PhD Defense: Gergely Dolgos

TITLE: Polarized Imaging Nephelometer Development and Applications on Aircraft ABSTRACT: Satellite remote sensing is the only method that is able to measure climate forcing atmospheric constituents on a global scale. Aerosols have large impacts on climate, through influencing radiation directly and through their effects on clouds. Remote sensing algorithms that deduce aerosol properties from satellite measurements of scattered sunlight rely on information about scattering patterns of aerosols. Chapter 1 of the dissertation places the work in context through a literature survey, and introduces and clarifies theoretical constructs necessary for understanding the rest of the work. In order to improve our understanding of light scattering by aerosol particles, and to enable routine in situ airborne measurements of aerosol light scattering to calibrate and validate satellite algorithms, at LACO (Laboratory for Aerosols Clouds and Optics) we have developed an instrument called the Polarized Imaging Nephelometer (PI-Neph). We designed and built the portable PI-Neph instrument at UMBC (University of Maryland, Baltimore County); it directly measures the ambient volume scattering coefficient and the phase matrix elements P11, phase function, and –P12/P11, polarized phase function. Chapter 2 introduces the PI-Neph instrument, while chapter 3 lays out the calibration and data reduction algorithm. The PI-Neph employs illuminating lasers and polarization control, sampling of ambient air through an inlet, and wide field of view detection of scattered light in a scattering angle range of 3° to 176°. The instrument does not employ any moving parts, therefore it is robust and fast enough for airborne measurements. The PI-Neph first measured at a laser wavelength of 532nm, and was first deployed successfully in 2011 aboard the B200 aircraft of NASA Langley during the DEVOTE (Development and Evaluation of satellite ValidatiOn Tools by Experiments) project. In 2013, we upgraded the PI-Neph to measure at 473nm, 532nm, and 671nm nearly simultaneously. LACO has deployed the PI-Neph on a number of airborne field campaigns aboard three different NASA aircraft. This dissertation describes the PI-Neph instrument, the measurement approach, algorithm, and calibrations. Chapter 4 is a validation and error analysis case study, which quantifies the agreement of artificial polystyrene sphere data with Mie theory. The validation data was collected during the 2012 deployment for the Deep Convective Clouds and Chemistry (DC3) field campaign. Chapter 4 quantifies the P11 and –P12/P11 calibration errors through a Monte Carlo simulation. Chapter 5 presents highlights from field measurements. The DEVOTE project enabled the initial PI-Neph results, such as scattering coefficient validation via comparison to other measurements, comparison of polystyrene sphere data to Mie theory, a comparison to AERONET derived phase function, and retrieval of microphysical properties of aerosols in collaboration with Dr. Oleg Dubovik. Chapter 5 also provides an overview of DC3 data, an assessment of data quality, and quantifications of PI-Neph capabilities and noise levels.