The Aerosol Limb Imager: acousto-optic imaging of limb-scattered sunlight for stratospheric aerosol profiling

Abstract

Abstract. The Aerosol Limb Imager (ALI) is an optical remote sensing instrument designed to image scattered sunlight from the atmospheric limb. These measurements are used to retrieve spatially resolved information of the stratospheric aerosol distribution, including spectral extinction coefficient and particle size. Here we present the design, development and test results of an ALI prototype instrument. The longterm goal of this work is the eventual realization of ALI on a satellite platform in low earth orbit, where it can provide high spatial resolution observations, both in the vertical and cross-track. The instrument design uses a large-aperture acousto-optic tunable filter (AOTF) to image the sunlit stratospheric limb in a selectable narrow wavelength band ranging from the visible to the near infrared. The ALI prototype was tested on a stratospheric balloon flight from the Canadian Space Agency (CSA) launch facility in Timmins, Canada, in September 2014. Preliminary analysis of the hyperspectral images indicates that the radiance measurements are of high quality, and we have used these to retrieve vertical profiles of stratospheric aerosol extinction coefficient from 650 to 1000 nm, along with one moment of the particle size distribution. Those preliminary results are promising and development of a satellite prototype of ALI within the Canadian Space Agency is ongoing.

A novel, balloon-borne UV/visible spectrometer for direct sun measurements of stratospheric bromine

“…Measurements during the ascent of the balloon into the stratosphere were impossible due to both technical problems with our instrument and difficulties with the azimuth-stabilisation of the gondola. GLORIA and ALI (Aerosol Limb Imager by the Institute of Space and Atmospheric Studies at the University of Saskatchewan, Elash et al (2016)) were other scientific payloads on the same flight. While we report on the performance of the solar tracker for the first flight, spectroscopic artefacts (etalon structures) hinder us from carrying out and reporting on the spectral analysis.…”

Systematic comparison of vectorial spherical radiative transfer models in limb scattering geometry

“…In spherical mode, MYS-TIC uses the backward MC method. MYSTIC contains specialized variance reduction methods for handling strongly peaked phase functions (Buras and Mayer, 2011) and is capable of handling atmospheres where the parameters vary in three dimensions (not just in altitude) (Emde and Mayer, 2007;Emde et al, 2017). High-spectral-resolution radiances can be simulated efficiently using the ALIS (Absorption Lines Importance Sampling) method (Emde et al, 2011).…”