The Aerosol Limb Imager: a hyperspectral, polarization imager for aerosol and cloud profiling in the UTLS

The Aerosol Limb Imager (ALI) is a remote sensing instrument concept for high vertical resolution profiling of aerosol extinction and cloud in the upper troposphere and lower stratosphere. Hyperspectral measurements of limb scattered sunlight radiance in the mid-visible and near infrared are achieved by using a large aperture imaging quality acousto-optic tunable filter with a dual transducer that is capable of tuning over the spectral range 500-1600 nm with 2-15 nm spectral resolution. The optical design also incorporates a liquid crystal polarization rotator that provides dual linear polarization measurement at several wavelengths with no moving parts. The combination of the wide spectral range and the polarization information in a non-linear inversion with a multiple scattering radiative transfer model allows for retrievals of aerosol extinction profiles, particle size distribution parameters, and cloud discrimination with a target vertical resolution of 250 m. The high-aspect ratio field-of-view provides cross track coverage for nearly global daily coverage from a polar, low earth orbit. Canada has proposed ALI as a contributed instrument to the NASA Decadal Survey satellite mission on Aerosol, Cloud, Convection and Precipitation (ACCP). An advanced prototype of the ALI instrument (referred to as version 2) has been developed and flown as a technology demonstration on stratospheric balloon in 2018. This talk will present the instrument concept, optical design, measurement simulations, and first results from the 2018 stratospheric balloon flight.