PhD Proposal: Anin Puthukkudy
TITLE: Towards an Ideal Database for Microphysical and Optical Properties of Volcanic Ash
ABSTRACT: Volcanic ash has the potential to cause a variety of severe problems for human health and aviation safety, and can alter the Earth’s radiative transfer budget locally. Therefore, effective monitoring of the dispersion and fallout from volcanic ash clouds and characterization of the aerosol particle properties is essential. One way to acquire information from volcanic clouds is through satellite remote sensing; such images have greater coverage than ground-based observations and can present a “big picture” perspective. A challenge of remote sensing is that assumptions of certain properties of the target are often a pre-requisite for making accurate and quantitative retrievals. For example, detailed information about size distribution, sphericity, and optical properties of the constituent matter is needed, otherwise it must be assumed. The same kind of information is also needed for atmospheric transport models to properly simulate the dispersion and fallout of volcanic ash. Proposed here is a laboratory method to determine the microphysical and optical properties of volcanic ash samples collected from volcanoes with markedly different compositions. Proposed research uses a Polarized Imaging Nephelometer (PI-Neph) and a system that re-suspends the particles in an air flow. The PI-Neph measures angular light scattering and polarization of the re-suspended particles from 3o to 175o scattering angle, with an angular resolution of 1o. Primary measurements include phase function and polarized phase function at three wavelengths (445nm, 532nm, and 661nm). Size distribution, sphericity, and complex refractive index are retrieved indirectly from the PI-Neph measurements using the GRASP (Generalized Retrieval of Aerosol and Surface Properties) inversion algorithm. We also report the results of this method applied to samples from the Mt. Okmok (2008) and Mt. Katmai (1912) volcanic eruptions. The goal of this proposed research is to provide a database with microphysical and optical properties of different volcanic ash, which can be used for the remote sensing/ash dispersion model calculations.