Retrieval of aerosol properties using Polarized Imaging Nephelometer (PI-Neph) laboratory measurements and Hyper-Angular Rainbow Polarimeter (HARP) remote sensing observations

Abstract

Aerosols play an essential role in Earth's climate: they directly perturb Earth's radiation budget and indirectly modify cloud properties, influencing its energy and hydrological budgets. The direct radiative effects of aerosols, the absorption, and scattering of light, depends on the intrinsic optical properties of the particles, the total aerosol loading, and the radiative properties of the surface beneath the aerosol layer. Aerosols are highly variable in their spatial and temporal distributions and their optical and micro-physical properties; it is especially challenging to represent their radiative effect realistically in climate models. Therefore, aerosol radiative forcing remains one of the main uncertainties in global climate change estimation. To better characterize the aerosol role in the global radiation budget and narrow uncertainties in predicting climate change, we need to understand better and constrain these properties' temporal and spatial distributions. Even though we have multidecadal data of aerosol measurement using satellite instruments, to better constrain the aerosol forcing, we need to know more about the properties of aerosols and their effects on cloud formation. It is why less explored multi-angular polarimetric scattering measurements become important in aerosol measurements. Unlike single viewing imaging radiometer measurements, the multi-angular polarimetric measurements have better information on aerosol properties; the methodology in this thesis tries to use this information content to understand the aerosol properties better. Also, demonstrate the aerosol properties retrieval from the measurements made by a novel family of MAP instruments developed at the University of Maryland Baltimore County using an inversion algorithm called GRASP. The thesis includes results from the volcanic ash resuspension measurement using the PI-Neph (Chapter 3). Puthukkudy et al. (2020) made the first demonstration of aerosol retrievals from the AirHARP measurements during the NASA campaign ACEPOL 2017 (Chapter 4). In Chapter 5, the radiometric measurements made by the HARP CubeSat instrument using the prelaunch calibration are validated and tested using existing reference instruments. The results presented in this thesis using the multi-angular polarimetric scattering measurement helps in constraining the aerosol properties and thus reducing the aerosol forcing uncertainties and thus accurately predicting the climate response.