Polarization Signatures in Vector Space

Date of Award

2018

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics

Advisor/Chair

Advisor: Partha Banerjee

Abstract

The use of polarimetric information to enhance the identification process for unresolved and unknown targets in GEO orbit is quite rare. The majority of observations made of objects at that distance are spectral measurements, without the polarization information that is available in the same stream of photons being captured. It is proposed to use polarimetric signatures to enhance the speed and accuracy of the identification of unknown objects. Three methods of polarization signatures are proposed. First, the standard Stokes signature plotted as a function of solar phase angle is recommended. But beyond that, two other methods are proposed to help qualitative and quantitative assessment of the unknown target. The second method is the use of vector space, a ratio of one Stokes parameter to another in all combinations possible (six spaces), plotted against the solar phase angle in a similar manner to the Stokes signatures. The third method is novel, using a technique borrowed from astronomers who characterize distant stars based on color-color analysis of the intensity ratios of celestial objects. A statistical method of analyzing the resulting object characterization is also proposed, which is the Bhattacharyya distance, a non-Euclidean method to characterize the clusters produced by the third method. The experiments were conducted comparing simple geometries with one another to determine if polarization could differentiate simple geometries. Next different materials and surfaces were compared with one another to test polarization as a differentiator of the materials. Third, two complex models made up of three simple geometries that are representative of satellite construction were built and tested by the same three methods, to differentiate them from each other based on polarization signatures. Last, a third composite, different than both previous composites was built, and the method tested to see if it would identify the geometry most dissimilar to the new object so that a selection process could be created.Each of the polarization methods tested was successful in differentiating geometry, material, surface configuration, and complex composite geometries made up of the simpler geometries tested. Polarization signatures are ubiquitous and consistent. It was found that the peaks and valleys observed in the signatures of compound objects were caused by the geometry and material of the simpler parts making up the complex object. A selection procedure was demonstrated based on identifying the most dissimilar object of two choices, and eliminating it. Polarization signatures were capable of differentiating which objects were most like and most dissimilar to the test object. In conclusion, using polarimetry as an analytical tool to help identify unresolved objects in space is potentially an excellent process that would complement current methods of spectral analysis.

Keywords

Electrical Engineering, Optics, polarization, statistical polarimetry, target identification, polarization signatures

Rights Statement

Copyright © 2018, author

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