Improved methods of cloud characterization from satellite measurements of horizontal atmospheric transmissivity

Chuntao Liu, University of Wyoming

PhD Defense

The satellite borne Stratospheric Aerosol and Gas Experiment (SAGE) instrument measures the attenuation of solar radiation through the atmosphere limb at sunrise and sunset events. These measurements contain information about the gases, aerosols and clouds responsible for the observed attenuation at different wavelengths in the visible to near-infrared range. This work focuses on the methods to extract cloud information from the measurements.

Three approaches are discussed using SAGE II measurements. The first approach identifies occurrences of clouds by comparing retrieved atmospheric extinction at two wavelengths. Applying the method to 17 years of data, the global and temporal distributions of upper tropospheric clouds and stratospheric volcanic aerosols are obtained and compared to former studies. The second approach taken was to simulate SAGE II transmittance data with a wide range of inputs to a forward model and generate a library of SAGE II transmittance data. The web-based library serves as a reference source for comparisons with observed events. The third approach is a direct inversion of cloud characteristics from observed transmittances. Case studies showed that the cloud fields so derived produced transmittance profiles that matched the observations. A limitation of the inversion method is that it requires a known set of ray traces, if such information is not available a priori, a series of approximations have to be used.