Synergic Retrieval of Atmospheric Aerosol Properties Using Visible and Thermal Infrared Spectrum.

In this work, we suggest synergy of visible (VIS) and thermal infrared (TIR) spectrum for enhanced retrieval of aerosol composition information. Sensitivity of spectral extinction and directional scattering in VIS to aerosol size, shape and refractive index is widely employed for aerosol properties retrievals. Despite the lack of directional scattering information in the long wave radiation, which limits the retrievals restricted to the TIR only, several minerals contained in desert dust present highly distinguishable spectral variability of complex refractive index. Additionally, longer wavelengths can improve sensitivity to aerosol sizes. The combination of both spectral ranges is therefore expected to improve aerosol characterization in general and aerosol components retrievals in particular. The high capabilities of GRASP (Generalized Retrieval of Atmosphere and Surface Properties) algorithm (Dubovik et al., 2014) to retrieve aerosol and surface properties from space-borne and ground-based remote sensing observations in VIS and near infrared (NIR) spectral ranges has been widely proven in diverse applications (Torres et al., 2016; Chen et al., 2020, Lopatin et al., 2021). Li et al. (2019) demonstrated GRASP/components retrieval methodology which enables distinguishing different aerosol components from observations in VIS and NIR spectra. We integrate now the TIR radiative transfer into the GRASP code, update the retrieval strategy and, additionally to the previously available aerosol chemical components, we evaluate the fractions of quartz and clays in the desert dust aerosol. The combined observations by AERONET (Aerosol Robotic NETwork) (Holben et al., 2018) sunphotometer and TIR radiometer (Legrand et al., 1999; Brogniez et al., 2003) are employed to demonstrate the retrievals.