Polarization measurements can be used to differentiate objects of different geometry and material. Polarimetry has been used as a tool to differentiate between two composite geometries, each comprised of a model satellite bus, a solar panel, and a dish antenna. Each component demonstrates unique polarization signatures that can be obtained by analyzing the reflection of passive illumination. An approach for characterizing geometries using Stokes vector–vector space has been demonstrated to be very effective in differentiating between composite geometries representative of orbiting satellites. Our approach lends itself well to a statistical analysis that is applicable for a computational method to provide target identification of space objects.
Polarization measurements can be used to distinguish different objects. In this work, polarimetry has
been used as a useful tool to differentiate between two geometries, viz., a cube and a cylinder, demonstrating
that polarization “signatures” can be obtained from the reflection of passive lighting. A novel approach to
characterizing geometries using vector-vector space has been demonstrated to be effective in differentiating
between these two geometries and lends itself well to a statistical analysis that is applicable for computer
generated target identification.
Digital holography uses phase imaging in a variety of techniques to produce a three-dimensional phase
resolved image that includes accurate depth information about the object of interest. Multi-wavelength digital
holography is an accurate method for measuring the topography of surfaces. Typically, the object phases are
reconstructed for two wavelengths separately and the phase corresponding to the synthetic wavelength (obtained
from the two wavelengths) is obtained by calculating the phase difference. Then the surface map can be obtained
using proper phase-unwrapping techniques. Usually these synthetic wavelengths are on the order of microns which
can be used to resolve depths on the order of microns. In this work, two extremely close wavelengths generated
by an acousto-optic modulator (AOM) are used to perform two-wavelength digital holography. Since the
difference between the two wavelengths is on the order of picometers, a large synthetic wavelength (on the order
of centimeters) can be obtained which can be used to determine the topography of macroscopic surface features.
Also since the synthetic wavelength is large, an accurate surface map can be obtained without using a phase-unwrapping
technique. A 514 nm Argon-ion laser is used as the optical source, and used with an AOM to generate
the zeroth-order and frequency-shifted first-order diffracted orders which are used as the two wavelengths. Both
beams are aligned through the same spatial filter assembly. Holograms are captured sequentially using a typical
Mach-Zehnder interferometric setup by blocking one beam at a time. Limitations of the large synthetic wavelength
are also discussed.
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