This PDF file contains the front matter associated with SPIE Proceedings Volume 8160, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The LWIR microgrid Polarized InfraRed Advanced Tactical Experiment (PIRATE) sensor was used to image several types of RC model aircraft at varying ranges and speeds under different background conditions. The data were calibrated and preprocessed using recently developed microgrid processing algorithms prior to estimation of the thermal (s₀) and polarimetric (s₁ and s₂) Stokes vector images. The data were then analyzed to assess the utility of polarimetric information when the thermal s0 data is augmented with s₁ and s₂ information for several model aircraft detection and tracking scenarios. Multi-variate analysis tools were applied in conjunction with multi-hypothesis detection schemes to assess detection performance of the aircraft under different background clutter conditions. We find that polarization is able to improve detection performance when compared with the corresponding thermal data in nearly all cases. A tracking algorithm was applied to a sequence of s₀ and corresponding degree of linear polarization (DoLP) images. An initial assessment was performed to determine whether polarization information can provide additional utility in these tracking scenarios.

Non-uniformity noise is common in infrared imagers, and is usually corrected through calibration, often by momentarily blocking the optical system with a relatively uniform temperature plate. The non-uniformity patterns also tend to drift and require periodic recalibration, necessitating occasional loss of video from the imager during the recalibration process. Microgrid polarimeters are especially sensitive to fixed-pattern noise because the polarization signal is acquired by differentiation of neighboring pixels. Scene-based algorithms attempt to alleviate the need for recalibration of the imager through image processing techniques. We introduce a new frequency-domain scene-based non-uniformity estimation and correction technique, and apply the technique to infrared and microgrid polarimeter imagery. The technique demonstrates promising results for shutter-assisted (recalibration) video, for microgrid polarization systems as well as most spatially modulated sensor systems.

Division-of-focal-plane (DoFP) polarimeters for the visible spectrum hold the promise of being able to capture both the angle and degree of linear polarization in real-time and at high spatial resolution. These sensors are realized by monolithic integration of CCD imaging elements with metallic nanowire polarization filter arrays at the focal plane of the sensor. These sensors capture large amounts of raw polarization data and present unique computational challenges as they aim to provide polarimetric information at high spatial and temporal resolutions. The image processing pipeline in a typical DoFP polarimeter is: per-pixel calibration, interpolation of the four sub-sampled polarization pixels, Stokes parameter estimation, angle and degree of linear polarization estimation, and conversion from polarization domain to color space for display purposes. The entire image processing pipeline must operate at the same frame rate as the CCD polarization imaging sensor (40 frames per second) or higher in order to enable real-time extraction of the polarization properties from the imaged environment. To achieve the necessary frame rate, we have implemented and evaluated the image processing pipeline on three different platforms: general purpose CPU, graphics processing unit (GPU), and an embedded FPGA. The computational throughput, power consumption, precision and physical limitations of the implementations on each platform are described in detail and experimental data is provided.

Surveillance operations and search and rescue missions regularly exploit electro-optic imaging systems to detect targets of interest in both the civilian and military communities. By incorporating the polarization of light as supplementary information to such electro-optic imaging systems, it is possible to increase their target discrimination capabilities, considering that man-made objects are known to depolarized light in different manner than natural backgrounds. As it is known that electro-magnetic radiation emitted and reflected from a smooth surface observed near a grazing angle becomes partially polarized in the visible and infrared wavelength bands, additional information about the shape, roughness, shading, and surface temperatures of difficult targets can be extracted by processing effectively such reflected/emitted polarized signatures. This paper presents a set of polarimetric image processing algorithms devised to extract meaningful information from a broad range of man-made objects. Passive polarimetric signatures are acquired in the visible, shortwave infrared, midwave infrared, and longwave infrared bands using a fully automated imaging system developed at DRDC Valcartier. A fusion algorithm is used to enable the discrimination of some objects lying in shadowed areas. Performance metrics, derived from the computed Stokes parameters, characterize the degree of polarization of man-made objects. Field experiments conducted during winter and summer time demonstrate: 1) the utility of the imaging system to collect polarized signatures of different objects in the visible and infrared spectral bands, and 2) the enhanced performance of target discrimination and fusion algorithms to exploit the polarized signatures of man-made objects against cluttered backgrounds.

Imaging polarimeters have currently and historically been largely used for remote sensing tasks. They have also been used to evaluate the defects and calibrate the polarization of liquid crystal displays. A particular type of polarimeter that has a great deal of unrealized potential is the microgrid array linear Stokes polarimeter. This type of polarimeter is not often used because of reconstruction errors. If these errors could be minimized, or mitigated via proper algorithmic reconstruction, then they have advantages over other types of polarimeters, mainly calibration (not much is needed) and proper operation over wide wavelength bands (due to the use of wire grid linear polarizers). In the paper I analyze the imaging equation of the microgrid Stokes polarimeter, using the full vectorial electric field.

Passive polarimetery has been used for many different remote sensing applications and can provide useful signatures for certain types of phenomenology. While broadband polarimeters have many advantages, such as high signal-to-noise ratio and small ground sample distance, there has been growing interest in the development of algorithms that take advantage of both spectral and polarimetric signals. The Multispectral Aerial Passive Polarimeter System (MAPPS) aims to produce multispectral polarimetric imagery of test scenes that can be used in algorithm development efforts and phenomenology studies. Preliminary data is presented along with a calibration and processing workflow that produces registered spectral Stokes imagery.

In 2009, we presented a compact division of amplitude imaging polarimeter design that captures the complete Stokes parameters simultaneously. The advantages of this design are 1) reduced sensitivity to noise based on the optimized selection of polarization elements, 2) minimization of differential aberrations in the four polarimetric channels, and 3) reduction in image registration errors. A prototype polarimeter was integrated for the near-infrared wavelength, field tested, and shown to calculate and display estimated scene polarization in real time. In this paper, several data sets are presented showing the instruments unique remote detection capabilities from various platforms and scene types. Acquisitions include ground view, aerial view of an urban area, and K-model rocket plume imaging at 2.5 kilometers. The acquisitions were processed using several new polarimetric imaging techniques detailing the unique remote detection capability. This polarimeter design was driven by the requirement to increase the accuracy of Stokes estimation. Therefore, this paper will conclude with the precision or an estimate of errors associated with this particular instrument.

Although different approaches to model a polarimeter's accuracy have been described before, a complete error budgeting tool for polarimetric systems has not been yet developed. Based on the framework introduced by Keller & Snik, in 2009, we have developed the M&m's code as a first attempt to obtain a generic tool to model the performance and accuracy of a given polarimeter, including all the potential error contributions and their dependencies on physical parameters. The main goal of the code is to provide insight on the combined influence of many polarization errors on the polarimetric accuracy of any polarimetric instrument. In this work we present the mathematics and physics based on which the code is developed as well as its general structure and operational scheme. Discussion of the advantages of the M&m's approach to error budgeting and polarimetric performance simulation is carried out and a brief outlook of further development of the code is also given.

We measure the Mueller matrix bidirectional reflectance distribution function (BRDF) of pressed and sintered powdered polytetrafluoroethylene (PTFE) reflectance standards for an incident angle of 75°. Rotationallyaveraged Mueller matrices from the materials showed a small asymmetry M₁₂ ≠ M₂₁ and M₃₄ ≠ -M₄₃ in the in-plane geometry. This asymmetry, however, followed Helmholtz reciprocity rules. A significant anisotropy was observed in the sintered samples, which was manifested as non-zero off-block diagonal elements that depended upon rotation of the samples. Modeling using a Mueller matrix extension to the radiative transfer equation was performed. While there was not quantitative agreement, some aspects of the data were observed, including the asymmetry. Availability of an improved Mueller matrix phase function should improve the quality of the model-experiment agreement.

The Stokes parameters of scattering from diffuse glass plates were measured and analyzed as a function a virtual scattering angle and a longitude scattering angle. Both of these scattering angles are defined for the facet model. The facet model for scattering from a diffuse surface predicts the polarization states of scattering quite well. The method and results of this analysis have a significant impact on the application of light scattering to the inspection and processevaluation industry, material science, etc.

Observed polarization and radiance images from a ground-based full-sky polarimeter are compared against a Successive Order of Scattering (SOS) radiative transfer model for July 2011 cloud-free days in Bozeman, Montana, USA. The imaging polarimeter measures radiance and polarization in 10-nm bands centered at 450, 490, 530, 675, and 780 nm. The AERONET-retrieved aerosol optical depth, size distribution, and refractive index are used as inputs to the SOS model. MISR BRDF retrievals are used for the surface reflectance. As shown in a previous work1 that considered 2009 data, model results generally agree with observation, but the simulated degree of polarization is typically higher than observed data. Potential sources of this difference are considered, especially errors in the AERONET-retrieved aerosol real refractive index.

Measurements of light intensity, often from space borne sensors, have been used to investigate the optical properties of the constituents of Earth's ecosystem. In ocean color research, water-leaving radiance can give useful information about inherent optical properties (IOPs). Additional consideration of polarization of the water-leaving radiance can lead to a better understanding of the physical and optical characteristics of the water body. Polarization properties strongly depend on particle microphysics, such as refractive index, effective radius, size distribution, and single scattering albedo. Using radiative transfer simulations of the polarized light field for various ranges of water constituents, we were able to develop relationships between the degree of polarization (DOP) and the ratio of hydrosol absorption to attenuation coefficient. This relationship was then studied for different viewing geometries of the polarized light and for different sun positions. A Neural Network sensitivity analysis was also performed to better understand the dependence of DOP on microphysical parameters.

On 5 February 2009 a colorful corona was observed when the Moon passed behind a thin wave cloud in Bozeman, Montana, USA. A dual-polarization lidar was used to determine that the diffracting particles were ice crystals, not the usually assumed liquid water droplets. Fraunhofer diffraction theory was used to estimate that the ice crystal effective diameter was 14.6 μm, much smaller than conventional ice crystals. The corona-producing cloud produced a lidar crosspolarization ratio of 0.4, confirming the presence of ice. The corona-producing cloud was located 9.5 km above mean sea level with air temperature near -60°C, thereby thermodynamically ruling out liquid water as well.

The use of optical metrology techniques for process control is now widespread. These techniques are fast and nondestructive, allowing higher throughputs than non-optical techniques like electron microscopies or AFM. We present here new developments using complete Mueller polarimetry in the back focal plane of a microscope objective to characterize overlay for microelectronic industry. Based on fundamental symmetries in the physics of periodic structures and polarized light and redundancies in the angle-resolved Mueller images we define estimators which vary linearly with the overlay. As a result, overlay measurement is sensitive to both the direction and sign of the overlay, and it does not require any detailed modeling of the target structures, provided two independent targets with known overlay values are available in close locations on the wafer. Realistic simulations on optimized structures suggest that accuracies in the order of 1 or 2 nm or better should be achievable. Moreover, with high NA objectives the proposed technique can be implemented with targets with lateral sizes as small as a few μm. Experimental results of both grating line profiles and overlay determinations will be presented. The samples, elaborated at LETI, have been accurately characterized by optical imaging AIM techniques and state-of-the-art AFM. The latest developments on the device itself as well as the advantages, possibilities and limitations of this new metrology technique will be discussed.

Recently, a polarimetric data reduction technique has been developed that in the presence of a time varying signals and noise free measurement process can achieve an error free reconstruction provided that the signal was band limited. Error free reconstruction for such a signal is not possible using conventional data reduction methods. The new approach provides insight for processing arbitrary modulation schemes in space, time, and wavelength. Theory predicts that a polarimeter that employs a spatio-temporal modulation scheme may be able to use the high temporal resolution of a spatially modulated device combined with the high spatial resolution of a temporally modulated system to attain greater combined resolution capabilities than either modulation on scheme can produce alone. A polarimeter that contains both spatial and temporal modulation can be constructed (for example) by placing a rotating retarder in front of a micropolarizer array (microgrid). This study develops theory and analysis for the rotating retarder microgrid polarimeter to show how the available bandwidth for each channel is affected by additional dimensions of modulation and demonstrates a working polarimeter with a simulation of Stokes parameters that are band limited in both space and time with a noisy measurement process.

Vehicle tracking is an integral component in layered sensing exploitation applications. The utilization of a combination of sensing modalities and processing techniques provides better insight about a situation than can be achieved with a single sensing modality. In this work, several robust features are explored for vehicle tracking using data captured in a remote sensing setting. A target area is surveyed by a sensor operating capturing polarization information in the longwave infrared (LWIR) band. We here extend our previous work ([1]) to experimental analysis of several feature sets including three classic features (Stokes images, DoLP, the Degree of Linear Polarization, and AoP, the Angle of Polarization) and several geometry inspired features.¹

For any kind of imaging polarimeter, at least four intensity images, named polarization state images, are needed to compute one full Stokes vector. When the polarimeter is designed according to the division-of-time principle, polarization state images are acquired sequentially. Consequently, the main issue is the systematic occurrence of artifacts as the scene is not static. Even though this is well known, little research has been done on this subject. Here a two-step motion-compensation-based method is proposed to fix it. The first step consists in estimating the motion between each image acquired according to the same polarization state. Then each image is warped according to a fraction of the previously estimated motion. Due to their dense and accurately estimated motion field we have shown optical-flow techniques to be the most efficient for motion-estimation in this case. Compensating the motion using optical flow to estimate it actually leads to a strong correlation criterion between corrected and reference polarization images. Our method allows the estimation of the polarization by post-processing the polarization state image sequence. It leads to a good estimation quality whether the scene is static or not, thus fixing the main issue of a divisionof- time polarimeter.

It is understood that Long Wave Infrared (LWIR) polarimetric imagery has the potential for detecting man-made objects in natural clutter backgrounds. Unlike Spectral and conventional broadband, polarimetric imagery takes advantage of the polarized signals emitted by the smooth surfaces of man-made materials. Studying the effect of how meteorological conditions affect polarization signals is imperative in order to understand where and how polarimetric technology can be beneficial to the war fighter. In this paper we intend to demonstrate the effects of weather on the performance of Stokes vector components, S₀, S₁, S₂, and the Degree of Linear Polarization (DOLP) as detectors of man-made materials. Using the Hyperspectral Polarimetric Image Collection Experiment (SPICE) data collection, we analyze approximately one thousand images and correlate the performance of each of the detection metrics to individual meteorological measurements.

Active polarimetric imaging systems are invaluable tools for biomedical or remote sensing applications but they have higher cost and complexity than standard imagers. An important issue is thus to determine under which condition they yield better performance, and what is their optimal number of measurements. Recent advances have made it possible to give quantitative answers to these questions, and we will illustrate these results on some examples.

The Spectral and Polarimetric Imagery Collection Experiment (SPICE) is an ongoing collaborative effort that commenced in February 2010 between the US Army ARDEC and Army Research Laboratory (ARL). SPICE is focused on the collection of mid-wave and long-wave infrared imagery using hyperspectral, polarimetric, and broadband sensors. The overall objective of SPICE is to collect a comprehensive database of the different modalities spanning multiple years to capture sensor performance encompassing a wide variety of meteorological (MET) conditions, diurnal, and seasonal changes inherent to Picatinny's northern New Jersey location. Utilizing the Precision Armament Laboratory (PAL) tower at Picatinny Arsenal, the sensors are autonomously collecting the desired data around the clock at multiple ranges containing surrogate 2S3 Self-Propelled Howitzer targets positioned at different orientations in an open woodland field. This database allows for: 1) Understanding of signature variability under adverse weather conditions; 2) Development of robust algorithms; 3) Development of new sensors; 4) Evaluation of polarimetric technology; and 5) Evaluation of fusing the different sensor modalities. In this paper, we will revisit the SPICE data collection objectives and the sensors deployed. We will present, in a statistical sense, the integrity of the data in the long-wave infrared (LWIR) polarimetric database collected from February through September 2010 and issues and lessons learned associated with a fully autonomous, around the clock data collection. We will also demonstrate sample LWIR polarimetric imagery and the performance of the Stokes parameters under adverse weather conditions.

We present a real-time polarization measurement method with a space-variant phase retarder in liquid crystal polymers. This retarder presents a continuous and periodical variation of its optical axis orientation. The method computes the Stokes parameters of an incident beam by studying the intensity distribution after the retarder and a linear polarizer. This paper contains the mathematical modelization, the numerical simulation, the description of the experimental setup, the results for several completely polarized beams and the future developments of this method.

In this work, we present the design, optimization and implementation of dynamic Stokes polarimeters based on a single Twisted Nematic Liquid Crystal (TN-LC) panel. TN-LC material enables both to introduce a retardance and to rotate the polarization ellipse orientation. For this reason, a simple setup composed by a transmissive TN-LC panel and a polarizer can be built, leading to a complete Stokes polarimeter. Variations of the initial setup are analyzed with the aim of minimizing the noise propagation to the Stokes vector calculations. In particular, working out of normal incidence to the TN-LC panel and working on TN-LC reflective mode. Moreover, we carry out an optimization of the polarization analyzers used in each configuration. Finally, we implement the optimized polarimeters and some incident Stokes vectors are measured, proving their correct operation. Results are compared with those provided by a commercial polarimeter and so, the suitability of applying a TN-LC panel on polarimeters design is confirmed.

The channeled spectropolarimeter using a wavelength-scanning laser and a channeled spectroscopic polarization state generator is discussed. This implementation has a feature that it is applicable for the spatial mapping of the polarimetric parameters. Since no spectrometer is used and both the wavelength scanning and the polarization modulation are made within the illumination optics, a standard imaging optics followed by a CCD camera can be easily incorporated for the two-dimensional measurement. Another feature of this implementation is its capability for the high wavelength-resolution acquisition of the channeled spectrum. This feature is useful for the full Mueller matrix measurement.

We present results from a SWIR/MWIR infrared hyperspectral imaging polarimeter (IHIP). The sensor includes a pair of sapphire Wollaston prisms and several high order retarders to form an imaging Fourier transform spectropolarimeter. The Wollaston prisms serve as a birefringent interferometer with reduced sensitivity to vibration versus an unequal path interferometer, such as a Michelson. Polarimetric data are acquired through the use of channeled spectropolarimetry to modulate the spectrum with the Stokes parameter information. We discuss the operation of the IHIP sensor, in addition to our calibration techniques. Lastly, spectropolarimetric results from the laboratory and outdoor tests are presented.

A snapshot channeled linear imaging (CLI) polarimeter is demonstrated by incorporating two identical polarization gratings (PGs) into a shearing polarization interferometer. Placing the PGs in series causes the shear to become linearly proportional to the wavelength, thereby generating white-light polarization fringes at the focal point of an imaging lens. These fringes amplitude modulate the incident Stokes parameters corresponding to linearly polarized light (S0, S1, and S2). In this paper, we theoretically and experimentally demonstrate the CLI polarimeter. Additional validation of the technique is conducted through outdoor measurements of moving targets, and extending the measurement capacity of the system to include circularly polarized light is theoretically demonstrated.

A pixel-level micropolarizer array bonded to a scientific camera has been developed for use in commercial dynamic interferometers. The pixelated array includes the 0, 45, 90, and, 135 degree polarization orientations. Micropolarizer arrays with elements as small as 7.4 microns and array sizes as large 4 Mega-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 interferometric or polarimetric measurements. Examples of each type of measurement are presented. Details of how the pixelated camera is used in interferometry are reviewed and the spatial resolution performance of the camera when used in interferometry is discussed.

Objective and background: We present a new version of Bossa Nova Technologies' passive polarization imaging camera. The previous version was performing live measurement of the Linear Stokes parameters (S₀, S₁, S₂), and its derivatives. This new version presented in this paper performs live measurement of Full Stokes parameters, i.e. including the fourth parameter S₃ related to the amount of circular polarization. Dedicated software was developed to provide live images of any Stokes related parameters such as the Degree Of Linear Polarization (DOLP), the Degree Of Circular Polarization (DOCP), the Angle Of Polarization (AOP). Results: We first we give a brief description of the camera and its technology. It is a Division Of Time Polarimeter using a custom ferroelectric liquid crystal cell. A description of the method used to calculate Data Reduction Matrix (DRM)^5,9 linking intensity measurements and the Stokes parameters is given. The calibration was developed in order to maximize the condition number of the DRM. It also allows very efficient post processing of the images acquired. Complete evaluation of the precision of standard polarization parameters is described. We further present the standard features of the dedicated software that was developed to operate the camera. It provides live images of the Stokes vector components and the usual associated parameters. Finally some tests already conducted are presented. It includes indoor laboratory and outdoor measurements. This new camera will be a useful tool for many applications such as biomedical, remote sensing, metrology, material studies, and others.

The use of Liquid Crystal Variable Retarders (LCVRs) as polarization modulators are envisaged as a promising novel technique for space instrumentation due to the inherent advantage of eliminating the need for conventional rotary polarizing optics hence the need of mechanisms. LCVRs is a mature technology for ground applications; they are wellknow, already used in polarimeters, and during the last ten years have undergone an important development, driven by the fast expansion of commercial Liquid Crystal Displays. In this work a brief review of the state of the art of imaging polarimeters based on LCVRs is presented. All of them are ground instruments, except the solar magnetograph IMaX which flew in 2009 onboard of a stratospheric balloon as part of the SUNRISE mission payload, since we have no knowledge about other spaceborne polarimeters using liquid crystal up to now. Also the main results of the activity, which was recently completed, with the objective to validate the LCVRs technology for the Solar Orbiter space mission are described. In the aforementioned mission, LCVRs will be utilized in the polarisation modulation package of the instruments SO/PHI (Polarimetric and Helioseismic Imager for Solar Orbiter) and METIS/COR (Multi Element Telescope for Imaging and Spectroscopy, Coronagraph).

We present the Spectropolarimeter for Planetary EXploration (SPEX), a high-accuracy linear spectropolarimeter measuring from 400 to 800 nm (with 2 nm intensity resolution), that is compact (~ 1 liter), robust and lightweight. This is achieved by employing the unconventional spectral polarization modulation technique, optimized for linear polarimetry. The polarization modulator consists of an achromatic quarter-wave retarder and a multiple-order retarder, followed by a polarizing beamsplitter, such that the incoming polarization state is encoded as a sinusoidal modulation in the intensity spectrum, where the amplitude scales with the degree of linear polarization, and the phase is determined by the angle of linear polarization. An optimized combination of birefringent crystals creates an athermal multiple-order retarder, with a uniform retardance across the field of view. Based on these specifications, SPEX is an ideal, passive remote sensing instrument for characterizing planetary atmospheres from an orbiting, air-borne or ground-based platform. By measuring the intensity and polarization spectra of sunlight that is scattered in the planetary atmosphere as a function of the single scattering angle, aerosol microphysical properties (size, shape, composition), vertical distribution and optical thickness can be derived. Such information is essential to fully understand the climate of a planet. A functional SPEX prototype has been developed and calibrated, showing excellent agreement with end-to-end performance simulations. Calibration tests show that the precision of the polarization measurements is at least 2 • 10^-4. We performed multi-angle spectropolarimetric measurements of the Earth's atmosphere from the ground in conjunction with one of AERONET's sun photometers. Several applications exist for SPEX throughout the solar system, a.o. in orbit around Mars, Jupiter and the Earth, and SPEX can also be part of a ground-based aerosol monitoring network.

This paper will describe the Marshall Space Flight Center's Solar Ultraviolet Magnetograph (SUMI) sounding rocket program, with emphasis on the polarization characteristics of the VUV optics and their spectral, spatial and polarization resolution. SUMI's first flight (7/30/2010) met all of its mission success criteria and this paper will describe the data that was acquired with emphasis on the MgII linear polarization measurements.

A dual rotating retarder Mueller matrix polarimeter is described that operates in the UV-VIS-NIR region. The components were selected to allow the instrument to seamlessly span the 300-1100 nm region with a resolution of 2 nm or higher. Complete Mueller matrix polarimetric characterizations of a host of optical components have been performed and a select few will be presented. This instrumentation is expected to enable exploratory research into novel methods for point and standoff detection of chemical and biological threats in the atmosphere. To this end, surrogates of hazardous materials as well as background aerosols must be characterized and differentiating features in the polarization properties correlated to specific morphologies. Investigations specific to this application is underway.

The goal of this study is to develop a spectropolarimeter for purposes of assessing polarization signatures in skin scattering on a regional scale. Prior research has that certain skin lesions have identifiable polarization signatures;1-3 however, those studies were limited to single lesion evaluation and are not convenient for screening patients with many suspicious legions. As a precursor to the future instrument, a simple actively illuminated Stokes spectropolarimeter was constructed to gather preliminary data about expected signatures and the required performance (resolution, wavelength, polarization state, etc.). This spectropolarimeter consists of a rotating retarder and a hyperspectral camera4 that scans through wavelengths by means of a Liquid Crystal Tunable Filter (LCTF). Data is captured in a serial fashion, where LCTF scans through eight wavelengths at each of the four retarder orientations. With a single acquisition taking 23 seconds to complete, it makes the issue of image registration very important. After proper alignment, the acquired images reveal that wavelength-dependent polarization signatures exist on a regional scale. In particular, it was found that polarization factors such as Degree of Linear Polarization (DoLP) tend to suppress many uninteresting skin features like wrinkles and skin texture, while capturing information that is not necessarily apparent in the intensity image.

To estimate aerosol properties, the PSR-1000 polarimeter measures the radiance of direct sunlight and the radiance and polarization of atmospheric light. PSR-1000 has been calibrated once a year by the Langley plot method at Mt. Haleakala Observatory in Maui Island, Hawaii, and so on. To improve the derivation of aerosol optical thickness, precise correction of molecular scattering and gaseous absorption is desired. Therefore the gaseous absorption by water vapor, O₂ and NO₂are reexamined at present. It is of interest to mention that PSR-1000 detects atmospheric particles over an urban area recorded among our long-term observations.