Showing papers on "Polarimetry published in 2012"
TL;DR: In this paper, a silicon photodetector integrated with a set of plasmonic structures was used as either a broadband linear-Stokes polarimeter or a narrowband full-stokes polarimeters capable of determining the complete state of polarization of a light beam.
Abstract: Abstract Plasmonics has started to facilitate the replacement of bulky optical components in optical systems by compact nanometallic elements that perform the same function. This allows for a natural and very dense integration with electronic devices. In this vein, we present a silicon (Si) photodetector integrated with a set of plasmonic structures that can be used as either a broadband linear-Stokes polarimeter or a narrowband full-Stokes polarimeter capable of determining the complete state of polarization of a light beam. At a probe-wavelength of 830 nm, our experimental results show contrast ratios of 25 and 1.13 for orthogonal linear and circular states of polarization, in good agreement with simulations. The resulting device is lightweight, orders of magnitude smaller than conventional polarimeters, and mechanically robust. For these reasons, there promises to be a wide range of applications including polarimetric imaging and sensing.
127 citations
TL;DR: In this article, high precision measurements of polarization rotations in the frequency range from 0.1 to 2.5 THz using a polarization modulation technique are presented. But the precision of these measurements depends on the angle of the rotation of the polarizer.
Abstract: We present high precision measurements of polarization rotations in the frequency range from 0.1 to 2.5 THz using a polarization modulation technique. A motorized stage rotates a polarizer at ∼ 80 Hz, and the resulting modulation of the polarization is measured by a lock-in technique. We achieve an accuracy of 0.050° (900 μrad) and a precision of 0.02° (350 μrad) for small rotation angles. A detailed mathematical description of the technique is presented, showing its ability to fully characterize elliptical polarizations from 0.1 to 2.5 THz.
96 citations
TL;DR: A snapshot imaging Mueller matrix polarimeter (SIMMP) is theoretically described and empirically demonstrated through simulation to demonstrate the system's performance in the presence of noise.
Abstract: A snapshot imaging Mueller matrix polarimeter (SIMMP) is theoretically described and empirically demonstrated through simulation. Spatial polarization fringes are localized onto a sample by incorporating polarization gratings (PGs) into a polarization generator module. These fringes modulate the Mueller matrix (MM) components of the sample, which are subsequently isolated with PGs in an analyzer module. The MM components are amplitude modulated onto spatial carrier frequencies which, due to the PGs, maintain high visibility in spectrally broadband illumination. An interference model of the SIMMP is provided, followed by methods of reconstruction and calibration. Lastly, a numerical simulation is used to demonstrate the system’s performance in the presence of noise.
86 citations
TL;DR: High precision measurements of polarization rotations in the frequency range from 0.1 to 2.5 THz using a polarization modulation technique are presented, showing its ability to fully characterize elliptical polarizations.
Abstract: We present high precision measurements of polarization rotations in the frequency range from 0.1 to 2.5 THz using a polarization modulation technique. A motorized stage rotates a polarizer at ~80 Hz, and the resulting modulation of the polarization is measured by a lock-in technique. We achieve an accuracy of 0.05° (900 {\mu}rad) and a precision of 0.02° (350 {\mu}rad) for small rotation angles. A detailed mathematical description of the technique is presented, showing its ability to fully characterize elliptical polarizations from 0.1 to 2.5 THz.
84 citations
TL;DR: Fast Holographic Deconvolution as mentioned in this paper is an extension of A-projection/software-holography/forward modeling analysis techniques and shares their precision deconvolution and widefield polarimetry.
Abstract: We introduce the Fast Holographic Deconvolution method for analyzing interferometric radio data. Our new method is an extension of A-projection/software-holography/forward modeling analysis techniques and shares their precision deconvolution and widefield polarimetry, while being significantly faster than current implementations that use full direction-dependent antenna gains. Using data from the MWA 32 antenna prototype, we demonstrate the effectiveness and precision of our new algorithm. Fast Holographic Deconvolution may be particularly important for upcoming 21 cm cosmology observations of the Epoch of Reionization and Dark Energy where foreground subtraction is intimately related to the precision of the data reduction.
80 citations
TL;DR: An optical system that performs Stokes polarimetric imaging with a single-pixel detector is presented, possible by applying the theory of compressive sampling to the data acquired by a commercial polarimeter without spatial resolution.
Abstract: We present an optical system that performs Stokes polarimetric imaging with a single-pixel detector. This fact is possible by applying the theory of compressive sampling to the data acquired by a commercial polarimeter without spatial resolution. The measurement process is governed by a spatial light modulator, which sequentially generates a set of preprogrammed light intensity patterns. Experimental results are presented and discussed for an object that provides an inhomogeneous polarization distribution.
70 citations
University of Leicester1, Paris Diderot University2, University of Copenhagen3, Liverpool John Moores University4, INAF5, University of Amsterdam6, Spanish National Research Council7, Max Planck Society8, University of Ljubljana9, University of Ferrara10, Marshall Space Flight Center11, University of Warwick12
TL;DR: In this paper, the authors presented the first high-quality multi-night polarimetric light curve of a Swift gamma-ray burst (GRB) afterglow, aimed at providing a well-calibrated data set of a typical GRB to serve as a benchmark system for modelling afterglove polarization behavior.
Abstract: Follow-up observations of large numbers of gamma-ray burst (GRB) afterglows, facilitated by the Swift satellite, have produced a large sample of spectral energy distributions and light curves, from which their basic micro- and macro-physical parameters can in principle be derived. However, a number of phenomena have been observed that defy explanation by simple versions of the standard fireball model, leading to a variety of new models. Polarimetry can be a major independent diagnostic of afterglow physics, probing the magnetic field properties and internal structure of the GRB jets. In this paper we present the first high-quality multi-night polarimetric light curve of a Swift GRB afterglow, aimed at providing a well-calibrated data set of a typical afterglow to serve as a benchmark system for modelling afterglow polarization behaviour. In particular, our data set of the afterglow of GRB 091018 (at redshift z = 0.971) comprises optical linear polarimetry (R band, 0.13–2.3 d after burst); circular polarimetry (R band) and near-infrared linear polarimetry (Ks band). We add to that high-quality optical and near-infrared broad-band light curves and spectral energy distributions as well as afterglow spectroscopy. The linear polarization varies between 0 and 3 per cent, with both long and short
65 citations
TL;DR: In this paper, the authors present the first high quality multi-night polarimetric light curve of a Swift GRB afterglow, aimed at providing a well calibrated dataset of a typical GRB to serve as a benchmark system for modelling afterglove polarisation behavior.
Abstract: [Abridged] A number of phenomena have been observed in GRB afterglows that defy explanation by simple versions of the standard fireball model, leading to a variety of new models. Polarimetry can be a major independent diagnostic of afterglow physics, probing the magnetic field properties and internal structure of the GRB jets. In this paper we present the first high quality multi-night polarimetric light curve of a Swift GRB afterglow, aimed at providing a well calibrated dataset of a typical afterglow to serve as a benchmark system for modelling afterglow polarisation behaviour. In particular, our dataset of the afterglow of GRB 091018 (at redshift z=0.971) comprises optical linear polarimetry (R band, 0.13 - 2.3 days after burst); circular polarimetry (R band) and near-infrared linear polarimetry (Ks band). We add to that high quality optical and near-infrared broadband light curves and spectral energy distributions as well as afterglow spectroscopy. The linear polarisation varies between 0 and 3%, with both long and short time scale variability visible. We find an achromatic break in the afterglow light curve, which corresponds to features in the polarimetric curve. We find that the data can be reproduced by jet break models only if an additional polarised component of unknown nature is present in the polarimetric curve. We probe the ordered magnetic field component in the afterglow through our deep circular polarimetry, finding P_circ < 0.15% (2 sigma), the deepest limit yet for a GRB afterglow, suggesting ordered fields are weak, if at all present. Our simultaneous R and Ks band polarimetry shows that dust induced polarisation in the host galaxy is likely negligible.
63 citations
TL;DR: A system of measurements is presented here that shows how a number of factors in the imaged scene can determine the quality of a division-of-focal-plane polarimeter.
Abstract: The development of high resolution division-of-focal-plane polarimeters in the visible spectrum allows real-time capture of two chief properties of interest, the degree of linear polarization and the angle of polarization. The accuracy of these two parameters can be influenced by a number of factors in the imaged scene, from the incident intensity and wavelength to the lens used for image capture. The alignment, transmission, and contrast ratios of the pixel matched filters also impact the measured parameters. A system of measurements is presented here that shows how these factors can determine the quality of a division-of-focal-plane polarimeter.
62 citations
TL;DR: The robustness and simplicity of the approach, coupled with its potential for high sensitivity, and applicability over a wide wavelength range, is likely to prove useful for applications in challenging environments such as space.
Abstract: We present an approach to spectropolarimetry that requires neither moving parts nor time dependent modulation, and that offers the prospect of achieving high sensitivity. The technique applies equally well, in principle, in the optical, UV, or IR. The concept, which is one of those generically known as channeled polarimetry, is to encode the polarization information at each wavelength along the spatial dimension of a two-dimensional data array using static, robust optical components. A single 2D data frame contains the full polarization information and can be configured to measure either two or all of the Stokes polarization parameters. By acquiring full polarimetric information in a single observation, we simplify polarimetry of transient sources and in situations where the instrument and target are in relative motion. The robustness and simplicity of the approach, coupled with its potential for high sensitivity, and applicability over a wide wavelength range, is likely to prove useful for applications in challenging environments such as space.
60 citations
TL;DR: The Short Wavelength Instrument for the Polarization Explorer (SWIPE) as discussed by the authors is composed of three arrays of multi-mode bolometers cooled at 0.3K, with optical components and filters cryogenically cooled below 4K to reduce the background on the detectors.
Abstract: The balloon-borne LSPE mission is optimized to measure the linear polarization of the Cosmic Microwave Background at large angular scales. The Short Wavelength Instrument for the Polarization Explorer (SWIPE) is composed of 3 arrays of multi-mode bolometers cooled at 0.3K , with optical components and filters cryogenically cooled below 4K to reduce the background on the detectors. Polarimetry is achieved by means of large rotating half-wave plates and wire-grid polarizers in front of the arrays. The polarization modulator is the first component of the optical chain, reducing significantly the effect of instrumental polarization. In SWIPE we trade angular resolution for sensitivity. The diameter of the entrance pupil of the refractive telescope is 45 cm, while the field optics is optimized to collect tens of modes for each detector, thus boosting the absorbed power. This approach results in a FWHM resolution of 1.8, 1.5, 1.2 degrees at 95, 145, 245 GHz respectively. The expected performance of the three channels is limited by photon noise, resulting in a final sensitivity around 0.1-0.2 μK per beam, for a 13 days survey covering 25% of the sky.
TL;DR: In this article, the spatial diversity approach was used to reduce the speckle contrast of a single-laser pulse illumination from a solid-state laser source and an array of semiconductor laser diodes.
Abstract: We present simple illumination devices with built-in speckle reduction using the spatial diversity approach. These devices are based on a waveguide homogenization technique with a transmission efficiency of up to 95%. Even for single-laser pulse illumination from a solid-state laser source a reduction of the speckle contrast by a factor of 4.5 was demonstrated. In detail, we present two different illumination devices based on either a solid-state laser source or an array of semiconductor laser diodes. These illumination devices are used for range-gated imaging and active polarimetry with speckle-free and homogeneous illumination.
TL;DR: In this article, the authors describe implementation and demonstration of a polarization technique adapted for lidar to measure all unique elements of the volume backscatter phase matrix, which allows for detection of preferential orientation within a scattering volume, and may improve scattering inversions on oriented ice crystals.
Abstract: We describe implementation and demonstration of a polarization technique adapted for lidar to measure all unique elements of the volume backscatter phase matrix. This capability allows for detection of preferential orientation within a scattering volume, and may improve scattering inversions on oriented ice crystals. The technique is enabled using a Mueller formalism commonly employed in polarimetry, which does not require the lidar instrument be polarization preserving. Instead, the accuracy of the polarization measurements are limited by the accuracy of the instrument characterization. A high spectral resolution lidar at the National Center for Atmospheric Research was modified to demonstrate this polarization technique. Two observations where the instrument is tilted off zenith are presented. In the first case, the lidar detects flattened large raindrops oriented along the same direction due to drag forces from falling. The second case is an ice cloud approximately 5 km above lidar base that contains preferentially oriented ice crystals in a narrow altitude band.
TL;DR: A polarimetric imaging system based on liquid-crystal modulators that allows generation and analysis of any polarization state on the Poincaré sphere is presented, more versatile than standard Mueller imagers based on optimized, but limited, sets of illumination and analysis states.
Abstract: We present the design and the practical implementation of a polarimetric imaging system based on liquid-crystal modulators that allows generation and analysis of any polarization state on the Poincare sphere. This system is more versatile than standard Mueller imagers that are based on optimized, but limited, sets of illumination and analysis states. Examples of benefits brought by these extra degrees of freedom are illustrated on two different applications: contrast enhancement and extraction of partial polarimetric properties of a scene.
TL;DR: Channeled polarimetry as mentioned in this paper uses static, robust optical components to encode the polarization information at each wavelength along the spatial dimension of a 2D data array, which can be configured to measure either two or all of the Stokes polarization parameters.
Abstract: We present an approach to spectropolarimetry which requires neither moving parts nor time dependent modulation, and which offers the prospect of achieving high sensitivity. The technique applies equally well, in principle, in the optical, UV or IR. The concept, which is one of those generically known as channeled polarimetry, is to encode the polarization information at each wavelength along the spatial dimension of a 2D data array using static, robust optical components. A single two-dimensional data frame contains the full polarization information and can be configured to measure either two or all of the Stokes polarization parameters. By acquiring full polarimetric information in a single observation, we simplify polarimetry of transient sources and in situations where the instrument and target are in relative motion. The robustness and simplicity of the approach, coupled to its potential for high sensitivity, and applicability over a wide wavelength range, is likely to prove useful for applications in challenging environments such as space.
TL;DR: Two generalized statistical detectors are proposed which perform joint detection and fusion of a set of multipolarization radar images which are based on Bayes' test and is of interest when target pixel occupancies are known from, e.g., secondary data.
Abstract: We consider the problem of through-the-wall radar imaging (TWRI), in which polarimetric imaging is used for automatic target detection. Two generalized statistical detectors are proposed which perform joint detection and fusion of a set of multipolarization radar images. The first detector is an extension of a previously proposed iterative target detector for multiview TWRI. This extension allows the detector to automatically adapt to statistics that may vary, depending on target locations and electromagnetic-wave polarizations. The second detector is based on Bayes' test and is of interest when target pixel occupancies are known from, e.g., secondary data. Properties of the proposed detectors are delineated and demonstrated by real data measurements using wideband sum-and-delay beamforming, acquired in a semicontrolled lab environment. We examine the performance of the proposed detectors when imaging both metal objects and humans.
Abstract: Well over 700 exoplanets have been detected to date. Only a handful of these have been observed directly. Direct observation is extremely challenging due to the small separation and very large contrast involved. Imaging polarimetry offers a way to decrease the contrast between the unpolarized starlight and the light that has become linearly polarized after scattering by circumstellar material. This material can be the dust and debris found in circumstellar disks, but also the atmosphere or surface of an exoplanet. We present the design, calibration approach, polarimetric performance and sample observation results of the Extreme Polarimeter, an imaging polarimeter for the study of circumstellar environments in scattered light at visible wavelengths. The polarimeter uses the beam-exchange technique, in which the two orthogonal polarization states are imaged simultaneously and a polarization modulator swaps the polarization states of the two beams before the next image is taken. The instrument currently operates without the aid of Adaptive Optics. To reduce the effects of atmospheric seeing on the polarimetry, the images are taken at a frame rate of 35 fps, and large numbers of frames are combined to obtain the polarization images. Four successful observing runs have been performed using this instrument at the 4.2 m William Herschel Telescope on La Palma, targeting young stars with protoplanetary disks as well as evolved stars surrounded by dusty envelopes. In terms of fractional polarization, the instrument sensitivity is better than 10^-4. The contrast achieved between the central star and the circumstellar source is of the order 10^-6. We show that our calibration approach yields absolute polarization errors below 1%.
TL;DR: An analytical technique based on Stokes polarimetry and the Mueller matrix method and considers not only the circular dichroism properties of the sample, but also the depolarization properties, showing that the results show that the proposed method enables all of the effective parameters to be measured over the full range.
Abstract: An analytical technique based on Stokes polarimetry and the Mueller matrix method is proposed for extracting the effective linear birefringence, linear dichroism, circular birefringence, circular dichroism, linear depolarization, and circular depolarization properties of turbid media. In contrast to existing analytical models, the model proposed extracts the effective parameters in a decoupled manner and considers not only the circular dichroism properties of the sample, but also the depolarization properties. The results show that the proposed method enables all of the effective parameters to be measured over the full range. Moreover, it is shown that the extracted value of the depolarization index is unaffected by the order in which the depolarizing Mueller matrix is decomposed during the extraction procedure. Finally, a method is proposed for calibrating the optical rotation angle of a polystyrene microsphere suspension containing dissolved D-glucose (C6H12O6) powder in accordance with the distance between the sample and the detector. The experimental results show that the sensitivity of the resulting D-glucose measurement is equal to approximately 1.73 deg ∕M. © 2012 Society of Photo-Optical Instrumentation Engi-
TL;DR: It is shown that the Doppler spectra and RCS differences are sufficient to distinguish a walking human from stationary and other moving objects.
Abstract: In this paper, the Doppler spectra of the radar backscatter response of human body and a quadruped are presented at W-band frequencies This study is motivated by the desire to utilize millimeter-wave radars to detect pedestrians against other targets in the radar scene The approach is based on dissecting the radar backscatter to isolate the radar returns from different body parts The forward model is based on an iterative physical optics approach The complex motion of different parts of walking bodies and their amplitude and range of motion is directly reflected in their radar cross section (RCS) and Doppler spectrum bandwidth It is shown that the Doppler spectra and RCS differences are sufficient to distinguish a walking human from stationary and other moving objects Radar polarimetry in conjunction with time-frequency analysis is examined as a method for detecting concealed carried objects The overall backscatter is decomposed into components associated with the limbs and torso which are then utilized to enhance target detection
11 Apr 2012
TL;DR: In this article, deep infrared (Ks-band) imaging polarimetry and radio (1.4 and 4.8 GHz) polarimetric measurements of the enigmatic transient Swift J164449.3+573451 were presented.
Abstract: We present deep infrared (Ks-band) imaging polarimetry and radio (1.4- and 4.8-GHz) polarimetry of the enigmatic transient Swift J164449.3+573451. This source appears to be a short-lived jet phenomenon in a galaxy at redshift z= 0.354, activated by a sudden mass accretion on to the central massive black hole, possibly caused by the tidal disruption of a star. We aim to find evidence for this scenario through linear polarimetry, as linear polarization is a sensitive probe of jet physics, source geometry and the various mechanisms giving rise to the observed radiation. We find a formal Ks-band polarization measurement of Plin= 7.4 ± 3.5 per cent (including systematic errors). Our radio observations show continuing brightening of the source, which allows sensitive searches for linear polarization as a function of time. We find no evidence of linear polarization at radio wavelengths of 1.4 and 4.8 GHz at any epoch, with the most sensitive 3σ limits as deep as 2.1 per cent. These upper limits are in agreement with expectations from scenarios in which the radio emission is produced by the interaction of a relativistic jet with a dense circumsource medium. We further demonstrate how polarization properties can be used to derive properties of the jet in Swift J164449.3+573451, exploiting the similarities between this source and the afterglows of gamma-ray bursts.
01 Jan 2012
TL;DR: The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLAST-Pol) as mentioned in this paper is a suborbital mapping experiment designed to study the role played by magnetic fields in the star formation process.
Abstract: The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLAST-Pol) is a suborbital mapping experiment designed to study the role played by magnetic fields in the star formation process. BLAST-Pol is the reconstructed BLAST telescope, with the addition of linear polarization capability. Using a 1.8m Cassegrain telescope, BLAST-Pol images the sky onto a focal plane that consists of 280 bolometric detectors in three arrays, observing simultaneously at 250, 350, and 500μm. The diffraction-limited optical system provides a resolution of 30"at 250μm. The polarimeter consists of photolithographic polarizing grids mounted in front of each bolometer/ detector array. A rotating 4K achromatic half-wave plate provides additional polarization modulation. With its unprecedented mapping speed and resolution, BLAST-Pol will produce three-color polarization maps for a large number of molecular clouds. The instrument provides a much needed bridge in spatial coverage between larger-scale, coarse resolution surveys and narrow field of view, and high resolution observations of substructure within molecular cloud cores. The first science flight will be from McMurdo Station, Antarctica in December 2010.
TL;DR: In this paper, the authors present an extensive review of the eigenvalue calibration method and an existing variant, and introduce two more variants of the method to calibrate imaging polarimeters that use high numerical aperture optics.
Abstract: Complex polarisation sensitive systems such as imaging Mueller matrix polarimeters are commonly calibrated using the eigenvalue calibration method. In this paper we present an extensive review of the method and an existing variant. We also introduce two more variants of the method to calibrate imaging polarimeters that use high numerical aperture optics. The calibration methods are tested using a Mueller matrix confocal microscope of high numerical aperture, and the effect of the pinhole size on the polarisation is also assessed experimentally.
TL;DR: In this article, a comparison of the information content of full quad-pol data and pseudo-covariance matrix derived from compact polarimetric (CP) SAR modes is presented.
Abstract: Recently, there has been growing interest in dual-pol systems that transmit one polarization and receive two polarizations. Souyris et al. proposed a DP mode called compact polarimetry (CP) which is able to reduce the complexity, cost, mass, and data rate of a SAR system while attempting to maintain many capabilities of a fully polarimetric system. This paper provides a comparison of the information content of full quad-pol data and the pseudo quad-pol data derived from compact polarimetric SAR modes. A pseudo-covariance matrix can be reconstructed following Souyris’s approach and is shown to be similar to the full polarimetric (FP) covariance matrix. Both the polarimetric signatures based on the kennaugh matrix and the Freeman and Durden decomposition in the context of this compact polarimetry mode are explored. The Freeman and Durden decomposition is used in our study because of its direct relationship to the reflection symmetry. We illustrate our results by using the polarimetric SAR images of Algiers city in Algeria acquired by the RadarSAT2 in C-band.
TL;DR: In this paper, the authors developed multi-chroic antenna-coupled Transition Edge Sensor (TES) focal planes for Cosmic Microwave Background (CMB) polarimetry.
Abstract: We are developing multi-chroic antenna-coupled Transition Edge Sensor (TES) focal planes for Cosmic Microwave Background (CMB) polarimetry. In each pixel, a dual polarized sinuous antenna collects light over a two-octave frequency band. Each antenna couples to the telescope with a contacting silicon lens. The antenna couples the broadband RF signal to microstrip transmission lines, and then filter banks split the broadband signal into several frequency bands. A TES bolometer detects the power in each band and polarization. We will describe the design of this device and demonstrate its performance with optical data measured using prototype pixels. Our measurements show low ellipticity beams, low cross-polarization, and properly partitioned bands in banks of 2, 3, and 7 filters. Finally, we will describe how we will upgrade the Polarbear CMB experiment using the focal planes of these detectors to increase the experiment’s mapping speed and its ability to discriminate between the CMB and polarized foregrounds.
TL;DR: In this article, the authors analyzed polarimetric characteristics of ships and ambiguities, and found that backscattering from a ship consisted of a mixture of single-bounced, double-bounce and depolarized or diffused scattering types due to its complex physical structure.
Abstract: Synthetic aperture radar (SAR) imagery from the sea can contain ships and their ambiguities. The ambiguities are visually identifiable due to their high intensities in the low radar backscatter background of sea environments and can be mistaken as ships, resulting in false alarms in ship detection. Analysing polarimetric characteristics of ships and ambiguities, we found that (a) backscattering from a ship consisted of a mixture of single-bounced, double-bounced and depolarized or diffused scattering types due to its complex physical structure; (b) that only a strong single- or double-bounce scatterer produced ambiguities in azimuth that look like relatively strong double- or single-bounce scatterers, respectively; and (c) that eigenvalues corresponding to the single- or double-bounce scattering mechanisms of the ambiguities were high but the eigenvalue corresponding to the depolarized scattering mechanisms of the ambiguities was low. With these findings, we proposed a ship detection method that applies t...
TL;DR: Non-linear support vector machines (SVM) are applied to classify materials over BRDF and show variations in receiver operator characteristic curves with scene composition and number of Mueller matrix channels in the observation.
Abstract: Active (Mueller matrix) remote sensing is an under-utilized technique for material discrimination and classication.
A full Mueller matrix instrument returns more information than a passive (Stokes) polarimeter; Mueller
polarimeters measure depolarization and other linear transformations that materials impart on incident Stokes
vectors, which passive polarimeters cannot measure. This increase in information therefore allows for better
classication of materials (in general). Ideally, material classication over the entire polarized BRDF is desired,
but sets of Mueller matrices for dierent materials are generally not separable by a linear classier over elevation
and azimuthal target angles. We apply non-linear support vector machines (SVM) to classify materials over
BRDF (all relevant angles) and show variations in receiver operator characteristic curves with scene composition
and number of Mueller matrix channels in the observation.
TL;DR: An active imaging, snapshot, system design and postprocessing algorithms that differentiate between radiation that scatters or reflects from remote, obscured objects and the radiation from the scattering media itself through a combination of polarization difference imaging, channel blurring, and Fourier spatial filtering are developed.
Abstract: Conventional intensity imaging through turbid media suffers from rapid loss of image contrast due to light scattering from particles or random variations of refractive index. This paper features the development of an active imaging, snapshot, system design and postprocessing algorithms that differentiate between radiation that scatters or reflects from remote, obscured objects and the radiation from the scattering media itself through a combination of polarization difference imaging, channel blurring, and Fourier spatial filtering. The produced sensor acquires and processes image data in real time, yielding improved image contrasts by factors of 10 or greater for dense water vapor obscurants.
TL;DR: This paper shows how compact polarimetric data simulated from RADARSAT-2 quad-pol imagery can be used for iceberg detection using the likelihood ratio test method, and shows that use of the pseudo-quad-pol HV intensity can augment the detection performance of a compact polarIMetric SAR system.
Abstract: In recent years, the use of synthetic aperture radar (SAR) for iceberg detection has been increasing thanks to the greater availability and coverage of SAR data, particularly polarimetric data. Greater amounts of polarimetric information can increase detection performance, preventing false alarms and missed detections. However, quad-polarization (quad-pol) SAR systems have increased data rate and power usage requirements, causing quad-pol modes to have generally half the swath width of dual-polarization (dual-pol) modes. Compact polarimetry is a compromise that allows the approximation of quad-pol information (referred to as “pseudo quad-pol”) using a dual-pol SAR. In this paper, using compact polarimetric data simulated from RADARSAT-2 quad-pol imagery, we show how pseudo-quad-pol data can be used for iceberg detection using the likelihood ratio test method. We show that use of the pseudo-quad-pol HV intensity can augment the detection performance of a compact polarimetric SAR system. We also compare the...
TL;DR: The carrier frequency is two times higher than that of the snapshot imaging polarimeter using two conventional Savart polariscopes and the signal-to-noise ratio and the spatial resolution of imagery in each channel are improved due to the increase of the carrier frequency when the authors filter the channels to recover the Stokes vector images.
Abstract: In this paper, based on the combination of two modified Savart polariscopes, we present a snapshot imaging polarimeter and show that the carrier frequency is two times higher than that of the snapshot imaging polarimeter using two conventional Savart polariscopes. The signal-to-noise ratio and the spatial resolution of imagery in each channel are improved due to the increase of the carrier frequency when we filter the channels to recover the Stokes vector images. Moreover, compared with conventional imaging polarimetry, the remarkable advantage of the proposed instrument is that it is also simple, compact, miniature, snapshotted, and static (no moving parts). To demonstrate the feasibility of the proposed snapshot imaging polarimeter, the numerical simulation of a design example is presented in detail.
TL;DR: In this paper, the authors assess the polarimetric performance of two commonly used calibration methods that exploit unpolarized calibration sources, and demonstrate that the sensitivity loss can be limited to 4.5% and that the polarIMetric performance over the wide field-of-view (FoV) is close to the best achievable performance.
Abstract: Polarimetric phased arrays require a calibration method that allows the system to measure the polarization state of the received signals. In this paper, we assess the polarimetric performance of two commonly used calibration methods that exploit unpolarized calibration sources. The first method obtains a polarimetrically calibrated beamforming solution from the two dominant eigenvectors of the measured signal covariance matrix. We demonstrate that this method is sensitivity equivalent to the theoretical optimal method, but suffers from an ambiguity that has to be resolved by additional measurements on (partially) polarized sources or by exploiting the intrinsic polarimetric quality of the antenna system. The easy-to-implement bi-scalar approach assumes that the feed system consists of two sets of orthogonally oriented antenna elements, each associated with one polarization. We assess its sensitivity and polarimetric performance over a wide field-of-view (FoV) using simulations of a phased array feed system for the Westerbork Synthesis Radio Telescope. Our results indicate that the sensitivity loss can be limited to 4.5% and that the polarimetric performance over the FoV is close to the best achievable performance. The latter implies that the intrinsic polarimetric quality of the antennas remains a crucial factor despite the development of novel polarimetric calibration methods.