What can limb scatter tell us about aerosols?

Abstract

Profiles of light scattered from the limb of the terrestrial atmosphere can provide information upon the vertical structure of optically thin aerosol layers. Such data can also be used to determine the upper altitude of thicker layers (/spl tau/>0.01). Multi-wavelength measurements can help determine relative size distribution, but only with assumptions concerning the particle index of refraction and shape. Measurements of polarization can help to narrow the range of possible optical constants and shapes, but the small range of scatterings angles limits the degree of useful information. Despite these limitations, limb scatter observations can be quite useful for stratospheric aerosol research and examining the injection of aerosols into the upper troposphere and lower stratosphere. Presented is an algorithm for the estimation of the aerosol extinction profile from 10-30 km using limb scatter radiance profiles. Data is presented from the 1 am channel of the Limb Ozone Retrieval Experiment (LORE) flown on-board STS107 (Columbia). Comparisons are made with aerosol extinction profiles measured by the Stratospheric Aerosol and Gas Experiment (SAGE) II using the solar occultation method. On average the difference for the LORE data is less than 20% with a variation of 40%. Additional results are presented for multi-wavelength Limb scatter observations made by SAGE III. Analysis of the retrievals shows altitude registration and stray light to be the major error factors.