calculus Chain, and the availability and access of GARRLiC datasets through the ACTRIS ARES data infrastructure. Overall, this documentation provides the reference needed to understand, access, and use GARRLiC aerosol products, which deliver both column-integrated and vertically resolved information for atmospheric aerosol research.