This PDF file contains the front matter associated with SPIE Proceedings Volume 7672, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Recently, the use of imaging polarimetry has received considerable attention for use in automatic target recognition (ATR) applications. In military remote sensing applications, there is a great demand for sensors that are capable of discriminating between real targets and decoys. Accurate discrimination of decoys from real targets is a challenging task and often requires the fusion of various sensor modalities that operate simultaneously. In this paper, we use a simple linear fusion technique known as the high-boost fusion method for effective discrimination of real targets in the presence of multiple decoys. The HBF assigns more weight to the polarization-based imagery in forming the final fused image that is used for detection. We have captured both intensity and polarization-based imagery from an experimental laboratory arrangement containing a mixture of sand/dirt, rocks, vegetation, and other objects for the purpose of simulating scenery that would be acquired in a remote sensing military application. A target object and three decoys that are identical in physical appearance (shape, surface structure and color) and different in material composition have also been placed in the scene. We use the wavelet-filter joint transform correlation (WFJTC) technique to perform detection between input scenery and the target object. Our results show that use of the HBF method increases the correlation performance metrics associated with the WFJTC-based detection process when compared to using either the traditional intensity or polarization-based images.

We present a novel polarization based metrological method of 3D shape measurement for in-line control of optical surfaces and control of highly aspheric optical surfaces. This technique is fast, non contact, high resolution, alignment free and with unprecedented dynamic. It has the potential to reach tens of nanometers accuracy. In this paper we show that a polarization imaging camera combined with an un-polarized illumination and 3D reconstruction algorithm lead to the 3D reconstruction of optical element (regular lens and aspheric lens) and the measurement of their parameters. The optical element to be measured is placed in a diffusive integrating sphere and illuminated by un-polarized light. The reflection of the un-polarized light by the optical element gets partially polarized. A polarization camera captures the image of the optical element and measures the polarization state of each pixel in real time. The Degree Of Light Polarized and the Angle Of Polarization parameters are related to the geometry of the optical element. The 3D shape of the optical element is reconstructed using dedicated software. The architecture of the hardware, calibration results and sensitivity measurements is presented and experimental results and observations as well as possible further steps and new applications are discussed.

Polarimetric remote sensing has demonstrated utility for improving contrast between man-made targets and complex backgrounds. More specifically, polarimetric signatures of man-made targets can be useful for cueing analysts in widearea search applications. However, taking the target cueing to the next level of identification and tracking may require tasking of other sensing modalities. We present research that aims to understand what pose information might be extracted from the polarimetric signatures of under-resolved targets. Through experimentally collected and simulated imagery, we examine the variation in target signatures with respect pose and the relative sensor position aiming to extend the intelligence value of polarimetric imagery.

We present a comparative study involving five distinctly different polarimetric imaging platforms that are designed to record calibrated Stokes images (and associated polarimetric products) in either the MidIR or LWIR spectral regions. The data set used in this study was recorded during April 14-18, 2008, at the Russell Tower Measurement Facility, Redstone Arsenal, Huntsville, AL. Four of the five camera systems were designed to operate in the LWIR (approx. 8-12μm), and used either cooled mercury cadmium telluride (MCT) focal-plane-arrays (FPA), or a near-room temperature microbolometer. The lone MidIR polarimetric sensor was based on a liquid nitrogen (LN2) cooled indium antimonide (InSb) FPA, resulting in an approximate wavelength response of 3-5μm. The selection of cameras was comprised of the following optical designs: a LWIR "super-pixel," or division-of-focal plane (DoFP) sensor; two LWIR spinning-achromatic-retarder (SAR) based sensors; one LWIR division-of-amplitude (DoAM) sensor; and one MidIR division-of-aperture (DoA) sensor. Cross-sensor comparisons were conducted by examining calibrated Stokes images (e.g., S0, S1, S2, and degree-of-linear polarization (DOLP)) recorded by each sensor for a given target at approximately the same test periods to ensure that data sets were recorded under similar atmospheric conditions. Target detections are applied to the image set for each polarimetric sensor for further comparison, i.e., conventional receiver operating characteristic (ROC) curve analysis and an effective contrast ratio are considered.

There is a strong need for the ability to terrestrially image resident space objects (RSOs) and other low earth orbit (LEO) objects for Space Situational Awareness (SSA) applications. The Synthetic Aperture Imaging Polarimeter (SAIP) investigates an alternative means for imaging an object in LEO illuminated by laser radiation. A prototype array consisting of 36 division of amplitude polarimeters was built and tested. The design, assembly procedure, calibration data and test results are presented. All 36 polarimeters were calibrated to a high degree of accuracy. Pupil plane imaging tests were performed in by using cross-correlation image reconstruction algorithm to determine the prototype functionality.

Polarimetric sensors are valued for their capability to distinguish man-made objects from surrounding clutter. The SPITFIRE (Spectral Polarimetric Imaging Test Field InstRumEnt) polarimetric camera is designed to function in multiple bands in the Short Wave Infrared (SWIR) and Mid-Wave Infrared (MWIR) regions. SPITFIRE is a Stokes micro-grid polarimetric system with a 4 band spectral filter wheel. The focal plane array (FPA) as well as the filter wheel are located in a Dewar which is cooled via liquid nitrogen. By cooling the band-pass filter to the same temperature as the FPA, self-emission noise is decreased. In this paper we discuss the design and fabrication of the polarimetric camera (optics, Dewar, filter wheel and FPA), the data capture and processing system, initial characterization of the camera's performance, and future plans for the camera.

We have introduced the concept of a snapshot imaging spectropolarimeter based on anisotropic diffraction gratings known as Polarization Gratings (PGs). This instrument can acquire both spectral and polarization information of an object by using the unique optical properties of PGs, which create a diffraction pattern on a single focal plane array. In this paper we develop a system matrix for reconstructing the object information from this diffraction pattern. This matrix is extendable to various configurations containing several PGs. Moreover, we demonstrate an imaging spectropolarimeter based on this approach, that was used to reconstruct both screen generated scenes and outdoor objects. Reconstructed objects are sampled at 100 ×100 × 51 (x, y, λ) with 4 nm spectral resolution.

A common technique, referred to as channeled imaging polarimetry (CIP), enables the snapshot acquisition of the 2- dimensional Stokes parameters of an arbitrary scene or sample. It achieves this by amplitude modulating the Stokes parameters onto various interference-based spatial carrier frequencies. While this technique has utility, it often suffers from low signal-to-noise ratios in remote sensing scenarios, since it requires narrow spectral bandwidth illumination (< 3 nm in the visible). This paper discusses one hardware implementation that can be utilized to overcome this limitation. Consequently, an overview of the theoretical and experimental development of this system, a uniquely modified Sagnac interferometer, is discussed. Both laboratory and outdoor data are included to demonstrate the instrument's ability to measure polarization in arbitrary scenes. Inclusion of blazed diffraction gratings inside the interferometer enables whitelight interference fringes to be generated. By incorporating these gratings, the operational bandwidth of the interference fringes can exceed approximately 300 nm within the visible spectrum; two orders of magnitude greater than previous CIP implementations. Lastly, by modifying the diffraction grating, the sensor becomes capable of snapshot multispectral imaging. This is briefly discussed, with both a theoretical description and experimental data.

With the increasing use of polarization as an added dimension in imagery for a variety of scientific, defense, and civilian applications comes a need for better understanding of how the natural environment affects polarization signatures. In the visible and near-infrared spectral range, the most important environmental component is polarized skylight. To provide data to help improve understanding of how atmospheric polarization varies with aerosols, clouds, and surface reflectance, an all-sky polarization imager has been designed, built, calibrated, and operated in a variety of field experiments. This paper describes modifications made to that instrument to enable continuous, unattended outdoor operation. The primary modifications were development of a weather-proof housing and an automated sun occulter incorporating an on-board microcontroller that continually calculates solar position and moves an occulting disk on a thin metal band to prevent direct sunlight from falling on the polarimeter lens. This occulter is designed to not obstruct the principal scattering plane, defined as the plane containing the zenith, the Sun, and the observer.

We already implemented an imaging polarimeter able to capture at high-speed the full information about linear polarization of a monochromatic light beam (namely its first three Stokes parameters). The polarizing element was a single ferroelectric liquid crystal cell, acting as a half-wave plate (therefore as a polarization rotator) at its design wavelength. In this paper, we report the improvement of our system in order to grab the full Stokes information, including the fourth Stokes parameter. The procedure consists in two operations. First, optimally controlling our polarization component with an additional fourth voltage level. Second, shifting the wavelength operation in order to get benefit of the device chromatic behavior: away from its design wavelength, the device does not behave as a half-wave plate any longer, and with proper level control, the system matrix of our polarization state analyzer (consisting of the liquid crystal cell and of a fixed linear polarizer) can reach rank 4. Therefore, elliptical polarization can be fully analyzed, as it could be with a nematic liquid crystal device, but at a much higher frame rate. Results of operation at 200 fps are provided.

We have evaluated wire grid polarizers for the thermal infrared in the 3 to 12μm wavelength range. Wire grid structures are an effective means of producing infrared polarizers with short optical path and having large acceptance angles. Performance of two sets of polarizers manufactured by Moxtek, for the 3-5μm and 8-12μm wavelength ranges, were tested in a Mueller matrix spectropolarimeter and found to have transmission ratios on the order of 1000.

Meadowlark Optics has successfully built and demonstrated a liquid crystal based tunable filter with novel FWHM tunability. This allows separate control over both the location of a narrow spectral bandpass and the width of the bandpass function. This non-mechanical, imaging filter thus enables random access of the visible to near IR spectrum and also controlling the specificity of the transmitted light. We will discuss both the relative trade-offs in this filter design space and present data from functional units.

We present a novel imaging sensor capable of capturing the polarization properties of partially polarized light in high resolution and in real-time. The imaging sensor monolithically integrates aluminum nanowire optical filters with CCD imaging array to achieve a high resolution polarization imaging sensor. The CCD polarization image sensor is composed of 1000 by 1000 imaging elements with 7.4μm pixel pitch and has dynamic range of 65dB. The measured signal-to-noise ratio of the sensor is 45dB. The CCD array is covered with an array of pixel-pitch matched nanowire polarization filters with four different orientations offset by 45°. Raw polarization data is presented to a processing board at 40 frames per second, where intensity, degree and angle of polarization of the incident light are computed. The final polarization results are presented in false color representation.

Vector beams exhibit spatially inhomogeneous polarization. Here we show that this diversity of polarization in conjunction with specially designed optical setups can be used to parallelize the respective polarization state generation and detection processes in Mueller matrix polarimetry, which hitherto are done sequentially, limiting the speed with which samples can be characterized. Polarimetry based on these principles, that can extract twelve Mueller matrix elements from a single intensity image, is presented. Simulation results show that this form of polarimetry can be used to study a wide variety of samples such as magnetically active metamaterials.

We describe apparatus and methods to measure the sensitivity of arthropod eyes to wavelength and polarization. While these general methods are well-known in the retinography community, they are less familiar to the general optics community. Measurement of polarization sensitivity is particularly uncommon even among retinographers, and our research plan and example results are detailed.

In recent years there has been an increased interest in using polarimetric imaging sensors for terrestrial remote sensing applications because of their ability to discriminate manmade objects in a natural clutter background. However, adverse weather limits the performance of these sensors. Long Wave Infrared (LWIR) polarimetric sensor data of a scene containing manmade objects in a natural clutter background is compared with simultaneously collected environmental data. In this paper, a metric is constructed from the Stokes parameter S1 and is correlated with some environmental channels. There are differences in the correlation outputs, with the sensor data metric positively correlated with some environmental channels, negatively correlated with some channels and uncorrelated with other channels. Results from real data measurements are presented and interpreted. An uncooled LWIR sensor using an achromatic retarder to capture the polarimetric states performed the data collection. The environmental channels include various meteorological channels, radiation loading and soil properties.

Radiative transfer is commonly modeled as the propagation of unpolarized radiation. More accurate approaches utilizing polarimetric quantities are usually only applied to sensors that purposefully discriminate polarimetric information. In this paper, we examine the effect on fidelity of utilizing polarimetric radiative transfer modeling for non-polarimetric sensors. We show that if the primary irradiance on a scene is significantly polarized (such as sky irradiance) then polarimetric radiative transfer modeling is warranted and provides a significant increase in fidelity. We demonstrate this effect by performing target detection of shadowed man-made objects in real and simulated imagery.

Lidar bioaerosols discrimination based on depolarization signature is studied. The measurements were performed over 25 pollens and 2 dusts under controlled environment at a distance of 100 m, at wavelengths of 355 nm, 532 nm, 1064 nm and 1570 nm, and both linear and circular polarizations were used. It is found that discrimination of bioaerosols using single wavelength linear depolarization ratios is difficult because most of them are quite alike. However, two or more wavelengths measurements make it possible to discriminate different bioaerosols against others, especially when a depolarization ratio cumulative distribution is available.

Subsurface polarimetric (differential polarization, degree of polarization or Mueller matrix) imaging of various targets in turbid media shows image contrast enhancement compared with total intensity measurements. The image contrast depends on the target immersion depth and on both target and background medium optical properties, such as scattering coefficient, absorption coefficient and anisotropy. The differential polarization image contrast is usually not the same for circularly and linearly polarized light. With linearly and circularly polarized light we acquired the orthogonal state contrast (OSC) images of reflecting, scattering and absorbing targets. The targets were positioned at various depths within the container filled with polystyrene particle suspension in water. We also performed numerical Monte Carlo modelling of backscattering Mueller matrix images of the experimental set-up. Quite often the dimensions of container, its shape and optical properties of container walls are not reported for similar experiments and numerical simulations. However, we found, that depending on the photon transport mean free path in the scattering medium, the above mentioned parameters, as well as multiple target design could all be sources of significant systematic errors in the evaluation of polarimetric image contrast. Thus, proper design of experiment geometry is of prime importance in order to remove the sources of possible artefacts in the image contrast evaluation and to make a correct choice between linear and circular polarization of the light for better target detection.

We report the results of a diurnal study in which radiometrically calibrated polarimetric and conventional thermal imagery are recorded in the MidIR and LWIR to identify and compare the respective time periods in which minimum target contrast is achieved. The MidIR polarimetric sensor is based on a division-of-aperture approach and has a 640x512 InSb focal-plane array, while the LWIR polarimetric sensor uses a spinning achromatic retarder to perform the polarimetric filtering and has a 324x256 microbolometer focal-plane array. The images used in this study include the S0 and S1 Stokes images of a scene containing a military vehicle and the natural background. In addition, relevant meteorological parameters measured during the test period include air temperature, ambient loading in the LWIR, relative humidity, cloud cover, height, and density. The data shows that the chief factors affecting polarimetric contrast in both wavebands are the amount of thermal emission from the objects in the scene and the abundance of MidIR and LWIR sources in the optical background. In particular, it has been observed that the MidIR polarimetric contrast was positively correlated to the presence of MidIR sources in the optical background, while the LWIR polarimetric contrast was negatively correlated to the presence of LWIR sources in the optical background.

Detection and clearance of subsurface land mines has been one of the challenging humanitarian and military tasks. Passive polarization-based imagery has played important role achieving this task. This paper presents new fusion technique where polarization-based imagery is fused with traditional intensity imagery using high-boost approach. The main idea of the high-boost approach used in this paper is to give the polarization imagery obtained from the Stokes vector imagery more weight in forming the final fused image. It is shown that the proposed technique improves the recognition of surface land mines. This improvement is shown using correlation performance metrics derived from wavelet-filter joint-transform correlation algorithm used for pattern recognition.

Simulation of moving vehicle tracking has been demonstrated using hyperspectral and polarimetric imagery (HSI/PI). Synthetic HSI/PI image cubes of an urban scene containing moving vehicle content were generated using the Rochester Institute of Technology's Digital Imaging and Remote Sensing Image Generation (DIRSIG) Megascene #1 model. Video streams of sensor-reaching radiance frames collected from a virtual orbiting aerial platform's imaging sensor were used to test adaptive sensor designs in a target tracking application. A hybrid division-of-focal-plane imaging sensor boasting an array of 2×2 superpixels containing both micromirrors and micropolarizers was designed for co-registered HSI/PI aerial remote sensing. Pixel-sized aluminum wire-grid linear polarizers were designed and simulated to measure transmittance, extinction ratio, and diattenuation responses in the presence of an electric field. Wire-grid spacings of 500 [nm] and 80 [nm] were designed for lithographic deposition and etching processes. Both micromirror-relayed panchromatic imagery and micropolarizer-collected PI were orthorectified and then processed by Numerica Corporation's feature-aided target tracker to perform multimodal adaptive performance-driven sensing of moving vehicle targets. Hyperspectral responses of selected target pixels were measured using micromirror-commanded slits to bolster track performance. Unified end-to-end track performance case studies were completed using both panchromatic and degree of linear polarization sensor modes.