In the first part of this paper, we present a method to estimate the shape of transparent objects by using polarization. Few existing methods for this procedure consider internal interreflection, which is a multiple reflection occurring inside the transparent object. Our proposed method considers such interreflection by using the raytracing method. Also, we calculate the polarization state of the light using Mueller calculus. We then combine these methods to produce rendered polarization data. The shape of the object is computed by an iterative framework that minimizes the difference between the obtained polarization data and the rendered polarization data. In the second part of this paper, we present an apparatus to measure the polarization state of the light. To analyze the light, we use a material called PLZT whose material state changes with the applied voltage. We obtain the polarization state of the light by controlling the voltage of the PLZT from the computer. In the last part of this paper, we present some experimental results using the proposed method and apparatus.

We consider the problem of recovering a moving visual scene recorded through a semi-reflective device, and extend the Sparse Component Analysis (SCA) method to three-dimensional data sources, using two different mixtures of the dynamic image source and the superimposed reflection, recorded at different polarizations, without having any a-priori knowledge about the structure and/or the statistics of the sources, or of the mixing matrix. We first apply our method on a simple physical example of separation of dynamic reflections, such as video signals recorded through the windshield of a car. In this example the required assumptions of linearity and stationarity are valid. A more interesting application deals with dynamic scenarios recorded from aircrafts or satellites, where it is desirable to extract a clear landscape view by separating it from a thin semi-transparent layers of clouds superimposed on the desired dynamic image. This is a more complex problem, since the mixtures are not stationary in space and the mixing coefficients vary in the presence of clouds. Further, the mixtures are not strictly linear and involve also multiplicative and convolutive components. We apply the 3D-SCA method in simulations of linearly mixed moving landscape contaminated by clouds.

Recently, 3D models are used in many fields such as education, medical services, entertainment, art, digital archive, etc., because of the progress of computational time and demand for creating photorealistic virtual model is increasing for higher reality. In computer vision field, a number of techniques have been developed for creating the virtual model by observing the real object in computer vision field. In this paper, we propose the method for creating photorealistic virtual model by using laser range sensor and polarization based image capture system. We capture the range and color images of the object which is rotated on the rotary table. By using the reconstructed object shape and sequence of color images of the object, parameter of a reflection model are estimated in a robust manner. As a result, then, we can make photorealistic 3D model in consideration of surface reflection. The key point of the proposed method is that, first, the diffuse and specular reflection components are separated from the color image sequence, and then, reflectance parameters of each reflection component are estimated separately. In separation of reflection components, we use polarization filter. This approach enables estimation of reflectance properties of real objects whose surfaces show specularity as well as diffusely reflected lights. The recovered object shape and reflectance properties are then used for synthesizing object images with realistic shading effects under arbitrary illumination conditions.

Recent studies have shown that major visibility degradation effects caused by haze can be corrected for by analyzing polarization-filtered images. The analysis is based on the fact that the path-radiance in the atmosphere (airlight) is often partially polarized. Thus, associating polarization with path-radiance enables its removal, as well as compensation for atmospheric attenuation. However, prior implementations of this method suffered from several problems. First, they were based on mechanical polarizers, which are slow and rely on moving part. Second, the method had failed in image areas corresponding to specular objects, such as water bodies (lakes) and shiny construction materials (e.g., windows). The reason for this stems from the fact that specular objects reflect partially polarized light, confusing a naive association of polarization solely with path-radiance. Finally, prior implementations derived necessary polarization parameters by manually selecting reference points in the field of view. This human intervention is a drawback, since we would rather automate the process. In this paper, we report our most recent progress in the development of our visibility-improvement method. We show directions by which those problems can be overcome. Specifically, we added algorithmic steps which automatically extract the polarization parameters needed, and make visibility recovery more robust to polarization effects originating from specular objects. In addition, we now test an electrically-switchable polarizer based on a liquid crystal device for improving acquisition speed.

This paper will describe the evolution of the Marshall Space Flight Center's (MSFC) electro-optical polarimeter with emphasis on the field-of-view characteristics of the KD*P modulator. Understanding those characteristics was essential to the success of the MSFC solar vector magnetograph. The paper will show how the field-of-view errors of KD*P look similar to the linear polarization patterns seen in simple sunspots and why the placement of the KD*P in a collimated beam was essential in separating the instrumental polarization from the solar signal. Finally, this paper will describe a modulator design which minimizes those field-of-view errors.

A real-time measurement method for both birefringence dispersion and azimuthal angle is described. An optical set-up of this measurement consists of a white light source, two polarizers and two reterders without any rotation. A spectroscopic intensity is detected by a spectrometer. It is modulated with two different frequencies along wave number. Only the single spectroscopic intensity is sufficient to determine the retardation and the azimuthal angle with wavelength-dependence using two amplitude spectrum and phase by the fast Fourier transform method. A birefringence measurement of a Babinet-Soleil compensator as a sample is demonstrated experimentally.

A new technique for simultaneous multi-angle ellipsometric measurements of anisotropic optical structures such as films used in the display industry is introduced. A very small area on the sample is illuminated with a focused beam which after it interacts with the sample and is polarization analyzed is spread across a CCD. Each pixed collects light from a different angle incident on the sample allowing data collection at numerous incident angles simultaneously. The small but significant polarization aberrations of the microscope objectives provide a significant challenge to accurate measurement A mathematical description of the ellipsometric technique is presented. The optical properties of two biaxial samples, a stretched plastic retarder element used for correcting angle of incident effects in LC displays, and a thin layer of E-type polarizing dried liquid crystal material are measured and maps of the ellipsometric parameters Ψ and ▵ as a function incident and azimuthal angles are presented. Data from both samples are reduced using an iterative algorithm with a biaxial thin film modeling software package to compute all three principle components of the dielectric tensor as well as it's orientation.

Mueller matrix imaging polarimetry was used to study stress in a series of a high numerical aperture molded glass lenses. An interesting radially symmetric retardance was found which resembled the polarization aberration induced by coatings. Upon investigation the source of the polarization aberration is traced to a remarkably symmetric radial stress birefringence in the glass believed to arise during fire-polishing of the surfaces. While annealing the lenses relieves much of the stress birefringence, reducing the retardance of the lenses by a factor of five, the lenses remained unusable for critical polarization applications.

Polarization modulation in photo-elastic modulators (PEM) driven on and off resonance has been investigated for a commercially available PEM using a high speed infrared (lambda=1550 nm) polarimeter. Off-resonance operation was explored in the hope of finding a slower operating mode than the primary resonance. The primary resonance, used for normal PEM operation, was 5 Hz wide with a Q of 8500. The phase transfer function was well behaved and typical of electrical resonances. Device startup and shutdown had smooth amplitude changes occurring over 1/3rd of a second. The photo-elastic modulator was examined at drive frequencies significantly below the resonant frequency. Driving the PEM with several odd sub-harmonics generated resonance at the fundamental frequency. Three other lower frequency resonances were discovered, but all at an oscillation amplitude more than 12 db below the amplitude of the fundamental resonance. Thus a practical configuration to allow slower operation of the PEM was not found.

This paper describes the methodology and presents the results of the design of a polarization-sensitive system used to increase the signal-to-clutter ratio in a robust outdoor structured lighting sensor that uses standard CCD camera technology. This lighting sensor is intended to be used on an autonomous vehicle, looking down to the ground and horizontal to obstacles in an 8 foot range. The kinds of surfaces to be imaged are natural and man-made, such as asphalt, concrete, dirt and grass. The main problem for an outdoor eye-safe laser imaging system is that the reflected energy from background clutter tends to be brighter than the reflected laser energy. A narrow-band optical filter does not reduce significantly the background clutter in bright sunlight, and problems also occur when the surface is highly absorptive, like asphalt. Therefore, most of applications are limited to indoor and controlled outdoor conditions. A series of measurements was made for each of the materials studied in order to find the best configuration for the polarizing system and also to find out the potential improvement in the signal-to-clutter ratio (STC). This process was divided into three parts: characterization of the reflected sunlight, characterization of the reflected laser light, and measurement of the improvement in the STC. The results show that by using polarization properties it is possible to design an optical system that is able to increase the signal-to-clutter ratio from approximately 30% to 100% in the imaging system, depending on the kind of surface and on the incidence angle of the sunlight. The technique was also analyzed for indoor use, with the background clutter being the room illumination. For this specific case, polarization did not improve the signal-to-clutter ratio.

Range and sensitivities of lidar measurements are limited in daytime use by sky background noise (BGN). We report on a polarization technique to reduce the detected sky BGN by making use of the fact that daylight sky noise is polarized by atmospheric scattering to a greater or lesser degree, depending on the solar zenith angle. With suitable rotation of a beam polarizer at the entrance of the detector, the sky noise reaching the detector is minimized. At the same time, the polarization of the outgoing lidar signal is rotated to align the polarizations of both the outgoing and elastically scattered return signals with that of the polarizer in front of the detector. This ensures unhindered passage of lidar returns to the detector while at the same time minimizing detected BGN. Daylight measurements with a vertically oriented elastic backscatter lidar at 532 nanometers show that as much as tenfold improvements in signal to noise ratio (SNR), and consequent improvements in effective lidar range, can be obtained for high solar zenith angles (less for angles closer to the zenith) in typical urban atmospheric conditions. The variations in SNR as a function of different solar angles were found to be consistent with theoretical estimates of the variation of the polarization factor for incoming vertical skylight for an urban atmosphere based on adjacent CIMEL measurements of the atmospheric optical depth over the same period.

Information on local cloud coverage, with high spatial and temporal resolution, is useful for studying how the radiative properties of clouds affect the climate. The resolution of a lidar allows for detection of subvisual cloud and aerosol layers, and for determining particle sizes of the scatterers. A cloud lidar sensitive to polarization can distinguish between ice and water in clouds, since ice crystals are more depolarizing than water droplets. Cloud lidars complement either ground-based or space-based cloud imagers by supplying the missing vertical dimension. This paper describes the design and characterization of a lidar system for the direct detection of clouds, using a liquid crystal to discriminate between backscattered polarization states on alternate laser pulses (at 30 Hz). The source is a Nd:YAG laser at a wavelength of 532 nm and with pulse energies of 118 mJ. The system is designed to be compact and robust enough for transport and deployment. Data presented show the lidar system is capable of detecting clouds up to 9.5 km above ground level (the normal operating range is 15 km) with a 1.5 m range resolution. The receiver field of view is conveniently variable up to 8.8 mrad. Daytime operation is possible, thanks to laser-line interference filters and a gated photomultiplier tube. Polarization discrimination is sufficient to measure depolarization ratios with an additive error of less than 0.4%.

An instrument is described that operates as a true monostatic reflectometer. The instrument collects complete polarimetric information as well as reflectance. A beamsplitter at 45° to the incident and reflected beam allows monostatic operation. Complete polarimetric information in the form of Mueller matrices are measured by using a polarization state generator prior to the sample and a polarization state analyzer after reflection from the sample and beamsplitter. This Mueller matrix polarimeter is in the dual rotating retarder configuration. Two lasers currently serve as sources. The hardware and data reduction methods are discussed, and measurement results are given.

Active imaging polarimetry is a unique imaging technique in which a particular scene of interest is illuminated by a laser source with a known polarization state. Changes in the state of polarization of the received light yields information beyond what is available in conventional intensity imaging. This approach has an advantage over passive polarimetry in that one has control over the polarization state of the illumination with the potential of determining all sixteen elements of the associated Mueller matrix. While determining the entire Mueller matrix is the most comprehensive method for describing the polarization changing properties of the scene, for most cases it does not yield significantly more information than simply determining the 4 diagonal elements of the Mueller matrix. The Active Wollaston Polarimeter is based around the ability of the Wollaston prism to split orthogonal polarization states into two beams propagating at slightly different angles allowing two images to be formed on a single camera. The Wollaston prism, combined with a series of liquid crystal variable retarders allows monopulse determination of any single Mueller matrix element. This technique results in a fast, compact polarization measurement system. This paper presents the initial laboratory results of the Active Wollaston Polarimeter along with an analysis of the polarimeter's performance.

This paper will describe the Vacuum Ultraviolet (VUV) polarization testing of the Solar Ultraviolet Magnetograph (SUMI) optics. SUMI is being develop for a sounding rocket payload to prove the feasibility of making magnetic field measurements in the transition region. This paper will cover the polarization properties of the VUV calibration polarizers, the instrumental polarization of the VUV chamber, SUMI's toroidal varied-line-space gratings and the SUMI polarimeter.

On-orbit optical sensors are the primary data source for the remote sensing community. A rigorous pre-flight characterization and calibration is a key to the success of their mission. Indeed, preliminary calibration and correction factors are determined during this process. As part of this process, prior to the launch of NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) its polarization sensitivity was measured. In this work, our goal was to simulate these measurements using computer ray tracing software. Based on that, we could evaluate the evolution of the different coatings (Mirror, Beam splitters, Anti-reflection and Band pass filters) due to degradation over time. We were able to simulate the measurements and obtained what the theoretical polarization sensitivity should be. The results were compared to the pre-launch measurements and an analysis of the whole MODIS optical system was performed in order to explain these differences. A full description of the MODIS polarization ray tracing procedure along with a discussion on the results and their implications on past, present and future work will be given.

One of the most significant challenges in performing infrared (IR) polarimetery is the focal plane array (FPA) nonuniformity (NU) noise that is inherent in virtually all IR photodetector technologies that operate in the midwave IR (MWIR) or long-wave IR (LWIR). NU noise results from pixel-to-pixel variations in the repsonsivity of the photodetectors. This problem is especially severy in the microengineered IR FPA materials like HgCdTe and InSb, as well as in uncooled IR microbolometer sensors. Such problems are largely absent from Si based visible spectrum FPAs. The pixel response is usually a variable nonlinear response function, and even when the response is linearized over some range of temperatures, the gain and offset of the resulting response is usually highly variable. NU noise is normally corrected by applying a linear calibration to the data, but the resulting imagery still retains residual nonuniformity due to the nonlinearity of the photodetector responses. This residual nonuniformity is particularly troublesome for polarimeters because of the addition and subtraction operations that must be performed on the images in order to construct the Stokes parameters or other polarization products. In this paper we explore the impact of NU noise on full stokes and linear-polarization-only IR polarimeters. We compare the performance of division of time, division of amplitude, and division of array polarimeters in the presence of both NU and temporal noise, and assess the ability of calibration-based NU correction schemes to clean up the data.

A novel Monte Carlo simulation algorithm is presented for modeling the time evolution of diffuse light backscattering in a highly turbid medium. The computational approach is based on the Mie scattering theory and uses the Stokes vector-Mueller matrix formalism for simulating the polarized light propagation. We applied the algorithm to calculate a time sequence of 2D Mueller matrices (time resolved two-dimensional polarization patterns) characterizing the temporal evolution of a scattering process in a turbid medium. The generated time-resolved 2D Mueller matrices are compared to time-resolved 2D Mueller matrices obtained experimentally [1].

Several single-valued metrics have been introduced for the assessment of depolarization including the Depolarization Index and the Average Degree of Polarization (obtained by averaging the exiting degree of polarization over all incident polarization states). These metrics are compared then a more complete representation of depolarization is introduced, the Degree of Polarization Surfaces, which help elucidate the structure of the depolarization degrees of freedom within the Mueller calculus.

There is a growing interest toward using lidar for forest remote sensing. The Multiwavelength Airborne Polarimetric Lidar (MAPL) was designed primarily for vegetation remote sensing purposes. The system has full lidar waveform capture and polarimetric measurement capabilities at 532-nm and 1064-nm wavelengths. To study the polarimetric reflectance from different tree species, ground experiments were conducted using the MAPL system. Three tree canopies with distinct features were selected for this study. These are cottonwood (Populus deltoides), black willow (Salix nigra) and red-cedar (Juniperus virginiana). The test results revealed that the shapes of the lidar waveforms, the depolarization ratios, and the percent reflectance data all have distinct features for different tree species. The MAPL system is proved to be able to detect all these features. Our study indicates that the MAPL data have the potential to be used toward developing a tree species discrimination algorithm. In addition, it is also believed that these data can be used to detect tree stress conditions.

In this paper, performance bounds are computed for the estimation of the degree of polarization for reflected fields with active laser illumination. Bounds are compared for three situations: i) measurement and processing of the complex amplitude of two orthogonal field components; ii) measurement and processing of the intensity of two orthogonal field components; and iii) measurement and processing of the total intensity of the field.

A polarization-sensitive lidar was used to detect honeybees trained to locate buried landmines by smell. Lidar measurements of bee location agree reasonably well with maps of chemical plume strength and bee density determined by visual and video counts, indicating that the bees are preferentially located near the explosives and that the lidar identifies the locations of higher bee concentration. The co-polarized lidar backscatter signal is more effective than the cross-polarized signal for bee detection. Laboratory measurements show that the depolarization ratio of scattered light is near zero for bee wings and up to approximately thirty percent for bee bodies.

Although natural light sources produce depolarized light, patterns of partially linearly polarized light appear in the sky due to scattering from air molecules, dust, and aerosols. Many animals, including bees and ants, orient themselves to patterns of polarization that are present in daytime skies, when the intensity is high and skylight polarization is strong and predictable. The halicitid bee Megalopta genalis inhabits rainforests in Central America. Unlike typical bees, it forages before sunrise and after sunset, when light intensities under the forest canopy are very low, and must find its way to food sources and return to its nest in visually challenging circumstances. An important cue for the orientation could be patterns of polarization in the twilight sky. Therefore, we used a calibrated digital camera to image skylight polarization in an overhead patch of sky, 87.6° across, before dawn on Barro Colorado Island in Panama, where the bees are found. We simultaneously measured the spectral properties of polarized light in a cloudless patch of sky 15° across centered on the zenith. We also performed full-sky imaging of polarization before dawn and after dusk on Lizard Island in Australia, another tropical island. During twilight, celestial polarized light occurs in a wide band stretching perpendicular to the location of the hidden sun and reaching typical degrees of polarization near 80% at wavelengths >600 nm. This pattern appears about 45 minutes before local sunrise or disappears 45 minutes after local sunset (about 20 minutes after the onset of astronomical twilight at dawn, or before its end at dusk) and extends with little change through the entire twilight period. Such a strong and reliable orientation cue could be used for flight orientation by any animal with polarization sensitivity that navigates during twilight.

In the area of aerosol remote sensing, one of the more noteworthy points of the last decade has been the realization that dust and smoke can be sensed from space over land and ocean by utilizing observations of scattered ultraviolet light [Torres, et al. 1998]. The spectral contrast ratio available from the Total Ozone Mapping Spectrometer (TOMS) backscatter ultraviolet (buv) data does provide a wealth of qualitative information, such as the ability to track the global dispersion of dust and smoke from regional sources. Quantitative information, e.g. total optical depth, single scattering albedo, however, is more difficult to extract from buv data. Assumptions must be made concerning various parameters that influence buv observations, e.g. the height of the aerosol layer, surface albedo, aerosol size distribution and index of refraction. While the necessity of assumptions is due in part to the availability of only two wavelengths from historical TOMS data, these assumptions may not truly be needed for future sensors. We examine what can be gained from making measurements of polarization in addition to those of radiance (as is currently done by TOMS and its successor the Ozone Measuring Instrument, OMI, on EOS-AURA) in the TOMS spectral coverage range free from ozone absorption (340-380 nm). Measurements of the degree of linear polarization and the plane of polarization with an uncertainty of less than 0.005 would help to determine the aerosol layer height to within less than 1 km. Multi-angle measurements would also help to better utilize the polarization data by defining the particle effective radius.

Beetles of the scarab family have been found to reflect circularly polarized light from incident unpolarized light. There are many known animals that use polarized light in some form and several that actually create it, but there are few examples of the creation of circularly polarized light in nature. Previous work is summarized, and new measurements of several scarab specimens are presented.

Long-wave infrared (LWIR) imaging is a prominent and useful technique for remote sensing applications. Moreover, polarization imaging has been shown to provide additional information about the imaged scene. However, polarization estimation requires that multiple measurements be made of each observed scene point under optically different conditions. This challenging measurement strategy makes the polarization estimates prone to error. The sources of this error differ depending upon the type of measurement scheme used. In this paper, we examine one particular measurement scheme, namely, a simultaneous multiple-measurement imaging polarimeter (SIP) using a microgrid polarizer array. The imager is composed of a microgrid polarizer masking a LWIR HgCdTe focal plane array (operating at 8.3-9.3 μm), and is able to make simultaneous modulated scene measurements. In this paper we present an analytical model that is used to predict the performance of the system in order to help interpret real results. This model is radiometrically accurate and accounts for the temperature of the camera system optics, spatial nonuniformity and drift, optical resolution and other sources of noise. This model is then used in simulation to validate it against laboratory measurements. The precision and accuracy of the SIP instrument is then studied.

Imaging polarimetry has the potential to be a key sensor technology in a number of target detection applications. Imaging polarimeters measure the polarization state of light emitted from and/or reflected from scenes. The light is polarized because of the geometry, roughness and material properties of the objects embedded in the scene. This added information enhances conventional intensity and color imagery, potentially surpassing its performance in low contrast situations. In this paper, we describe a divided aperture MWIR imaging polarimeter which acquires multiple polarization images simultaneously. At the heart of the polarimeter is a relay lens set that produces four identical images on a single focal plane array from a single aperture. Each of the four images measures a different orientation of linear polarization, 0, 45, 90 and 135 degrees. The relay lens set operates inside of a pour fill Dewar of a InSb MWIR camera. The design and calibration method for the polarimeter are given along with example data sets taken from the air over Huntsville, AL.

In our laboratory we built a Stokes polarimeter using two photoelastic modulators (PEMs). We applied two different signal processing methods to this dual PEM Stokes polarimeter. In one method, we used lock-in amplifiers to measure the PEM modulated signals. In the other method, we used Fourier analysis of a digitized waveform that contains the modulated signals. The dual PEM Stokes polarimeter can measure all normalized Stokes parameters. In this paper we present and compare results obtained using both signal processing methods. We discuss how each method benefits selected applications of the dual PEM Stokes polarimeter.

Polarimetry has been shown to aid in target detection by improving target contrast against both background and clutter. Further, Stokes vector sensors can provide surface orientation and material data, and permit extraction of targets obscured by scattering in the observer to object atmospheric column. This report presents a discussion of the construction of, and data from, the BATC imaging Stokes polarimeter. The polarimeter employs electro-optic modulators to acquire full Stokes vector image sets at a cadence sufficient to freeze target and background motion. These images are co-added to produce the polarimetric SNR necessary to fulfill mission requirements. We discuss the relationship of image timing, integration time, and SNR in the context of specific objectives for the polarimetric products. The relative advantages of implementing different electro-optic technologies will be illustrated by test and field image data.

In this paper we show how measurements made by a simple handheld polarimeter in conjunction with automated sunsky radiometers can be used to effectively constrain the real part of the complex refractive index of aerosols. We find that even measurements over a limited angular range near 90° scattering angle are sufficient for this purpose. We also note that because of the effect of surface reflectance on the observed degree of linear polarization (DOLP) it is sensible to select spectral bands for these measurements for which the surface is relatively dark and homogeneous (i.e. wavelengths shorter than 700 nm are to be preferred).

We present the first visible-spectrum snapshot imaging spectro-polarimeter based on a Computed Tomographic Imaging Spectrometer (CTIS). Improvements to our calibration methods have provided advances in the CTIS spectral resolution and in noise suppression which obstructed previous attempts to construct such an instrument. The resulting device is capable of 75×75 spatial resolution, 1 nm spectral resolution across the visible spectrum (400 nm-720 nm), at video frame rates. The instrument is also capable of complete Stokes vector polarimetry at a reduced spectral resolution (~10 nm).

A novel design of the channeled spectropolarimeter suited for stable operation is presented. An integrated polarization analyzing optics made of calcite is used together with a novel signal processing procedure to add the self-recalibration feature to the channeled spectropolarimeter. The recalibration of the system parameters and the measurement of the state of polarization are made simultaneously using only the light under measurement. A multi-channel spectrometer is also employed to avoid the errors associated with the wavelength-axis drift. Elimination of the thermal disturbance is demonstrated experimentally.

Polarization signatures of ground-based objects depend upon both the physical characteristics of the object and the polarization of the incident light. Models of polarization can accurately represent the polarization of incident light for clear skies, but the effect of cloudy skies upon object signatures is more difficult to predict. In response to the need for measurements to characterize the effect of variable sky polarization on target polarimetry, a multispectral visible band polarimeter (440 - 710 nm) has been developed. This polarimeter quickly changes to measure both full sky polarization and narrow field-of-view target signatures. Sky polarization is measured with a fisheye lens. Target polarization is measured with a 300 mm telephoto lens. A Liquid Crystal Variable Retarder (LCVR) design has been selected that uses two Meadowlark LCVR-300 variable retarders at set rotation angles. Current calibration work involves the removal of the fisheye effects on the Stokes vector. Future measurements will be used for validation of Polarized MODTRAN.

The increasing availability of multispectral, hyperspectral, and multisensor imagery during the past decade has motivated rapid growth in image fusion research for remote sensing application. While it is generally the goal of image fusion methods to obtain more information fiom the combination of multiple images than could be obtained from individual images, the measure of how well fused images actually achieve this goal is still largely subjective. Furthermore, in the selection of image data, and the analytical procedures to process this data, we make a sequence of implicit assumptions that need to be reviewed. Metrics are used to specify image characteristics necessary to perform specified tasks. New metrics are necessary to characterize the performance of image fusion techniques and also to determine the extent to which these techniques may provide more useful information than could be derived fiom non-fused imagery. Without metics, we cannot predict what data we need, or how to collect and to analyze it. There is currently no metric that encompasses both spatial and spectral resolution characteristics. A metric describing the quality of polarimetric imagery is an example of the larger problem of metrics required to specify the necessary characteristics of fused, multidimensional image data. Since polarimetric imagery is based upon the differences of image pairs obtained with the polarizer oriented orthogonally about the optic axis, misregistration introduces a false clutter that degrades information content of polarimetric imagery, so that a polarimetric image characteristic will depend upon registration accuracy. A General Image Quality Equation (GIQE) is a multivariate regression of the image quality metric against the independent imaging ammeters, such as registration in the case of polarimetric imagery. We need a General Image Quality Equation (GIQE) for polarimetric images in which one regression term describes misregistration. We need image quality metrics for polarimetric, multi-dimensional and fused multidimensional image data. In this paper we shall consider what metrics are needed to design and collect data, what general principles should guide the collection of analysis of data, and we shall consider polarimetric imagery as a simple example of a type of image fusion and analysis.

In previous work we showed that polarization-enhancement/encoding imagery can effectively be used to improve the detection and discrimination of targets. In this paper, we present a design and analysis of a new synthetic discriminant function for rotation/scale invariant for this polarization imagery system. Performance comparison between the proposed SDF and SDF obtained in traditional methods is included.

Data from a recent "first-look" at using Long Wave InfraRed Imaging Polarimetry (LWIR-IP) to detect surface swimmers is presented and discussed. A significant increase in detection SNR over conventional IR imaging techniques was discovered. The physical phenomena that produces the increased SNR is discussed along with data that shows range effects and their degradation on the SNR. Most significantly, a method to classify the detected object using the same dataset is discussed. Augmenting current swimmer detection systems using this technique will likely significantly decrease the false alarm rates of the system, thus saving manpower resources and preserving force readiness.

Passive polarization based imaging is a useful tool in computer vision and pattern recognition. A passive polarization imaging system forms a polarimetric image from the reflection of ambient light that contains useful information for computer vision tasks such as object detection (classification) and recognition. Applications of polarization based pattern recognition include material classification and automatic shape recognition. In this paper, we present two target detection algorithms for images captured by a passive polarimetric imaging system. The proposed detection algorithms are based on Bayesian decision theory. In these approaches, an object can belong to one of any given number classes and classification involves making decisions that minimize the average probability of making incorrect decisions. This minimum is achieved by assigning an object to the class that maximizes the a posteriori probability. Computing a posteriori probabilities requires estimates of class conditional probability density functions (likelihoods) and prior probabilities. A Probabilistic neural network (PNN), which is a nonparametric method that can compute Bayes optimal boundaries, and a -nearest neighbor (KNN) classifier, is used for density estimation and classification. The proposed algorithms are applied to polarimetric image data gathered in the laboratory with a liquid crystal-based system. The experimental results validate the effectiveness of the above algorithms for target detection from polarimetric data.

The use of polarized photons in cryptography holds the promise of secure cryptographic quantum key distribution schemes. In theory, quantum key distribution provides a key with unconditional security. In practice, however, the implemented schemes are often operated in a regime which excludes unconditional security, or even in a regime in which insecurity can be proven. We shall describe here the basics of quantum key distribution, provide an overview of the main ideas that lead to a proof of its unconditional security, and discuss the insecurity of practical quantum key distribution to long distances. The above review will be undertaken with a special emphasis on the role of the polarization of photons. Finally, we shall briefly touch on the importance of photons and their polarization degree of freedom in recent proposals for small-scale optical quantum computing.

Model calculations have been done on 3-dimensional objects. The descriptions of the objects are in terms of facets that make it possible to use ray tracing geometrical optics as a technique to calculate the scattering from the objects. The Bidirectional Reflectance Distribution Function (BRDF) for different polarization states have been used to describe the reflectance at a certain facet. By using Monte Carlo calculations, the scattering from all the facet surfaces of the object is added to a total reflectance. Thus the total reflectance has been obtained for different polarization states and for different angles of reflectance throughout the whole scattering hemisphere. The model has been applied to rough surfaces of color and polarization contrast measures, for example the Degree Of Linear Polarization, has been calculated. Also, a simple background has been applied, in order to obtain contrast measures between the object and the background. Comparison is made with field measurements of a military vehicle.

The registration of the reflected radiation polarization at the remote sensing allows gaining all the information available to optical methods about the observed object. Mathematically it gives a boundary-value problem of the vectorial radiative transfer equation (VRTE). The natural media of the radiative transfer have strongly anisotropic light scattering. Because of their singularities the solution of the boundary-value problem of VRTE for such media is a mathematically illconditioned problem. The classical method (S.Chandrasekhar) of the elimination of this problem is based on the subtraction of the nonscattered component from the solution. However under the conditions of strong anisotropy a diffusion part is not distinguished enough from the nonscattered part that gives heavy oscillations in the numerical solution. In this paper it is offered to subtract from the required solution of VRTE its solution in a small angle approximation (SAA), which besides nonscattered component contains all the anisotropic part. The rest of the solution is a smooth function, which can be easily found by any numerical method. As SAA it is offered to take a small angle modification of a spherical harmonics method (MSH), presenting the generalization of Goudsmit-Saunderson's solution for the case of VRTE.

An electrically controllable radial birefringent pupil filter is proposed in this paper. It consists of two polarizers and an improved electrically controllable optical azimuth rotator which has two λ/4 retarders, one electro-optical element and one radial birefringent crystal. Evolution and distribution of polarization states of this pupil filter is discussed. The most interesting and useful advantage of such a structure is that characteristic of intensity distribution near focus can be obtained merely controlling the applied-voltage for optimal electrical inductive phase difference Γ of the electro-optical element and azimuth angle of radial birefringent crystal. And the Γ zones are given where transverse superresolution and extended focal depth or focal shift can simultaneously be obtained.

Body parts that can reflect highly polarized light have been found in several species of stomatopod crustaceans (mantis shrimps). These polarized light reflectors can be grossly divided into two major types. The first type, usually red or pink in color to the human visual system, is located within an animal's cuticle. Reflectors of the second type, showing iridescent blue, are located beneath the exoskeleton and thus are unaffected by the molt cycle. We used reflection spectropolarimetry and transmission electron microscopy (TEM) to study the reflective properties and the structures that reflect highly polarized light in stomatopods. For the first type of reflector, the degree of polarization usually changes dramatically, from less than 20% to over 70%, with a change in viewing angle. TEM examination indicates that the polarization reflection is generated by multilayer thin-film interference. The second type of reflector, the blue colored ones, reflects highly polarized light to all viewing angles. However, these reflectors show a slight chromatic change with different viewing angles. TEM sections have revealed that streams of oval-shaped vesicles might be responsible for the production of the polarized light reflection. In all the reflectors we have examined so far, the reflected light is always maximally polarized at around 500 nm, which is close to the wavelength best transmitted by sea water. This suggests that the polarized light reflectors found in stomatopods are well adapted to the underwater environment. We also found that most reflectors produce polarized light with a horizontal e-vector. How these polarized light reflectors are used in stomatopod signaling remains unknown.

We first demonstrated that an organic electroluminescence (EL) device based on conjugated polymers, which emitted polarized light, aligned by ion beam processed films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Such devices would be particularly useful as backlights for conventional LCDs. Homogenous alignment of 4,4'-Bis[2-9(-ethyl-3-carbazoyl)vinylenyl]-1,1'-biphenyl (BECVB) films on thin layers of ion-beam-processed or rubbed PEDOT:PSS allows the construction of light-emitting diodes that emit polarized blue light (λ_em = 455 nm). The ion-beam-processed or rubbed PEDOT:PSS acts as an effective hole-injecting alignment layer. Polarized photoluminescence spectra demonstrated that the long axis of BECVB molecule was oriented along the ion-beam or rubbing direction. Owing to the orientation of BECVB molecules, polarized EL in the rubbing or ion-beam direction was observed in the device. The maximum photoluminescence polarization ratios of 5.6:1 and 3.2:1 were achieved for the devices aligned by rubbing and ion-beam methods, respectively.

In general, the state of polarization fluctuates randomly in the long fiber transmission system due to the surrounding temperature variation or external force on the fiber. The environmental influences, for example changes in stress and disturbance of water wave are more apparently under water. Consequently, to obtain the effective state of polarization stabilization method of transmission fiber becomes more and more important before achieving a under water remote polarization sensing system. In this paper, we use our homemade compensator to reduce the impact on the state of polarization (SOP) to and experimentally measure the polarization characteristics in underwater sensing. An effective polarization compensation apparatus is demonstrated in this paper. The stabilization of the polarization fluctuation is also achieved with applying our homemade compensator. Our experimental contributions can help the remote polarization signal transmission between land and under water.

Radar Shape From Shading (SFS) has been an active research topic on the processing of airborne and spaceborne single polarized SAR images during last two decades. The second generation of spaceborne SAR systems, such as Radarsat-2, will obtain fully polarized information about the ground targets. As the quadrature polarized (quad-pol) SAR images provide useful information on surface roughness and backscatter properties, this research intends to apply the SFS technique to the quad-pol SAR image to obtain topographic information. The technique is tested on the Canadian C/X-SAR (carried on Convair-580) quad-pol data, which is used as simulated sample data of potential Radarsat 2. The results (elevation profiles) are validated with the ground truth elevation profiles, generated from Digital Elevation Model of the area. The geometric accuracies are analyzed.

Spectral response of lateral optical anisotropy of periodic undoped type-II ZnSe/BeTe heterostructures with nonequivalent interfaces has been studied by spectroscopic ellipsometry. The spectra revealed two types of features corresponding to optical transitions with energies lying in the bandgap. The position of features of the first type does not depend on the heterostructure period. Features of the second type shift toward lower energies with decreasing period of the heterostructure. This behavior is explained in terms of a model taking into account the existence of electronic and hole interface states, as well as of a mixed-type interface state.

The main goal of the present paper is an answer the question how one have exactly to measure the Mueller matrix elements and what characteristics the polarimeter must have for the determination of anisotropy of the studied medium with minimal error and time of measurement.

The photoelastic modulator (PEM) is a resonant polarization modulator. It operates at the resonant frequency of a desired mechanical vibration mode of its optical element. The PEM is made of isotropic optical materials, in contrast to the birefringent materials used in electro-optic modulators. These two characteristics, operation at resonance and the use of isotropic optical materials, give the PEM unique optical properties, such as high modulation purity and efficiency, broad spectral range, high power handling capability, large acceptance angle, large useful aperture and good retardation stability. These properties make the PEM an effective polarization modulator in a variety of high sensitivity applications. In this first paper in a series, we focus on studying two basic optical properties of the PEM: useful aperture and acceptance angle.

An analytic mathematical model is developed for a Liquid Crystal Variable Retarder (LCVR) based on an extended Jones matrix representation. The model is used to determine the polarimetric response of the LCVR to rays of non-normal incidence. The model shows reasonable agreement with laboratory measurements of a LCVR for both linear and circular input polarizations at arbitrary incident angles. The model is also applied to a two-LCVR imaging polarimeter system that is capable of measuring the full Stokes parameters of a scene. It is shown that the LCVR response can have a significant effect on the recovered Stokes values for non-normal incidence, which is important for determining the polarimetric performance of such a system over an extended field-of-view.

Existing polarization imaging cameras typically use a set of sequential measurements and involve some physical motion of optical elements or changes in a liquid crystal element. In this paper, we present a spatially parallel polarization measurement approach that is designed to give measurements in real time. The idea is to use a group of 2×2 detectors where each detector responds to a different polarization. The signals from the detectors are sent to a digital processing unit where polarization parameters of interest are calculated in real-time. A laboratory prototype is presented that uses a quad-cell photodiode detector array with different polarizing elements placed over each detector. The signals from the detector elements are sent through amplifiers to A/D converters and then into a Field Programmable Gate Array (FPGA). This high-performance processing unit calculates various parameters such as degree of polarization and partial polarization. As the processing unit is fast, real-time operation is possible. Arrays of 2×2 groups will ultimately be required for image sensing.

There has been significant recent interest in the optimization of polarimeter systems, especially those designed for the remote sensing of polarization imagery. These studies have been motivated by a desire to improve the signal-to-noise-ratio (SNR) and the performance of the polarimeter in the presence of systematic calibration errors. These studies have been largely theoretical, and have not presented much experimental evidence of the theoretical predictions. In this paper, we present the design of an automated polarization characterization system that we use to test the theoretical hypothesis about the optimization of polarimeters. We present results here for rotating retarder polarimeters, and verify that quarter waveplates are not the optimum retarders to use in the presence of error and noise. Our results agree with predictions, but we find that the relative balance between noise and error is delicate.

We have previously shown that polarization enhancement of fingerprint images during the enrolment process improves the performance of the verification and identification processes. In this paper, we present a design and analysis of a new synthetic discriminant function (SDF) for rotation/scale invariant polarization-enhanced fingerprint system. Performance comparison between the proposed SDF and an SDF obtained for traditional fingerprint systems is included.