Title: Development and Application of Dual Photoelastic Modulator-Based Polarimetric Imaging Systems: GroundMSPI, AirMSPI, and AirMSPI-2
Presenting Author: Meredith Kupinski
Organization: University of Arizona
Co-Author(s): David J. Diner, Russell A. Chipman, Christine Bradley, Karlton Crabtree, Brian J.S. Daugherty, Ab Davis, Brian E. Rheingans, Veljko M. Jovanovic, Michael A. Bull, Gary Gutt, Bruce R. Hancock, Randall C. Hein, Michael E. Hoenk, Jason Kempenaar, Nasrat Raouf, Chris Wrigley, Sven Geier, Felix C. Seidel, Carol J. Bruegge, Michael J. Garay, Olga V. Kalashnikova, Anthony B. Davis, and Feng Xu

Abstract:
Our ESTO Instrument Incubator Program (IIP) Multiangle SpectroPolarimetric Imager (MSPI) technology development effort in support of the Decadal Survey Aerosol-Cloud-Ecosystem (ACE) mission has been aimed at advancing our understanding of the climate and air quality impacts of airborne particles (aerosols and clouds) using highly accurate spectropolarimetric imaging. Polarimetry provides valuable constraints on atmospheric particle optical and microphysical properties. Measurement requirements established by the ACE Science Working Group include ~0.005 uncertainty in degree of linear polarization (DOLP) over a wide swath and in multiple spectral bands. These are the principal drivers of our instrument approach. The Ground-based MSPI prototype (GroundMSPI) is an 8-band ultraviolet-visible-near infrared pushbroom camera, measuring polarization at 470, 660, and 865 nm. It is mounted on 2-axis gimbal, permitting scans in elevation angle that view both the surface and sky, as well as in azimuth angle. Our first generation airborne instrument, AirMSPI, acquires similar measurements as GroundMSPI, and is mounted on a single-axis gimbal to acquire multiangular observations over a ~67º along-track range from the NASA ER-2 high-altitude aircraft. The second generation AirMSPI-2 instrument adds a cirrus channel at 1888 nm, polarimetric capability at 1620 and 2185 nm, and narrowband radiance channels in the center and wing of the near-infrared O2 A-band to provide additional information on cloud microphysics and vertical structure. The technology challenges we addressed in designing and building these instruments included practical demonstration of the tandem photoelastic modulator polarization imaging technique, achromatic quarter waveplates covering a wide spectral range, miniaturized and integrated wiregrid polarizer and spectral filter assemblies, low noise and high speed linear detector array readouts, and construction of an extremely accurate partial polarization state generator for instrument polarimetric calibration and verification. Laboratory, field, and airborne data acquired using this suite of sensors will be shown to demonstrate the advances in polarimetric imaging technology accomplished as part of this work. Applications of the data to retrieval of surface, aerosol, and cloud microphysical properties, in conjunction with scattering theory to interpret the multiangular and multispectral observations, will be shown to demonstrate the unique benefits of polarimetry for missions such as ACE.