A43A-0261
On-board Polarimetric Calibration of Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) Measurements
Thursday, 17 December 2015
Poster Hall (Moscone South)
Gerard van Harten1, David J Diner1, Michael A Bull1, Irina N Tkatcheva1, Veljko M Jovanovic2, Felix C Seidel1, Michael J Garay2, Feng Xu3, Anthony B Davis1, Brian E Rheingans1 and Russell A Chipman4, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)Jet Propulsion Laboratory, Pasadena, CA, United States, (3)JPL/UCLA Joint Institute for Regional Earth System Science and Engineering, Pasadena, CA, United States, (4)University of Arizona, Tucson, AZ, United States
Abstract:
The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) aims at characterizing atmospheric aerosols and clouds using highly accurate imaging polarimetry. The instrument is deployed regularly onboard the NASA ER2 high-altitude aircraft, which is an ideal testbed for satellite remote sensing. Flying at 20 km altitude, AirMSPI’s pushbroom camera typically provides 11×11 km images at 10 m resolution. The target is observed from multiple along-track angles within ±67° using a gimbal mount. Eight spectral bands within 355-935 nm are recorded simultaneously in different detector rows, 3 of which also measure linear polarization: 470, 660 and 865 nm. Photoelastic modulators (PEMs) encode the polarized and total intensities in each polarimetric pixel as the amplitude and offset of a wavelike intensity pattern, such that the ratio of the two is insensitive to pixel-to-pixel differences. This enables an accuracy in the degree of linear polarization of ~0.001, as measured in the lab. To maintain this accuracy in-flight, an optical probe continuously monitors the PEMs’ retardances and controls their driving signals. Before and after observing a target, the instrument also observes a validator, which is an extended, polarized light source, located inside the instrument housing. These data are now incorporated in the data processing pipeline to further improve the calibration of the modulation functions. Highly polarized pixels in Earth data are utilized to transfer the validator results to meet the illumination in Earth scenes, as well as to make fine adjustments at higher temporal resolution. The reprocessed polarization products for the PODEX campaign show significant improvements when intercompared with the Research Scanning Polarimeter (RSP, Goddard Institute for Space Studies). We currently evaluate the impact of the on-board polarimetric calibration on aerosol retrievals, and compare against AERONET reference measurements.
