10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Characterization of Phase Changes in Clouds Using Hyper-spectral LIF-LIDAR
OFIR SHOSHANIM, Adva Baratz, Israel Institute for Biological Research (IIBR)
Abstract Number: 1736 Working Group: Clouds and Climate
Abstract Cloud physics have great influence on global climate and Earth’s energy budgets, however their empirical research is of great challenge. The dynamics of the formation and disappearance of droplets is governed by a critical thermodynamic balancing between atmospheric composition and its micro-meteorology. When raindrops are formed under such conditions, while falling through the atmospheric boundary layer, a cleaning air might occur due to droplet-aerosol coalescence. Since research in situ is the only way to fully conserve the atmospheric condition and thermodynamics, the optimal way to interrogate such processes in the atmosphere is by remote sensing.
The research presented here makes use of a fluorescent amino-acid molecule (Tryptophan) as a nuclei-bio-marker to interrogate the phase of a cloud. Its spectral signature in dry- or wet- form, allows to follow the phase changes and dynamics of the cloud using laser induced fluorescence LIDAR (LIF-LIDAR)1. The sensitivity to the spectral shifts and the anisotropy of the material’s fluorescence is achieved in this work by exploiting the benefits of the hyper-spectral LIF-LIDAR which is based on an intensifier CCD (ICCD) sensor in a non-conventional way. We utilize this hyper-spectral LIF-LIDAR to measure the fluorescence spectra of aerosols (1-20 µm) from a distance of ~160 meters away. The back fluorescence from the aerosol phase is followed by UV photo-excitation (4th order of Nd+YAG laser-266 nm) and detected simultaneously for both VV & VH polarization components. We also develop a technique of photon counting, which has been implemented on a full chip-image, to reduce the noise to signal ratio in the ICCD readout. The experimental setup includes a 3 sqrm aerosol-cell which is instantaneously controlled and monitored, following the fluorescence anisotropy, the elastic depolarization backscatter, the peak pulse power (pre- and post-cell), the generation and size classification of the aerosol phase, and the ambient conditions inside the cell.
This study demonstrates gradual vanishing process of the spectral Stokes shift due to the drying process of the Tryptophan aerosol inside the cell. This drying is also responsible for the increase in the fluorescence anisotropy of the suspended Tryptophan molecules. The research shows that remote sensing with hyper-spectral detection allows tracking phase changes of aerosols in the atmosphere. Such LIF-LIDAR setup increases the spectral perceptivity of aerosol remote sensing and demonstrate a novel technique to the study of cloud dynamics.
[1] D. Joshi, D. Kumar, A. K. Maini, R. C. Sharma, Molecular and Biomolecular Spectroscopy 112, 446, 2013.