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Description
The Aerosol Limb Imager (ALI) is a multi-spectral polarimetric imager designed to observe scattered sun light in the limb. ALI collects images in a narrow spectral band in one of two orthogonal polarization states for the purpose of retrieving aerosol number density and particle size information within the upper-troposphere lower-stratosphere. Of novelty is the polarimetric nature of the aerosol observations. The two orthogonal polarization states are used to detect cloud in the spectral data and facilitate its distinction from aerosol.
To obtain an image at a desired wavelength and polarization state, ALI employs a system of linear polarizers, a liquid crystal rotator, and an acoustic-optic tunable filter. These components use no moving parts and provide the capability of imaging in the two polarizations at a select wavelength between 500 nm and 1500 nm.
To date, multiple iterations of the ALI instrument concept have been demonstrated on stratospheric balloon platforms. The current version of ALI has been successfully deployed on two separate stratospheric balloon launches: 2021 in Kiruna, Sweden and 2022 in Timmins, Ontario. From the geometry afforded by a stratospheric balloon, ALI can provide a spectral sample in increments of <100 meters and produces useful aerosol observations between 9 km and 30 km in altitude.
