This PDF file contains the front matter associated with SPIE Proceedings Volume 9099, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

A camera capable of obtaining single snap-shot, quantitative, polarimetric measurements is investigated to determine performance characteristics. The camera employs a micropolarizer array with linear polarizers oriented at 0, 45, 90, and, 135 degrees. Micropolarizer arrays with elements as small as 7.4 microns and arrays as large 4 million pixels have been fabricated for use across the visible spectrum. The pixelated polarization camera acquires the four polarization orientations in a single video frame, which enables instantaneous measurements of the linear Stokes parameters. Examples of calibration methods and the results of controlled experiments are presented. Error sources and methods for minimizing them are discussed and demonstrated. A practical example of measuring stress induced birefringence is demonstrated.

Polarization, flux, and the spectral energy distribution of light are the fundamental parameters that we measure in order to infer properties of the sources of electromagnetic radiation, such as intensity, temperature, chemical composition and physical geometry. Recently, the fabrication of microgrid polarizer arrays (MPAs) facilitated the development of a new class of division-of-focal plane polarimeters. These devices are capable of measuring the degree and angle of polarization across a scene with a single exposure. We present the design of the Rochester Institute of Technology Polarization Imaging Camera (RITPIC), a snapshot polarimeter for visible and near-infrared remote sensing applications. RITPIC is a compact, light-weight and mechanically robust imaging polarimeter that is deployable on terrestrial, naval, airborne and space-based platforms. RITPIC is developed using commercially available components and is capable of fast cadence imaging polarimetry of a wide variety of scenes. We derive the expected performance of RITPIC using the first high resolution 3D finite-difference time-domain (FDTD) models of these hybrid focal planes and simulated observations of synthetic scenes rendered with the Digital Imaging and Remote Sensing Image Generation (DIRSIG) model. Furthermore, we explore applications in remote sensing for which RITPIC, and devices like it, provide unique advantages.

Image interpolation and denoising are important techniques in image processing. Recently, there has been a growing interest in the use of Gaussian processes (GP) regression for interpolation and denoising of image data. However, exact GP regression suffers from 0 (N³) runtime for data size N, making it intractable for image data. Our GP-grid algorithm reduces the runtime complexity of GP from 0 (N³) to 0 (N³1²). We provide comprehensive mathematical model as well as experimental results of the GP interpolation performance for division of focal plane polarimeter. The GP interpolation method outperforms the commonly used bilinear interpolation method for polarimeters.

Microgrid polarimetric imagers sacrifice spatial resolution for sensitivity to states of linear polarization. We have recently shown that a 2 × 4 microgrid analyzer pattern sacrifices less spatial resolution than the conventional 2× 2 case without compromising polarization sensitivity. In this paper, we discuss the design strategy that uncovered the spatial resolution benefits of the 2 × 4 array.

A continuously operating all-sky polarization imager recorded the skylight polarization pattern as conditions transitioned from clear and clean to extremely smoky. This transition included a period when a local wildfire plume filled part of the sky with smoke, creating a highly asymmetric distribution of aerosols. Multiple scattering in the smoke plume strongly reduced the degree of polarization in the smoky region of the sky. Once the smoke plume spread out to cover the entire local sky, the degree of polarization was strongly reduced everywhere. However, this example differed from previously observed smoke events because, even though the usual skylight polarization pattern generally persisted throughout the event, this time the smoke-covered sky exhibited a spatially asymmetric profile along the band of maximum polarization. This pattern of reduced polarization toward the horizon is hypothesized to be a result of an optically thick but physically thin smoke layer. The skylight polarization observations are supplemented with optical depth measurements and aerosol size distribution retrievals from a solar radiometer.

We present both simulation and experimental results showing that circularly polarized light maintains its degree of polarization better than linearly polarized light in scattering environments. This is specifically true in turbid environments like fog and clouds. In contrast to previous studies that propagate single wavelengths through broad particle-size distributions, this work identifies regions where circular polarization persists further than linear by systematically surveying different wavelengths through monodisperse particle diameters. For monodisperse polystyrene microspheres in water, for particle diameters of 0.99 and 1.925 microns and varying optical depths, we show that circular polarization’s ability to persist through multiple scattering events is enhanced by as much as a factor of four, when compared to that of linear polarization. These particle diameters correspond to size parameters found for infrared wavelengths and marine and continental fog particle distributions. The experimental results are compared to Monte Carlo simulations for all scattering environments investigated.

We report the main conclusions from an interactive, multidisciplinary workshop on “Polarimetric Techniques and Technology”, held on March 24-28 2014 at the Lorentz Center in Leiden, the Netherlands. The work- shop brought together polarimetrists from different research fields. Participants had backgrounds ranging from academia to industrial RD. Here we provide an overview of polarimetric instrumentation in the optical regime geared towards a wide range of applications: atmospheric remote sensing, target detection, astronomy, biomedical applications, etc. We identify common approaches and challenges. We list novel polarimetric techniques and polarization technologies that enable promising new solutions. We conclude with recommendations to the polarimetric community at large on joint efforts for exchanging expertise.

Activity Based Intelligence (ABI) is the derivation of information from the composite of a series of individual actions being recorded over a period of time. Due to its temporal nature, ABI is usually developed from Motion Imagery (MI) or Full Motion Video (FMV) taken of a given scene. One of today's common issues is sifting through such large volumes of temporal data. Here we propose using a technique known as tipping an cueing to alleviate the need to manually sift through said data. Being able to tip the analysts or automated algorithm towards a particular person or object in the data is useful in reducing search time. We propose using a polarimetric sensor to identify objects of interest, in a scene where their signature would be unusual. Once identified, this data will be used to cue a FMV RGB sensor to track the object and determine the activities being executed by the person bringing the object into the scene.

The reflective bands in modern imaging, i.e., the visible through the short wave infrared (SWIR), have become very attractive for use in both daytime and low light target acquisition and surveillance. In addition, the nature of the target in modern conflict again includes the human body as a principle target. The spectral natures of the reflectivities of humans, their clothing, what they may be carrying, and the environments in which they are immersed, along with the spectral nature and strength of the light sources that illuminate them, have been the essential components of the contrasts in the signatures that are used in models that predict probabilities of target acquisition and discrimination. What has been missing is the impact that polarization in these signatures can have on image contrast. This paper documents a preliminary investigation into the contrast in active and passive polarimetric signatures of humans holding two-handed objects in the SWIR.

The proposed paper recommends a new anomaly detection algorithm for polarimetric remote sensing applications based on the M-Box covariance test by taking advantage of key features found in a multi-polarimetric data cube. The paper demonstrates: 1) that independent polarization measurements contain information suitable for manmade object discrimination from natural clutter; 2) analysis between the variability exhibited by manmade objects relative to natural clutter; 3) comparison between the proposed M-Box covariance test with Stokes parameters S₀ and S₁, DoLP, RX­ Stokes, and PCA RX-Stokes; and finally 4) the data used for the comparison spans a full24-hour measurement.

We present a series of long-wave-infrared (LWIR) polarimetric-based thermal images of facial profiles in which polarization-state information of the image forming radiance is retained and displayed. The resultant polarimetric images show enhanced facial features, additional texture, and details that are not present in the corresponding conventional thermal imagery. It has been generally thought that conventional thermal imagery (MidiR or LWIR) could not produce the detailed spatial information required for reliable human identification due to the so-called "ghosting" effect often seen in thermal imagery of human subjects. By using polarimetric information, we are able to extract subtle surface features of the human face, thus improving subject identification. The considered polarimetric image sets include the conventional thermal intensity image, S₀ , the two Stokes images, S₁ and S₂, and a Stokes image product called the degree-of-linear-polarization (DoLP) image. Finally, Stokes imagery is combined with Fresnel relations to extract additional 3D surface information.

Image registration is a digital image processing technique that takes two or more of images of a scene in different coordinate systems and transforms them into a single coordinate system. Image registration is a necessary step in many advanced image processing techniques, such as multi-frame super-resolution. For that reason, registration accuracy is very crucial. While image registration is usually performed on images, one can perform the registration using metric images as well. This paper will present registration methods and their accuracies for various noise levels for the case of pure translational image motion. Registration techniques will be applied to the images themselves as well as to phase congruency images, gradient images, and edge-detected images. This study will also investigate registration of under-sampled images. Noise-free images are degraded using three types of noise: additive Gaussian noise, fixed-pattern noise along the column direction, and a combination of these two. The registration error is quantified for two registration algorithms with three different images as a function of the signal-to-noise ratio. A test on the usefulness of the image registration and registration accuracy performed on the intensity images of the Stokes imaging polarimeter. The Stokes images calculated before and after registration of the intensity images are compared to each other to show the improvement.

Objective and background: We present a new method for the calibration of Bossa Nova Technologies’ full Stokes, passive polarization imaging camera SALSA. The SALSA camera is a Division of Time Imaging Polarimeter. It uses custom made Ferroelectric Liquid Crystals mounted directly in front of the camera’s CCD. Regular calibration process based on Data Reduction Matrix calculation assumes a perfect spatial uniformity of the FLC. However, alignment of FLC molecules can be disturbed by external constraints like mechanical stress from fixture, temperature variations and humidity. This disarray of the FLC molecules alignment appears as spatial non-uniformity. With typical DRM condition numbers of 2 to 5, the influence on DOLP and DOCP variations over the field of view can get up to 10%. Spatial nonuniformity of commercially available FLC products is the limiting factor for achieving reliable performances over the whole camera’s field of view. We developed a field calibration technique based on mapping the CCD into areas of interest, then applying the DRM calculations on those individual areas. Results: First, we provide general background of the SALSA camera’s technology, its performances and limitations. Detailed analysis of commercially available FLCs is described. Particularly, the spatial non uniformity influence on the Stokes parameters. Then, the new calibration technique is presented. Several configurations and parameters are tested: even division of the CCD into square-shaped regions, the number of regions, adaptive regions. Finally, the spatial DRM “stitching” process is described, especially for live calculation and display of Stokes parameters.

Polarimetric hyperspectral imaging (P-HSI) has the potential to improve target detection, material identification, and background characterization over conventional hyperspectral imaging and polarimetric imaging. To fully exploit the spectro-polarimetric signatures captured by such an instrument, a careful calibration process is required to remove the spectrally- and polarimetrically-dependent system response (gain). Calibration of instruments operating in the long-wave infrared (LWIR, 8μm to 12 μm) is further complicated by the polarized spectral radiation generated within the instrument (offset). This paper presents a calibration methodology developed for a LWIR Telops Hyper-Cam modified for polarimetry by replacing the entrance window with a rotatable holographic wire-grid polarizer (4000 line/mm, ZnSe substrate, 350:1 extinction ratio). A standard Fourier-transform spectrometer (FTS) spectro-radiometric calibration is modified to include a Mueller-matrix approach to account for polarized transmission through and polarized selfemission from each optical interface. It is demonstrated that under the ideal polarizer assumption, two distinct blackbody measurements at polarizer angles of 0°, 45°, 90°, and 135° are sufficient to calibrate the system for apparent degree-of-linear-polarization (DoLP) measurements. Noise-equivalent s₁, s₂, and DoLP are quantified using a wide-area blackbody. A polarization-state generator is used to determine the Mueller deviation matrix. Finally, a realistic scene involving buildings, cars, sky radiance, and natural vegetation is presented.

Phase error is common in reflective interferometers, such as the Michelson. This yields highly asymmetric interferograms that complicate the post-processing of single-sided interference data. Common methods of compensating for phase errors include the Mertz, Forman, and Cannes phase correction techniques. However, birefringent interferometers often have highly symmetric interferograms; thus, compensating for phase errors may represent an unnecessary and/or detrimental step in post processing. In this paper, an analysis of the phase error generated by the Infrared Hyperspectral Imaging Polarimeter (IHIP) is conducted. First, a model of the IHIP is presented that quantifies the phase error in the system. The error associated with calculating spectra from single-sided interferograms, using Mertz phase correction and simple single­sided to double-sided mirroring, is then investigated and compared to "true" double-sided Cannes phase corrected spectra. These error calculations are set within the context of measurements taken from a Michelson interferometer-based Fourier transform spectrometer. Results demonstrate that the phase error of the IHIP is comparatively small and that Mertz phase correction may not be necessary to minimize error in the spectral calculation.

We present implementations of optical instrumentation that records five dimensions of light: polarization state as a function of wavelength, two spatial dimensions, and time. We focus on the optimal integration of polarimetry within microlens-based integral-field spectroscopy. The polarimetric analyzer (or beam-splitter) and dispersing element could be implemented separately, but also amalgamated in the form of a polarization grating. We present optimizations for stacking the polarization-split spectra on a 2D detector. The polarimetric modulation can be performed in the temporal, the spatial or the spectral domain. Temporal modulation could be set up with achromatic optics conform the Stokes definition scheme, but a wide wavelength range generally demands a “polychromatic” modulation approach for which the modulation efficiency for all or some of the Stokes parameters is optimized at every wavelength. Spectral modulation (full-Stokes or optimized for linear polarization) yields instruments without any moving parts, for which all polarization information is obtained in one shot. We present first results from two polarimetric IFU instruments; the ExPo pIFU and LOUPE. The first is based on a rapid polychromatic modulator consisting of two FLCs and two fixed retarders, while the latter is based on spectral modulation for linear polarization. In addition to applications within astronomy and planetary science, we discuss remote-sensing applications for such instruments.

High speed spectral imaging is useful for a variety of tasks spanning industrial monitoring, target detection, and chemical identification. To better meet these needs, compact hyperspectral imaging instrumentation, capable of high spectral resolution and real-time data acquisition and processing, are required. In this paper, we describe the first snapshot imaging spatial heterodyne Fourier transform spectrometer based on birefringent crystals and polarization gratings. This includes details about its architecture, as well as our preliminary proof of concept. Finally, we discuss details related to the calibration of the sensor, including our preliminary investigations into high speed data reconstruction and calibration using neural networks. With such an approach, it may be feasible to reconstruct and calibrate an entire interferogram cube in one step with minimal Fast Fourier Transform (FFT) processing.

Development of two prototype field-portable hyperspectral imagers that will also collect polarization signatures is being carried out in the visible-near infrared (VNIR) and the shortwave infrared (SWIR) regions. Each of these imagers uses a TeO₂ noncollinear acousto-optic tunable filter (AOTF) and two liquid crystal variable retarders (LCVRs). The spectral region of operation for the first imager is from 400 to 800 nm and for the second one from 900 to 1700 nm. We will present the optical design and Mueller Matrix analysis results.

Mueller matrix microscopy is the natural generalization of polarization microscopy. It provides images of the Mueller matrix of a sample with micrometric resolution. In this work we describe a Mueller matrix microscope that uses the dual rotating compensator technique to simultaneously determine all the elements of its transmission or reflection Mueller matrix. The instrument uses two compensators that rotate at different frequencies and every Mueller matrix element is determined by using a digital frequency demodulation technique that does the frequency-analysis of the time dependent intensity captured at every pixel of the CCD detector. Transmission and reflection measurements are illustrated with experimental examples.

Digital diagnostic pathology has become one of the most valuable and convenient advancements in technology over the past years. It allows us to acquire, store and analyze pathological information from the images of histological and immunohistochemical glass slides which are scanned to create digital slides. In this study, efficient fractal, wavelet-based polarimetric techniques for histological analysis of monolayer lung cancer cells will be introduced and different monolayer cancer lines will be studied. The outcome of this study indicates that application of fractal, wavelet polarimetric principles towards the analysis of squamous carcinoma and adenocarcinoma cancer cell lines may be proved extremely useful in discriminating among healthy and lung cancer cells as well as differentiating among different lung cancer cells.

3D-Polarized Light Imaging (3D-PLI) is a unique technique that enables high-resolution three-dimensional mapping of the nerve fiber architecture in unstained histological sections of the human brain. 3D-PLI is based on the detection of the intrinsic tissue birefringence caused by the nerve fibers. The measured birefringent signals comprise entangled information on both spatial fiber orientation and the local fiber density. In this study, we introduce a novel approach to effectively and unambiguously unravel this interrelation, for providing a reliable estimation of fiber orientations in the entire human brain. The method relies on an in-house developed polarimetric device equipped with a tiltable specimen stage. Each brain section is measured from different perspectives and the obtained data sets are processed with a dedicated Fourier analysis optimized for fast computation and shot noise stability. For the first time it is demonstrated, that the prevailing orientations of cortical fibers can be quantified in the three-dimensional space and traced back into the white matter. Moreover, the approach provides descriptions of variances in fiber density. Hence, the method presented here opens new perspectives for the neuroanatomical study of the human cortex.

Polarized light fields contain more information than simple irradiance and such capabilities provide an advanced tool for underwater imaging. We used a Monte Carlo technique to simulate the vector point spread function for a broad range of water parameters from clear to turbid coastal waters. We also analyzed the impact of light scattered by suspended particles between the target and the camera on the polarized image together with the light from the target. This knowledge is expected to contribute to solutions of the inverse problem of the restoration of the target polarization characteristics from its underwater image.

We introduce and demonstrate an approach to create highly chromatic retardation spectra across various wave­ lengths. The design approach is based on Multi-Twist Retarder (MTR) principle where multiple liquid crystal polymer layers are coated on top of each other on a single substrate. Previous MTRs have been applied to develop broadband achromatic retarders, but here we show that MTRs are quite flexible, and their retardation spectrum can be tuned to create arbitrary profiles. As a representative example, we show this tailorability by creating a retarder which produces approximately zero retardation in visible (500-900 nm) and half-wave retardation in near- infrared (1-2.7 μm) wavelength region. This would provide enhancement in remote sensing, telecom, and spectroscopy systems where it is advantageous to have an optical element which affects only one band, but is largely transparent otherwise.

Liquid crystal (LC) technology, a critical component in a diverse range of optics for visible wavelengths, has recently been adapted into devices for the mid-wave infrared (MWIR). Optics designs, including variable retarders, attenuators, linear polarization rotators, and tunable filters, have been modified for optimal performance over the range of 3.6 to 5.7 microns. We constructed these designs using material selected for optimal optical behavior in this wavelength range. Description and characterization of these chosen component materials is included along with the performance of each device. We present design challenges, along with future plans and possibilities for MWlR LC technology.

This paper will present the first prototypes of vortex retarders made of photo-orientable liquid crystals polymers recorded without mechanical action using only polarization holography. Vortex retarders are birefringent plates characterized by a uniform phase retard and a rotation of their fast axis along their center. Liquid crystals are anisotropic molecules possessing birefringent properties. They are locally orientable and their orientation defines the fast axis orientation of the retarder. Their alignment depends on the local orientation of the recording electric field. The superimposition of several polarized beams will be used to shape the electric field to achieve the recording of vortex retarders. The mathematical aspects of the superimposition process, as well as several numerical simulations are exposed. Finally, the first prototypes are presented, characterized and compared to the numerical simulations.

Photoelastic modulators (PEMs) are among the most robust and precise polarization modulation devices, but the high frequency free-running nature of PEMs challenges their incorporation into relatively slow CCD and CMOS imaging systems. Current methods to make PEMs compatible with imaging suffer from low light throughput or use high cost intensified CCDs. They are not ideal for some analyses (microscopy, reflectivity, fluorescence, etc.), and likely cannot be extended to polarimeters with more than two PEMs. We propose to modulate the light source with a square wave derived from particular linear combinations of the elementary PEM frequencies and phases. The real-time synthesis of the square waves can be achieved using a field programmable gate array (FPGA). Here we describe the operating principle.

The aim of this work is to present a multi-band absorption metamaterials. One dual cross-shape perfect absorber metamaterials (PAMs) was developed to obtain multi-band spectrum at mid-infrared. The PAMs possess three distinct resonant peaks standing independently, which are attributed to the polarization sensitive excitation of plasmonic resonance. The optical parameters retrieved by S-parameters method were investigated, which provides a satisfactory qualitative description of the multiple-band spectra responses. On the other hand, the near-field plasmonic behaviors and redistribution of the electromagnetic field were probed theoretically and numerically into the PAMs structure, which also explains the observed absorption behavior of the PAMs ensemble based upon the microscopic perspective. The multiplex spectrum enables the infrared perfect absorber metamaterials (PAMs) a powerful tool for direct access to vibrational fingerprints of single molecular structure.

The most common method of polarimetery involves imaging a scene through a polarization analyzer at multiple configurations. Switching among these configurations requires capturing multiple images of the scene, limiting the ability to capture real-time polarization data due to multiple scene sampling and motion artifacts. Advances in nanofabrication technology have allowed direct integration of polarization analyzers onto the sensor, enabling the capture of multiple analyzer intensities from a single frame. Using this technique, we have fabricated a high frame rate, VGA resolution, division of focal plane polarization imager for the visible spectrum. The imaging sensor is realized by monolithic integration of aluminum nanowires with an array of CCD imaging elements. The pixelated nanowire polarization filters are at four different orientations offset by 45° This allows for recording of the first three Stokes parameters at every super pixel, and subsequently the degree of linear polarization and angle of polarization are computed at 250 frames per second at full VGA resolution and over 1000 when limited to a subsection of the array. The imaging sensor also employs a per pixel calibration scheme which mitigates the variations in the aluminum nanowire sizes. We present an optical characterization of the sensor, and then utilize the increased frame rate to capture high speed polarization images of pieces of polycarbonate plastic placed under stress. The high frame rate allows us to recover strain information that regular rate sensors cannot.

The light scattered by plant canopies depends in part on the light scattering/absorbing properties of the leaves and is key to understanding the remote sensing process in the optical domain. Here we specifically looked for evidence of fine spectral detail in the polarized portion of the light reflected from the individual leaves of five species of plants measured at Brewsters angle over the wavelength range 450 to 2300nm. Our results show no strong, unambiguous evidence of narrow band spectral variation of the polarized portion of the reflectance factor.

The polarization measurement instrument of land objects is a key element of the polarization remote sensing research, especially for the polarized spectral measurement. The current non-real time and partial polarization spectral measurement cannot meet the need of study. In this paper, a real time full-Stokes spectro-polarimeter with Deuterated Potassium Dihydrogen Phosphate (KD*P) crystals was developed in lab. The polarimeter, consisting of two KD*Ps and a fixed retarder and a polarizer, can measure the full Stokes vector with a flexible modulation frequency 1Hz-1kHz, and has the balanced polarimetric efficiencies at a wide spectra band of 400-900 nm. The polarimeter was calibrated with an instrument calibration unit (ICU) to determine the instrument matrix X of each band using a non-linear least square fitting method, the results showed that the measuring accuracy of the full-Stokes spectro-polarimeter is better than 0.02 over the entire spectra band after calibration. Besides, Rohdea japonica is measured and analyzed to obtain their full polarization properties, and the results demonstrated that the circular polarization parameter V is not small enough to be neglected but show significant band features.

We present a collective, integrative view and a comprehensive, detailed analysis of the singleelement polarizer (SEP) instrument, where it is composed of only a polarizer in the incident beam. A light detector receives the reflected beam from the sample, which is a film-substrate system in general. Seven modes of operation of this instrument are discussed; seven techniques of ellipsometry, reflecsometry (defined as ellipsometry-based reflectometry), elliptometry (defined as reflectometry-based ellipsometry), and reflectometry. First: one ellipsometer is where the polarizer is rotated and the angle of incidence is scanned for a specific condition of the detector signal. That way, specific corresponding points in the ρ-plane of the film-substrate sample are detected. Second: another ellipsometer is where the polarizer is rotated and the angle of incidence is kept un-changed, and the ac/dc signal ratio is detected, yielding the ellipsometric angle ψ of the sample. Third: one reflecsometer is where the angle of incidence is scanned, while the polarizer is stationary, and a specific condition of the detector signal is detected, indicating a corresponding specific condition of the sample performance. Four more techniques of ellipsometry, reflecsometry, elliptometry, or reflectometry are also presented. For all modes of operation, heuristic and/or mathematical inversion methods exist to fully characterize the film-substrate system: determine the substrate optical constant and that of the film, in addition to the film thickness, or a subset thereof. We briefly present some of the available inversion methods with reference to the SiO2-Si film-substrate system in some cases.