Measurements of the Opposition Effect in the Visible and Near-Infrared Using an Improvised Imaging Spectropolarimeter




Foster, Kyle A.

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Spectropolarimetry is a remote sensing technique that combines both spectral and polarimetric measurements. It is already well-established in the astronomical community as an indispensable tool, permitting characterization of dust clouds and stars, and enhancing observations of planetary bodies. One such noteworthy phenomenon is the opposition effect, wherein a planetary body such as the Moon exhibits a surge in reflected intensity as the phase angle—an angle between the Sun, the Moon, and the observer—decreases to below approximately five degrees. Astronomical and laboratory investigations into the opposition effect reveal that the light of this surge often has a polarized component. The terrestrial remote sensing community is starting to develop an interest in spectropolarimetry. Spectral and polarimetric measurements alone, while useful in their diverse applications, stand to benefit from the added dimensionality that spectropolarimetric measurements provide. Examples of applications that benefit from spectropolarimetric measurement include environmental monitoring, search & rescue, and countering denial and deception techniques. To that end, an improvised imaging spectropolarimeter sensitive in the visible and near-infrared spectrum has been developed by attaching a linear polarization filter to a SOC700 hyperspectral imaging system for use in further development of spectropolarimetric applications. The results of three research objectives are reported upon. First, validation of the operation of the improvised imaging spectropolarimeter and the resulting data calibration and processing techniques, including generating Stokes parameter imagery, is successfully completed. Second, demonstrating that the improvised system is capable of observing the opposition effect in a laboratory setting is also confirmed. Third, the improvised system is used to characterize various materials—including rare earth element oxides and ultra-high performance concrete—in various phase angle geometries, with the intent of determining whether the polarized component of the opposition effect yields sufficient additional information for material detection and identification.



Spectropolarimetry, Polarimetric imaging, Hyperspectral imaging, Stokes imagery, Opposition effect, Visible and near-infrared