Cloud microphysical retrievals from hyper-angular wide FOV imaging polarimeter measurements

The Airborne Hyper-Angular Rainbow Polarimeter (AirHARP), designed and developed by the Laboratory for Aerosol and Cloud Optics (LACO) at the University of Maryland, Baltimore County (UMBC) is a wide field-of-view (FOV), hyper-angular imaging polarimeter for the microphysical sampling of clouds and aerosols from aircraft and space. This instrument performs comprehensive atmospheric measurements in both total radiance and polarization, at 4 VNIR wavelengths, and 120 unique viewing angles, all as a compact, low-cost, and easily scalable CubeSat payload. AirHARP is the airborne demonstration of the upcoming HARP CubeSat standalone instrument (2018, ISS orbit) and the HARP-2 polarimeter on-board the Plankton, Aerosol, Cloud ocean Ecosystem (PACE) satellite (2021, sun-synchronous polar orbit).

The AirHARP instrument observed clouds of various extent, depth, and phase in two NASA campaigns in 2017: the Lake Michigan Ozone Study (LMOS) and Aerosol Characterization by Polarimeter and Lidar (ACEPOL). This paper discusses the determination of cloud droplet effective radius and variance, two crucial parameters of the droplet size distribution, from AirHARP polarized cloud measurements from these campaigns, with associated error analysis.