Showing papers on "Polarimetry published in 2004"

A review of polarimetry in the context of synthetic aperture radar: concepts and information extraction

Abstract: This study provides an update of the polarimetric tools currently being used for optimum information extraction from polarimetric synthetic aperture radar (SAR) images. The basics of polarimetric theory are summarized and discussed in the context of SAR. Calibration of polarimetric SAR, which is an important issue for the extraction of meaningful polarization information, is reviewed. Information extraction using the scattered and received wave parameters and target decomposition theory is considered. In particular, the use of coherent versus incoherent target decomposition is discussed and the practical limitations of these target decompositions are outlined. Speckle filtering and classification of polarimetric SAR images are also thoroughly analyzed, and the important directions for future research are outlined.

Using polarimetry to detect and characterize Jupiter-like extrasolar planets

Abstract: Using numerical simulations of flux and polarization spectra of visible to near-infrared starlight reflected by Jupiter-like extrasolar planets, we show that polarimetry can be used both for the detection and for the characterization of extrasolar planets. Polarimetry is valuable for detection because direct, unscattered starlight is generally unpolarized, while starlight that has been reflected by a planet will generally be polarized. Polarimetry is valuable for planet characterization because the degree of polarization of starlight that has been reflected by a planet depends strongly on the composition and structure of the planetary atmosphere.

Polarimetric imaging of crystals

Abstract: Classical crystal optics has recently undergone a renaissance as developments in optical microscopy and polarimetry, enabled in part by sensitive imaging CCD cameras and personal computers, now permit the analytical separation of various optical effects that are otherwise convolved in polarized light micrographs. In this tutorial review, we review recent developments in the measurement of the principal crystallo-optical quantities including linear birefringence, linear dichroism, circular birefringence, and circular dichroism, as well as new effects in crystal optics encountered in unusual mixed crystals. The new microscopies and polarimetries are applied to problems of crystallographic twinning, phase transformations, stress birefringence, symmetry reduction, and the design of new crystalline materials.

Target detection with a liquid-crystal-based passive Stokes polarimeter

Abstract: We present an imaging system that measures the polarimetric state of the light coming from each point of a scene. This system, which determines the four components of the Stokes vector at each spatial location, is based on a liquid-crystal polarization modulator, which makes it possible to acquire four-dimensional Stokes parameter images at a standard video rate. We show that using such polarimetric images instead of simple intensity images can improve target detection and segmentation performance.

Radio Astronomical Polarimetry and Point-Source Calibration

Abstract: A mathematical framework is presented for use in the experimental determination of the polarimetric response of observatory instrumentation. Elementary principles of linear algebra are applied to model the full matrix description of the polarization measurement equation by least-squares estimation of nonlinear, scalar parameters. The formalism is applied to calibrate the center element of the Parkes Multibeam receiver using observations of the millisecond pulsar PSR J0437-4715 and the radio galaxy 3C 218 (Hydra A).

Photopolarimetry in remote sensing

Abstract: Preface. General Information. Maxwell's Equations, Electromagnetic Waves and Stokes Parameters M.I. Mishchenko, L.D. Travis. Polarized Light Scattering by Large Nonspherical Particles A. Macke, K. Muinonen. Optimization of Numerical Inversion in Photopolarimetric Remote Sensing O. Dubovik. Radiative Transfer. Eigenvalue Shifting - A New Analytical-Computational Method in Radiative Transfer Theory H. Domke. Quadratic Integrals in Inverse Problems with Multiple Scattering T. Viik, N.J. McCormick. Dynamic Systems. Polarization Fluctuation Spectroscopy K.I. Hopcraft, et al. Intensity and Polarization Fluctuation Statistics of Light Scattered by Systems of Particles F. Gonzalez, et al. Backscatter Polarization. Scattering Properties of Planetary Regoliths near Opposition Y. Shkuratov, et al. Backscattering from Particles near Planar Surfaces G. Videen, K. Muinonen. Backscattering Effects for Discrete Random Media V. Tishkovets, et al. Biological Systems. Inverse Polarimetry and Light Scattering by Leaves S.N. Savenkov, R.S. Muttiah. Optical Properties and Biomedical Applications of Nanostructures Based on Gold and Silver Bioconjugates N.G. Khlebtsov, et al. Astrophysical Phenomena. Polarization of Light by Young Stellar Objects V.P. Grinin. Infrared Polarimatry of Interstellar Dust J.H. Hough, D.K. Aitken. Measurements of General Magnetic Fields on Stars with Vigorous Convective Zones Using High-Accuracy Spectropolarimetry S.I. Plachinda. Polarimetry and Physics of Solar System Bodies A. Morozhenko, A. Vid'machenko. Disk-Integrated Polarimetry of Mercury in 2000-2002 D. Lupishko, N. Kiselev.Comets. Polarimetry of Dust in the Solar System: Observations and Measurements A. Chantal Levasseur-Regourd. Polarimetry of Comets: Progress and problems N. Kiselev, V. Rosenbush. Characterization of Dust Particles Using Photopolarimetric Data: Example of Cometary Dust L. Kolokolova, et al. Photopolarimetry Instrumentation. Invitation to Spectropolarimetry Y. Yefimov. Astronomical Polarimeters and Features of Polarimetric Observations A. Morozhenko, A. Vid'machenko. Attendees. Index.

Solar polarimetry in the near UV with the Zurich Imaging Polarimeter ZIMPOL II

Abstract: We describe an imaging polarimeter for high sensitivity measurements of solar polarisation signals in the wavelength range from 300 nm to 1 μ m. At higher wavelengths the system is limited by the wavelength cut-off of the silicon CCD sensor used. To the blue the limitation arises from the atmospheric cut-off around 310 nm. The complete system is a modified version of the Z urich Im aging Pol arimeter ZIMPOL ii which has been equipped with a special CCD sensor. The CCD combines for the first time a so-called open electrode structure with on-chip demodulation. The concept as well as the detailed design of the instrument are presented. Examples of observations are shown and interpreted in order to experimentally evaluate the performance of the system.

Polarimetry toward the Musca Dark Cloud. I. The Catalog

Abstract: We have used CCD imaging polarimetry to obtain linear polarization measurements of background stars toward the filamentary Musca dark cloud. We present a catalog of 2497 objects with polarization signal-to-noise ratio larger than 5. This allows us to build polarization maps to infer the detailed geometry of the local magnetic field. We show composite polarization maps along the cloud and explore general correlations of the polarimetric data with the morphology of the region. We find the overall field to be strikingly aligned with the projected small axis of the filamentary cloud. We detect a lower limit for the polarization across the cloud of ~2%, with an enhanced polarization of 6%-7% in the central region. We find evidence that the polarization pattern is altered in the inner regions, those associated with higher extinction.

Remote sensing using passive infrared Stokes parameters

Abstract: We address the problem of detecting vehicle targets on the ground by means of an autonomous polarimetric sensor on board a high-altitude air- or spaceborne platform. We studied a sensor system that incorporates a micropolarizer array, a microscanner, and digital signal processors that host algorithms for detecting small targets. These algorithms use statistical techniques to fuse a target's Stokes-vector infrared signature measurements. Fusion is achieved by constructing the joint statistical measures for the target's polarization states. Those states are expressed in terms of the intensity, the percentage of linear polarization, and the angle of the polarization plane. The performance of the sensor system on synthetic polarimetric infrared imagery was evaluated. Relatively good detection and low false-alarm probabilities were achieved even when the number of pixels on targets is as small as four. This is the first report of the development and evaluation of automatic detection in polarimetric imagery containing targets subtending only a small number of pixels.

Realization of quantitative-grade fieldable snapshot imaging spectropolarimeter

Abstract: We discuss achievement of a long-standing technology goal: the first practical realization of a quantitative-grade, field-worthy snapshot imaging spectropolarimeter. The instrument employs Polarimetric Spectral Intensity Modulation (PSIM), a technique that enables full Stokes instantaneous "snapshot" spectropolarimetry with perfect channel registration. This is achieved with conventional single beam optics and a single focal plane array (FPA). Simultaneity and perfect registration are obtained by encoding the polarimetry onto the spectrum via a novel optical arrangement which enables sensing from moving platforms against dynamic scenes. PSIM is feasible across the electro-optical sensing range (UV-LWIR). We present measurement results from a prototype sensor that operates in the visible and near infrared regime (450-900 nm). We discuss in some detail the calibration and Stokes spectrum inversion algorithms that are presently achieving 0.5% polarimetric accuracy.

Improved Precipitation Rates and Data Quality by Using Polarimetric Measurements

Abstract: The additional information provided by polarisation-diversity radar has the potential to remove many of the ambiguities and uncertainties present when only the conventional reflectivity (Z) and Doppler information are available. In this chapter we emphasise the application in an operational environment with a typical one-degree beam-width radar and a dwell time of about one-sixth of a second, so that it completes a PPI every minute and provides rainfall estimates with a spatial resolution of 2 km or better. An excellent and very comprehensive book on polarimetric Doppler weather radar has recently appeared by Bringi and Chandrasekar (2001), and we refer the reader to this book for detailed derivations and analysis which we will simply quote. Essentially, polarimetric radar provides information on the shape and orientation of the radar targets. In Sect. 5.2, we define the polarisation parameters, summarise their applications and discuss the theoretical and practical limits to the accuracy with which they can be estimated. The variation of raindrop shape with size and the typical raindrop size spectra are reviewed in Sect. 5.3. The following sections consider how to exploit the shape and orientation information from a polarimetric radar which can transmit and receive horizontally and vertically polarised radiation, as described by Gekat et al. (2003), this book.

Three-dimensional polarimetric integral imaging.

Abstract: A three-dimensional (3D) polarimetric image sensing and display technique based on integral imaging is proposed. Three-dimensional polarization distribution of reflected light from a 3D object can be measured as elemental image arrays by a rotating linear polarizer. After the measurement of the polarization of the 3D object, the 3D polarimetric object can be reconstructed optically by displaying the polarization-selected elemental images in spatial light modulators with two quarter-wave plates. Experimental demonstration of 3D polarimetric imaging of a 3D object attached to two orthogonal linear polarizers is presented. To the best of our knowledge, this is the first report on 3D polarimetric sensing imaging and 3D optical reconstruction by integral imaging.

Fast wavelength-parallel polarimeter for broadband optical networks.

Abstract: We describe a novel wavelength-parallel polarimeter operating in the light-wave band that measures the complete state of polarization of 256 wavelengths in parallel within 20 ms (software-limited), with the potential for submillisecond operation. By use of fast switching ferroelectric liquid crystals in conjunction with an InGaAs arrayed detector, selection and wavelength-parallel detection of individual polarization components can be achieved within approximately 150 µs. This instrument offers unprecedented sensing capability that is relevant to the compensation of polarization-related impairments in high-speed light-wave communications.

Interferometric imaging polarimeter.

Abstract: We describe a new imaging polarimeter that is based on a modified Sagnac interferometer and allows full polarimetric description of complex random electromagnetic beams from only two images as compared with the four images needed in conventional polarimetry. The procedure is analyzed in terms of the interference laws of Fresnel and Arago, and very good agreement with standard Stokes polarimetry is demonstrated. In certain cases the new technique provides the degree of polarization and the retardance from only one image.

Time-resolved Mueller matrix imaging polarimetry.

Abstract: We present a new method of time-resolved Mueller matrix imaging polarimetry for spatial and temporal characterization of the polarization effects in backscattering from turbid media. The technique allows measuring the time evolution of spatially varying polarization patterns of diffusely backscattered light with picosecond resolution. A series of time-resolved polarization patterns are obtained at various time delays, are analyzed in sequence, and used to separate the polarimetric contributions of different scattering paths. Specific features of the 2D Mueller matrix components corresponding to light backscattered from colloidal suspensions were determined and characterized. The temporally-and spatially-resolved measurements permit detailed analysis of the changes in the magnitude, sign, and the general symmetry properties of Mueller matrix components.

Ferroelectric Liquid Crystal Polarimeter for High-cadence Hα Imaging Polarimetry

Abstract: We developed a polarimeter with ferroelectric liquid crystals (FLCs) to observe polarization of flare kernels in the Hα line. Polarization is one of the important diagnostics of the high-energy particles in solar flares, and high-cadence imaging polarimetry with the precision of the order of 0.1% is required to observe the polarization of flare kernels. However, to achieve such high precision is difficult mainly due to the seeing-induced polarization error, which particularly appears around the flare kernels, because the brightness gradient is steep there. To reduce the seeing-induced error, a high modulation frequency is required, and our new polarimeter based on the combination of a high-speed CCD camera and FLCs realized high-frequency polarization modulation nearly 250 Hz. We evaluated the polarization error, and confirmed that the error was significantly reduced with the new polarimeter. We concluded that the polarimeter with FLCs meets the requirement of solar flare polarimetry.

Near-Infrared Polarimetry and Photometry of Recent Comets

Abstract: We present near-infrared (2.2 μm) imaging polarimetry and near-infrared photometry for recent comets. The 2.2 μm polarization as a function of phase angle is 1%–2% higher than typical comet visual narrowband red polarization. This implies a general, but weak, trend to higher polarization at wavelengths longer than 0.7 μm. As found with visual narrowband red polarimetry, comets appear to divide into a high- and a low-polarization class at 2.2 μm as well. The high-polarization class is characterized by moderate to strong mid-infrared silicate emission, while the low-polarization class is characterized by weak to absent silicate emission. In contrast to C/1995 O1 (Hale-Bopp) and some other dusty comets, no significant grain population radial gradient is seen in any of the polarization maps for the six comets in our sample with near-infrared imaging polarimetry. Our analysis of previously published Hale-Bopp data shows that the polarization at 40° phase angle varies by only about a factor of 1.6 from 0.3 to 2.2 μm and is nearly flat from 0.7 to 2.2 μm. Any model of comet dust must reproduce this weak wavelength dependence.

Ocean wave spectra from a linear polarimetric SAR

Abstract: Conventional horizontal or vertical polarization synthetic aperture radar (SAR) images seldom perform well in detecting azimuthally traveling ocean waves. However, theoretical analyses suggest that linear-polarimetric backscatter measurements may be more sensitive to these waves and, therefore, that a SAR with linear polarization is expected to give a better measurement of azimuthally traveling ocean waves. We derive the polarization-orientation modulation transform function and tilt modulation transform function of the linear-polarimetric SAR. Through numerical simulations based on these formulations, we examine the effects of radar and ocean wave parameters on linear-polarimetric SAR image spectra. We suggest a method to eliminate the 180/spl deg/ directional ambiguity in determining the true wave direction. Our numerical simulations show that the correlation between ocean wave spectra and SAR image spectra is improved for larger radar incidence angles and longer ocean waves. For real aperture radar, we suggest that the polarimetric modulation allows measurement of waves traveling in the azimuth direction. Moreover, as suggested by Schuler et al., this may be the dominant modulation for many SAR aircraft measurements, particularly for moderate sea states.

Contrast definition for optical coherent polarimetric images

Abstract: We consider polarimetric images formed with coherent waves, such as in laser-illuminated imagery or synthetic aperture radar A definition of the contrast between regions with different polarimetric properties in such images is proposed, and it is shown that the performances of maximum likelihood-based detection and segmentation algorithms are bijective functions of this contrast parameter This makes it possible to characterize the performance of such algorithms by simply specifying the value of the contrast parameter

Polarimetric scene simulation in millimeter-wave radiometric imaging

Abstract: This paper describes the general requirements and an approach to scene simulation in millimetre wave radiometric imaging that is based on multi faceted semitransparent layered media in the earth’s three-dimensional geometry. The driving attributes in this field are essentially the transparency of clothing for security scanning and the transparency of fog, cloud, rain and dust for all weather flight. Out-door illumination and the physics of the interaction of millimetre waves with the atmosphere and obscurants are discussed, together with the interaction of millimetre waves with multi layer material surfaces, giving rise to transmission, reflection and emission. The physics of these interactions are discussed in the context of computer graphics. These considerations enable a powerful polarimetric modelling capability to be developed that can be used to simulate all scenarios, including artificial or burst illumination, from in-doors to imaging from satellites.

The Diffraction Limited Spectro-Polarimeter: a new instrument for high-resolution solar polarimetry

Abstract: The National Solar Observatory in collaboration with the High-Altitude Observatory is developing a new solar polarimeter, the Diffraction Limited Spectro-Polarimeter. In conjunction with a new high-order adaptive optics system at the NSO Dunn Solar Telescope, the DLSP design facilitates very high angular resolution observations of solar vector magnetic fields. This project is being carried out in two phases. As a follow-on to the successful completion of the first phase, the ongoing DLSP Phase II implements a high QE CCD camera system, a ferro-electric liquid crystal modulator, and a new opto-mechanical system for polarization calibration. This paper documents in detail the development of the modulator system and its performance, and presents preliminary results from an engineering run carried out in combination with the new NSO high-order AO system.

Characterization of bidimensional gratings by spectroscopic ellipsometry and angle-resolved Mueller polarimetry.

Abstract: We studied two bidimensional square gratings of square holes formed in photoresist layers deposited on silicon wafers, both by classical spectroscopic ellipsometry (1.5–4.5-eV spectral range) at a constant incidence angle (70.7°) and by angle-resolved Mueller polarimetry at a constant wavelength (532 nm). The grating period was 1 μm in both directions, and the nominal hole sizes were 250 and 500 nm, respectively. The ellipsometric spectra were fitted by rigorous coupled-wave analysis simulations with two adjustable parameters, the resist layer thickness and the hole size. These parameters were found to be in good agreement with independent scanning electron microscopy measurements. The experimental angle-resolved Mueller spectra were remarkably well reproduced by the simulations, showing that angle-resolved Mueller polarimetry has a great potential for grating metrology applications.

Advanced polarization imaging method, apparatus, and computer program product for retinal imaging, liquid crystal testing, active remote sensing, and other applications

Abstract: A method, apparatus, and computer program product for identifying features in a sample by analyzing Mueller matrices to calculate an average degree of polarization, a weighted average degree of polarization, a degree of polarization map, a degree of polarization surface. Also, a method, apparatus, and computer program product for identifying features in a sample by analyzing Mueller matrices to calculate depolarization relative to a retardance axis and/or a diattentuation axis, and to calculate a ratio of diattenuation to polarizance or ratios of row and column magnitudes. Also, a method for retinal polarimetry, including a non-depolarizing light tube configured for insertion into the eye.

Emissivity Measurements on Metallic Surfaces with Various Degrees of Roughness: A Comparison of Laser Polarimetry and Integrating Sphere Reflectometry

Abstract: Both integrating sphere reflectometry (ISR) as well as laser polarimetry have their advantages and limitations in their ability to determine the normal spectral emissivity of metallic samples. Laser polarimetry has been used for years to obtain normal spectral emissivity measurements on pulse-heated materials. The method is based on the Fresnel equations, which describe reflection and refraction at an ideally smooth interface between two isotropic media. However, polarimetry is frequently used with surfaces that clearly deviate from this ideal condition. Questions arise with respect to the applicability of the simple Fresnel equations to non-specular surfaces. On the other hand, reflectometry utilizing integrating spheres provides a measurement of the hemispherical spectral reflectance, from which the normal spectral emissivity can be derived. ISR provides data on spectral-normal-hemispherical reflectance and, hence, normal spectral emissivity for a variety of surfaces. However, the resulting errors are minimal when both the sample and the reference have a similar bidirectional reflectance distribution function (BRDF). In an effort to explore the limits of polarimetry in terms of surface roughness, room temperature measurements on the same samples with various degrees of roughness were performed using both ISR and a laser polarimeter. In this paper the two methods are briefly described and the results of the comparison are discussed.

Estimation of the degree of polarization in active coherent imagery by using the natural representation.

Abstract: We address the problem of degree of polarization estimation in polarization diversity images. We consider active imaging techniques with laser illumination, which have the appealing feature of revealing contrasts that do not appear in conventional intensity images. These techniques provide two images of the same scene that are perturbed with speckle noise. Because of the presence of nonhomogeneity in the reflected intensity, it can be preferable to perform image analysis of the orthogonal-state contrast image, which is a measure of the degree of polarization of the reflected light when the coherency matrix is diagonal. It has been shown that a simple nonlinear transformation of this orthogonal-state contrast image leads to an image perturbed with additive symmetrical noise on which simple and efficient estimation and detection techniques can be applied. We propose to precisely analyze estimation properties of the degree of polarization using this natural representation. In particular, we determine the Cramer–Rao bound of the polarization degree estimation and the variance of the proposed estimator, and we study the estimator’s efficiency as a function of the speckle order for different measurement strategies.

Mid-infrared polarimetry and magnetic fields : an observing strategy

Abstract: Linear polarimetry in the mid-infrared can be used to obtain magnetic field directions in astronomical sources. However, since the polarization can arise from emission and/or absorption from aligned grains, care is needed to plan observations so that enough information is obtained to identify and separate the components of polarization. Procedures for doing this from spectropolarimetry, and from polarimetric imaging at a minimum of two wavebands and making an appropriate filter choice, are presented here, together with an example.

Mars orbital synthetic aperture radar: Obtaining geologic information from radar polarimetry

Abstract: [1] Radar penetration of mantling layers, and scattering from buried objects or interfaces, is a topic of current interest in both terrestrial and planetary remote sensing. We examine the behavior of surface and subsurface scattering interfaces and the types of information that may be obtained from observations in different polarizations and wavelengths. These results are applied to the design of a future Mars orbital synthetic aperture radar (SAR), for which we draw the following conclusions. (1) Mapping of buried geologic features is best accomplished using VV polarization, at an optimal wavelength determined by the competing effects of antenna gain, attenuation in the dust, and the reduction in effective surface roughness with wavelength. P band frequencies (∼1 GHz or less) offer the best opportunity for detection of moderately rough, buried features. (2) The relative roles of surface and subsurface scattering may be determined using measurements in HH and VV polarization, with a channel gain calibration better than 0.5 dB. (3) The thickness of a mantling layer (or ice mass) cannot be directly inferred from multiwavelength observations. Layer thickness may be inferred from the interferometric correlation of backscatter measurements collected on suitably spaced orbital passes, though the required phase measurement accuracy is challenging. While additional information may be gained by collecting scattering data in more polarizations or wavelengths, we suggest that the primary science goals of a Mars-orbiting radar could be accomplished by a single-wavelength system capable of collecting VV and HH polarizations with the calibration and orbit control needed to permit interferometric analysis.