Remote Sensing of Atmospheric Aerosols with the Aerosol Limb Imager

Stratospheric aerosol has a large impact on the atmosphere of the Earth. In particular, it cools the climate via scattering sunlight into space. Although many processes ensure both a natural and anthropogenic background presence of these aerosols, significant acute changes can occur with major events like volcanic eruptions. Their role in the climate of the Earth, as well as their variability makes continuous observation of stratospheric aerosol a significant scientific priority. The Aerosol Limb Imager (ALI) is an instrument concept developed by the University of Saskatchewan to contribute to this observation. It is a multi-spectral polarized imager and is designed to take images only of the Earth's illuminated atmosphere as a measure of the scatting sunlight. These measurements are then used to infer stratospheric aerosol. The novel concept of ALI is the polarimetric ability. No other existing scientific imager which makes this type of measurement has had the ability to measure polarization. Discussed within this work are efforts to advance the ALI scientific and engineering readiness to stratospheric aerosol observation. This not only involved constructing and demonstrating a new optical iteration of the ALI instrument concept, but also advancing the scientific analysis techniques which make use of the polarized information ALI produces. In pursuit of this, a new calibration technique was developed and published by this work concerning the polarimetric calibration of optical instrumentation. Advantages of this new technique include characterizing the full sixteen element Mueller matrix where a typical method may not, quantifies meaningful uncertainty, and gives indication to performance and alignment of specific optical components. This calibration technique facilitated the scientific analysis of ALI observations to quantify stratospheric aerosol. In particular the polarized information is used to robustly identify clouds which may otherwise be mistaken for aerosol by an analysis of this nature. In addition, the algorithm developed by this work also yields aerosol size information on top of the typical metrics that most other comparable instrumentation can report. These capabilities are demonstrated in practice with the analysis of ALI data taken during a high-altitude balloon flight in 2022, where agreement with three other space base instruments is established.