The Hyper-Angular Rainbow Polarimeter: Pre-Launch Calibration, Validation, and Advancements in Cloud Science
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Author/Creator ORCID
Date
2022-01-01
Type of Work
Department
Physics
Program
Physics, Atmospheric
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Distribution Rights granted to UMBC by the author.
This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
This item may be protected under Title 17 of the U.S. Copyright Law. It is made available by UMBC for non-commercial research and education. For permission to publish or reproduce, please see http://aok.lib.umbc.edu/specoll/repro.php or contact Special Collections at speccoll(at)umbc.edu
Abstract
Studying the climate requires comprehensive, accurate, and global measurements of the atmosphere and surface. Small, economical, and powerful platforms, like the Hyper-Angular Rainbow Polarimeter (HARP), are part of a new paradigm in Earth observation. HARP is a wide field-of-view imaging polarimeter that is uniquely ca-pable of sampling the Earth from 120 co-located views, four visible channels (440, 550, 670, and 870nm), and three distinct polarization states. The HARP instrument is low-cost (<$5 million), compact (10x10x30 cm), continues the heritage of earlier, successful space missions, while also expanding the information content possible in a single set of measurements. This dissertations connects the instrument science of the HARP mission to unprece-dented cloud property retrievals from HARP polarization data. A robust, physics-based calibration pipeline is developed for HARP and is shown to be accurate to 0.5% degree of linear polarization (DOLP) across all channels in the lab, a climate community requirement for modern aerosol and cloud retrievals. Calibrated meas-urements are compared to co-located data from the Research Scanning Polarimeter (RSP) during a field campaign in 2017 to validate the calibration across the entire HARP FOV. HARP and RSP agree within 1% in reflectance and DOLP over two de-sert and two ocean scenes, relative to their error models. These advancements also allow spatially resolved retrievals of liquid water cloud droplet size distributions (DSDs). The hyper-angular, wide swath measurement ena-bles spatial maps of cloud droplet effective radius (CDR) and variance (CDV) for HARP resolutions < 1 km from aircraft and < 10 km from space. This work shows that high resolution DSD retrievals are essential to understanding the correlation between reflectance, CDR and CDV, which have connections to cloud growth pro-cesses, and ultimately, radiative balance. With the upcoming launch of the NASA Plankton-Aerosols-Clouds-ocean Ecosys-tem (PACE) mission and the release of HARP CubeSat L1B data to the scientific community, the same calibration and cloud retrieval concepts discussed in this work may be used to help connect cloud microphysical properties to global radiative forc-ings. Current and future HARP datasets may provide strong rationale for including high-resolution, hyper-angle imaging polarimetry and small satellite technology on future major Earth science space missions.