Showing papers on "Polarimetry published in 2007"
01 Apr 2007
TL;DR: In this article, the Mauna Kea Observatories near-infrared (1-5 µm) set has been promoted among instrument groups throughcombined filter production runs.
Abstract: . The proliferation of near-infrared (1–5 µm) photometric systemsover the last 30 years has made the comparison of photometric results difficult.In an effort to standardize infrared filters in use, the Mauna Kea Observatoriesnear-infrared filter set has been promoted among instrument groups throughcombined filter production runs. The characteristics of this filter set are sum-marized, and some aspects of the filter wavelength definitions, the flux densityfor zero magnitude, atmospheric extinction coefficients, and color correction toabove the atmosphere are discussed. 1. IntroductionThe foundations of modern infrared photometry at near-infrared wavelengths(1–5 µm) were built upon the pioneering work of Johnson and his collaborators(Johnson 1966; Johnson et al. 1966; Johnson, MacArthur, & Mitchell 1968).The near-infrared filters used in these early works were very broad, and theatmospheric absorption bands defined the effective widths of the filters. Thefilter profiles used by Johnson (1965) are shown in Fig. 1, which demonstratesthat the deep atmospheric absorption bands (mostly due to water vapor) playa significant role in determining the effective transmission of the atmosphere +telescope + filter observational system.The problem with allowing the atmosphere to define the passband is thatthe atmosphere varies substantially from place to place and, at any given loca-tion, from night to night (even from hour to hour). Hence, the reproducibility ofphotometricobservationsandconversionstootherphotometricsystems becomesdifficult or impossible to achieve. To prevent these problems, the photometricbands should ideally be defined by only the filter transmission profiles (if possi-ble). Ideally, the filter bandpasses should avoid deep telluric absorption featuresand any part of the telluric spectrum that has a large first derivative and/or ishighly variable. In principle, filter properties can be controlled by the manufac-turer, and so the specifications and characteristics of the filters are usually theonly aspect of the observational system that can remain constant from instru-ment to instrument and site to site. If such a set of filters were easily replicableand distributed to a large number of observatories, the comparison of photomet-409
248 citations
01 Apr 2007
TL;DR: In this paper, the authors present a preliminary catalog for the OmegaCAM wide field imager, which is used to bootstrap the construction of the secondary standards catalog for 8 Landolt equatorial fields.
Abstract: The OmegaCAM wide-field imager will start operations at the ESO VLT Survey Telescope at Paranal in 2007. The photometric calibration of OmegaCAM data depends on standard-star measurements that cover the complete 1 × 1 FoV of OmegeaCAM. A catalog fullfilling this requirement for 8 Landolt equatorial fields, denoted the OmegaCAM Secondary Standards Catalog, will be constructed from OmegaCAM observations during the first year of operations. Here we present the ‘Preliminary Catalog’ which will be used to bootstrap the construction of the OmegaCAM Secondary Standards Catalog. Thus the Preliminary Catalog will be used to assess the performance of OmegaCAM+VST early-on. The catalog is based on WFC data from the INT.
197 citations
01 Sep 2007-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a sealed Gas Pixel Detector (GPD) has been proposed for X-ray polarimetry, which is the last unexplored field of Xray astronomy, and it is able to simultaneously perform good imaging (50-60μm), moderate spectroscopy (∼15% at 6-kV) as well as fast, high-rate timing in the 1-10kV range.
Abstract: We report on the results of a new, sealed Gas Pixel Detector. The very compact design and the absence of the gas flow system make this detector substantially ready for use as focal plane detector for future X-ray space telescopes. The instrument brings high sensitivity to X-ray polarimetry, which is the last unexplored field of X-ray astronomy. It derives the polarization information from the track of the photoelectrons that are imaged by a high-gain (>1000), fine pitch GEM that matches the pitch of a pixel ASIC which is the collecting anode of the GPD (105k, 50 μm wide, hexagonal cells). The device is able to simultaneously perform good imaging (50–60 μm), moderate spectroscopy (∼15% at 6 keV) as well as fast, high-rate timing in the 1–10 keV range. Moreover, being truly 2D, it is non-dispersive and does not require any rotation. The great improvement of sensitivity, at least two orders of magnitude with respect to traditional polarimeters (based on Bragg crystals or Thomson scattering), will allow the direct exploration of the most dramatic objects of the X-ray sky. At the focus of the large mirror area of the XEUS telescope it will be decisive in reaching many of the scientific goals of the mission. With integration times of the order of 1 day, polarimetry of Active Galactic Nuclei at the percent level will be possible, making for a real breakthrough in high-energy astrophysics.
122 citations
TL;DR: Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements and laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angles.
Abstract: A passive-polarization-based imaging system records the polarization state of light reflected by objects that are illuminated with an unpolarized and generally uncontrolled source. Such systems can be useful in many remote sensing applications including target detection, object segmentation, and material classification. We present a method to jointly estimate the complex index of refraction and the reflection angle (reflected zenith angle) of a target from multiple measurements collected by a passive polarimeter. An expression for the degree of polarization is derived from the microfacet polarimetric bidirectional reflectance model for the case of scattering in the plane of incidence. Using this expression, we develop a nonlinear least-squares estimation algorithm for extracting an apparent index of refraction and the reflection angle from a set of polarization measurements collected from multiple source positions. Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements. Laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angle.
109 citations
TL;DR: A time domain THz polarimetry method with three wire grid polarizers is developed and obtained the isotropic polarization rotation of a terahertz wave free from the birefringence of the structures.
Abstract: We propose and demonstrate polarization rotation of a terahertz (THz) electromagnetic wave by using two-dimensional gratings consisting of two displaced layers of gold film with complimentary chiral patterns with four-fold symmetry. We develop a time domain THz polarimetry method with three wire grid polarizers and distinguish optical activity from optical anisotropy. We obtain the isotropic polarization rotation of a terahertz wave free from the birefringence of the structures. Results indicate the possibility of controlling THz polarization with artificial chiral structures fabricated with thin metal films.
109 citations
TL;DR: A dual-photoelastic-modulator- (PEM-) based spectropolarimetric camera concept is presented as an approach for global aerosol monitoring from space to measure degree of linear polarization with an uncertainty of less than 0.5% in multiple spectral bands.
Abstract: A dual-photoelastic-modulator- (PEM-) based spectropolarimetric camera concept is presented as an approach for global aerosol monitoring from space. The most challenging performance objective is to measure degree of linear polarization (DOLP) with an uncertainty of less than 0.5% in multiple spectral bands, at moderately high spatial resolution, over a wide field of view, and for the duration of a multiyear mission. To achieve this, the tandem PEMs are operated as an electro-optic circular retardance modulator within a high-performance reflective imaging system. Operating the PEMs at slightly different resonant frequencies generates a beat signal that modulates the polarized component of the incident light at a much lower heterodyne frequency. The Stokes parameter ratio q = Q/I is obtained from measurements acquired from each pixel during a single frame, providing insensitivity to pixel responsivity drift and minimizing polarization artifacts that conventionally arise when this quantity is derived from differences in the signals from separate detectors. Similarly, u = U/I is obtained from a different pixel; q and u are then combined to form the DOLP. A detailed accuracy and tolerance analysis for this polarimeter is presented.
107 citations
TL;DR: In this paper, the authors present examples of strong depolarization in oriented crystals from the data collected by the polarimetric prototype of TSPARQL, which is used for dual-polarization weather radar.
Abstract: Simultaneous transmission and reception of horizontally and vertically polarized waves is a preferable choice technique for dual-polarization weather radar. One of the consequences of such a choice is possible cross-coupling between orthogonally polarized waves. Cross-coupling depends on depolarizing properties of propagation media, and it is usually negligible in rain because the net mean canting angle of raindrops is close to zero. Snow crystals at the tops of thunderstorm clouds are often canted in the presence of strong electric fields and produce noticeable cross-coupling between radar signals at horizontal and vertical polarizations if both signals are transmitted and received simultaneously. As a result, peculiar-looking radial signatures of differential reflectivity ZDR and differential phase ΦDP are commonly observed in the crystal regions of thunderstorms. The paper presents examples of strong depolarization in oriented crystals from the data collected by the polarimetric prototype of t...
90 citations
TL;DR: In this article, the authors examined the partial polarization of focused light and demonstrated that the focusing of unpolarized light results in rings of full polarization in the focal plane of the focusing optics.
Abstract: The polarization of light is important in a great variety of optical phenomena, ranging from transmission, reflection and scattering to polarimetric imaging of scenes and quantum-mechanical selection rules of atomic and molecular transitions. Among some less-well-known phenomena that illustrate the vectorial nature of light are the Pancharatnam1 (or geometric2) phase, singularities in the polarization pattern of clear sky3 and polarization of microwave background radiation4. Here, we examine the partial polarization of focused light. We experimentally demonstrate a rather surprising phenomenon, where the focusing of unpolarized light results in rings of full polarization in the focal plane of the focusing optics. The polarization rings are imaged with a resolution of <100 nm by probing the focal region using a gold nanoparticle.
83 citations
TL;DR: A polarimetric imaging method of a 3D object by use of on-axis phase-shifting digital holography is presented, which results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves.
Abstract: A polarimetric imaging method of a 3D object by use of on-axis phase-shifting digital holography is presented. The polarimetric image results from a combination of two kinds of holographic imaging using orthogonal polarized reference waves. Experimental demonstration of a 3D polarimetric imaging is presented.
74 citations
TL;DR: In this paper, a large-aperture, electromagnetic model for coherent microscopy is presented and the inverse scattering problem is solved and an image-reconstruction algorithm consistent with interferometric synthetic aperture microscopy (ISAM) is presented.
Abstract: A large-aperture, electromagnetic model for coherent microscopy is presented and the inverse scattering problem is solved. Approximations to the model are developed for near-focus and far-from-focus operations. These approximations result in an image-reconstruction algorithm consistent with interferometric synthetic aperture microscopy (ISAM): this validates ISAM processing of optical-coherence-tomography and optical-coherence-microscopy data in a vectorial setting. Numerical simulations confirm that diffraction-limited resolution can be achieved outside the focal plane and that depth of focus is limited only by measurement noise and/or detector dynamic range. Furthermore, the model presented is suitable for the quantitative study of polarimetric coherent microscopy systems operating within the first Born approximation.
63 citations
TL;DR: In this paper, the first generation of bolometric cosmic microwave background (cmb) polarimeters are described in detail and the design, characterization, and analysis of data obtained using Polarization Sensitive Bolometers (PSBs) are described.
Abstract: Aims. We discuss instrumental and analytic methods that have been developed for the first generation of bolometric cosmic microwave background (cmb) polarimeters. The design, characterization, and analysis of data obtained using Polarization Sensitive Bolometers (PSBs) are described in detail. This is followed by a brief study of the effect of various polarization modulation techniques on the recovery of sky polarization from scanning polarimeter data. Methods. Having been successfully implemented on the sub-orbital Boomerang experiment, PSBs are currently operational in two terrestrial cmb polarization experiments (Quad and the Robinson Telescope). We investigate two approaches to the analysis of data from these experiments, using realistic simulations of time ordered data to illustrate the impact of instrumental effects on the fidelity of the recovered polarization signal. Results. We find that the analysis of difference time streams takes full advantage of the high degree of common mode rejection afforded by the PSB design. In addition to the observational efforts currently underway, this discussion is directly applicable to the PSBs that constitute the polarized capability of the Planck HFI instrument.
TL;DR: In this article, a prominent and extended polarized nebula over NGC 2024 was found and constrained the location of the illuminating source of the nebula through the analysis of polarization vectors, where a massive star, IRS 2b, is located in the center of the symmetric vector pattern.
Abstract: We conducted wide-field JHKs imaging polarimetry toward NGC 2024. We found a prominent and extended polarized nebula over NGC 2024, and constrained the location of illuminating source of the nebula through the analysis of polarization vectors. A massive star, IRS 2b, is located in the center of the symmetric vector pattern. Five small polarized nebulae associated with YSOs are discovered on our polarization images. These nebulae are responsible for the structures of circumstellar matter that produce strongly polarized light through dust scattering. For the point-like sources, we performed software aperture polarimetry in order to measure integrated polarizations, and found five young brown dwarfs with highly polarized integrated emission. These sources serve as direct evidence for the existence of disk/envelope system around brown dwarfs. We investigated the magnetic field structure of NGC 2024 through the measurements of dichroic polarization. The average position angle of projected magnetic fields across the region is found to be 110 degrees. We found a good consistency in magnetic field structures obtained using near-infrared dichroic polarization and sub-mm/far-infrared dust emission polarization, indicating that the dichroic polarizations at near-infrared wavelengths trace magnetic field structures inside dense molecular clouds.
15 Nov 2007
TL;DR: The Glory mission Aerosol Polarimetry Sensor (APS) was built by Raytheon under contract to NASA's Goddard Space Flight Center in late 2008 to determine the global distribution of aerosols and clouds with sufficient accuracy and coverage.
Abstract: This paper describes the Glory Mission Aerosol Polarimetry Sensor (APS) being built by Raytheon under contract to
NASA's Goddard Space Flight Center Scheduled for launch in late 2008, the instrument is part of the US Climate
Change Research Initiative to determine the global distribution of aerosols and clouds with sufficient accuracy and
coverage to establish the aerosol effects on global climate change as well as begin a precise long-term aerosol record
The Glory APS is a polarimeter with nine solar reflectance spectral bands that measure the first three Stokes parameters
vector components for a total of 27 unique measurements In order to improve the reliability and accuracy of the
measurements, additional 9 redundant measurements are made, yielding a total of 36 channels The sensor is designed
to acquire spatial, temporal, and spectral measurements simultaneously to minimize instrumental effects and provide
extremely accurate Raw Data Records The APS scans in the direction close to of the spacecraft velocity vector in
order to acquire multi-angle samples for each retrieval location so that the Stokes parameters can be measured as
functions of view angle
TL;DR: A new radar primitive is described that enables instantaneous radar polarimetry at essentially no increase in signal processing complexity and avoids the information loss inherent in single-channel matched filters.
Abstract: This paper describes a new radar primitive that enables instantaneous radar polarimetry at essentially no increase in signal processing complexity This primitive coordinates transmission of distinct waveforms on orthogonal polarizations and applies a unitary matched filter bank on receive This avoids the information loss inherent in single-channel matched filters A further advantage of this scheme is the elimination of range sidelobes
11 May 2007-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a large area polarized 3He neutron spin filter has been developed and tested in long-term operation, and the resulting neutron polarization and transmission are velocity dependent and are optimized for 5 A.
Abstract: A large area polarized 3He neutron spin filter has been developed and tested in long-term operation. The polarizer cells have area 50 cm2 and larger allowing access to a large area neutron beam. Polarization of 3He up to 57 ± 1 % was measured by monitoring the neutron transmission through the 3He. The polarization was maintained over the course of several weeks, but the maximum attainable polarization declined over the course of a year-long run as the cell degraded, possibly due to long-term exposure to the neutron beam at high temperatures. The resulting neutron polarization and transmission are velocity dependent and are optimized for 5 A. Cell construction, polarizer design, performance, and polarimetry are described in this paper.
TL;DR: A method for calibrating a polarization state analyzer that uses a set of well- characterized reference polarization states and makes no assumptions about the optics contained in the polarimeter other than their linearity is presented.
Abstract: We present a method for calibrating a polarization state analyzer that uses a set of well- characterized reference polarization states and makes no assumptions about the optics contained in the polarimeter other than their linearity. The method requires that a matrix be constructed that contains the data acquired for each of the reference polarization states and that this matrix be pseudoinverted. Since this matrix is usually singular, we improve the method by performing the pseudoinversion by singular value decomposition, keeping only the four largest singular values. We demonstrate the calibration technique using an imaging polarimeter based upon liquid crystal variable retarders and with light emitting diode (LED) illumination centered at 472 nm, 525 nm, and 630 nm. We generate the reference polarization states by using an unpolarized source, a single polarizer, and a Fresnel rhomb. This method is particularly useful when calibrations are performed on field-grade instruments at a centrally maintained facility and when a traceability chain needs to be maintained.
TL;DR: In this paper, the authors presented diffraction-limited, 10 μm imaging polarimetry data for the central regions of the archetypal Seyfert active galactic nucleus NGC 1068.
Abstract: We present diffraction-limited, 10 μm imaging polarimetry data for the central regions of the archetypal Seyfert active galactic nucleus NGC 1068. The position angle of polarization is consistent with three dominant polarizing mechanisms. We identify three distinct regions of polarization: (1) north of the nucleus, arising from aligned dust in the narrow emission line region, (2) south, east, and west of the nucleus, consistent with dust being channeled toward the central engine, and (3) a central minimum of polarization consistent with a compact (≤22 pc) torus. These observations provide continuity between the geometrically and optically thick torus and the host galaxy's nuclear environments. These images represent the first published mid-IR polarimetry from an 8 m-class telescope and illustrate the potential of such observations.
TL;DR: The High-resolution Airborne Wideband Camera (HAWC) is a 12 32 pixel bolometer camera designed to cover the 53 { 215 m spectral range in 4 colors, all at diractionlimite d resolution (5 { 21 arcsec).
Abstract: Multi-wavelength imaging polarimetry at far-infrared wavelengths has proven to be an excellent tool for studying the physical properties of dust, molecular clouds, and magnetic elds in the interstellar medium. Although these wavelengths are only observable from airborne or space-based platforms, no rst-generation instrument for the Stratospheric Observatory for Infrared Astronomy (SOFIA) is presently designed with polarimetric capabilities. We study several options for upgrading the High-resolution Airborne Wideband Camera (HAWC) to a sensitive FIR polarimeter. HAWC is a 12 32 pixel bolometer camera designed to cover the 53 { 215 m spectral range in 4 colors, all at diraction-limite d resolution (5 { 21 arcsec). Upgrade options include: (1) an external set of optics which modulates the polarization state of the incoming radiation before entering the cryostat window; (2) internal polarizing optics; and (3) a replacement of the current detector array with two state-of-the-art superconducting bolometer arrays, an upgrade of the HAWC camera as well as polarimeter. We discuss a range of science studies which will be possible with these upgrades including magnetic elds in star-forming regions and galaxies and the wavelength-dependence of polarization.
TL;DR: This paper explores the nature of bistatic radar scattering from terrain by reporting the results of an investigation involving measurements of the hemispherical pattern of the field scattered by a random soil surface.
Abstract: This paper explores the nature of bistatic radar scattering from terrain by reporting the results of an investigation involving measurements of the hemispherical pattern of the field scattered by a random soil surface. The measurements were performed by a 35-GHz fully polarimetric radar system with transmitter and receiver modules mounted on separate rotatable arches. The acquired data were analyzed to determine the angular sensitivities of several attributes of the scattered field, including amplitudes and phase differences of the polarized scattering coefficients, and their copolarized and cross-polarized ratios. Generally speaking, the scattering pattern exhibits a weak dependence on the scattering angle thetass (except along the backward direction and forward specular direction), but it exhibits a strong dependence on the azimuth angle phi, particularly for the cross-polarized components. Much of the dependence is attributed to the vectorial definition of polarization in a standard frame of reference. Comparison of the measured data with calculations based on the second-order physical optics model reveals reasonable overall agreement between theory and observations (typically within 4 dB)
TL;DR: In this paper, an extension of the basic paradigm is presented and worked out in some detail for accurate optical and IR polarimetry using the Nasmyth focus in large modern facilities.
Abstract: The classical prescription for accurate optical and IR polarimetry is the following: a weakly polarizing telescope, a polarization modulator, imager/disperser optics, and a demodulating detector. This list needs to be modified when one is forced to use the Nasmyth focus, as often happens in large modern facilities. An extension of the basic paradigm is presented here and worked out in some detail.
TL;DR: A novel method for the spectropolarimetric measurement of materials using the channeled spectrum that is less susceptible to the sample-induced fluctuations of the wavefront or ray-direction and can offer the same information about the sample as has been obtained by the previous method.
Abstract: A novel method for the spectropolarimetric measurement of materials using the channeled spectrum is described. A pair of high order retarders are incorporated into the illuminating optics of a broadband spectropolarimeter, so that the sample under measurement is illuminated with the light that is modulated in the spectral-dependence of its polarization. The Fourier analysis of the channeled spectrum obtained from the spectropolarimeter allows determining the four spectrally-resolved polarimetric parameters of the sample simultaneously. This approach has a feature that it requires neither mechanically- nor electrically-controllable components for polarization modulation, similar to the previous method for the channeled spectropolarimetry in which the high-order retarders are placed in the receiving optics. The new method can offer the same information about the sample as has been obtained by the previous method, provided that all the optical components satisfy the principle of reciprocity. Furthermore, the new method has an additional advantage over the previous method that it is less susceptible to the sample-induced fluctuations of the wavefront or ray-direction. The effectiveness of this method is experimentally demonstrated with the measurement of a birefringent sample.
TL;DR: In this article, the Stokes vector is used to describe the evolution of a paraxial electromagnetic wave propagating in a weakly anisotropic medium and characterizing by a non-uniform polarization distribution with polarization singularities.
Abstract: We describe evolution of a paraxial electromagnetic wave propagating in a weakly anisotropic medium and characterizing by a non-uniform polarization distribution with polarization singularities. Our approach is based on the evolution equation for the Stokes vector, well-approved in classical polarimetry, but supplied now with a non-uniform initial distribution of the polarization field. In the case of homogeneous anisotropic medium, the equation is integrated analytically, which yields a 3-dimensional distribution of the polarization parameters, including singularities, i.e. C-lines of circular polarization and L-surfaces of linear polarization. The general theory is illustrated by specific examples of the unfolding of a vectorial vortex in birefringent and dichroic media.
TL;DR: In this paper, the relationship between real and imaginary parts of the complex polarization angle and polarization ellipse parameters is established, which governs the evolution of the polarization along the curvilinear ray.
TL;DR: In this article, a MuPAD (Mu-metal polarization analysis device) based on a zero-field environment produced by highly permeable mu-metal is presented, which can perform routine SNP measurements at finite scattering angles.
Abstract: Over the last decade, the systematic application of spherical neutron polarmetry (SNP) has been successfully used to investigate scientific questions which were intractable before, e.g. study of magneto-electric crystals such as LiCoPO 4 and MnGeO 3 . Until now, the only device capable of performing routine SNP measurements at finite scattering angles was CryoPAD (cryogenic polarization analysis device), presented by Tasset et al. in 1989. Recently we demonstrated that an alternative setup named MuPAD (Mu-metal polarization analysis device) based on a zero-field environment produced by highly permeable mu-metal is also feasible. Here we present this new SNP device together with some first results.
TL;DR: In this article, the authors presented diffraction limited, 10um imaging polarimetry data for the central regions of the archetypal Seyfert AGN, NGC1068.
Abstract: We present diffraction limited, 10um imaging polarimetry data for the central regions of the archetypal Seyfert AGN, NGC1068. The position angle of polarization is consistent with three dominant polarizing mechanisms. We identify three distinct regions of polarization: (a) north of the nucleus, arising from aligned dust in the NLR, (b) south, east and west of the nucleus, consistent with dust being channeled toward the central engine and (c) a central minimum of polarization consistent with a compact (<22pc) torus. These observations provide continuity between the geometrically and optically thick torus and the host galaxy's nuclear environments. These images represent the first published mid-IR polarimetry from an 8-m class telescope and illustrate the potential of such observations.
TL;DR: The results of experiments in developing a method for extracting three-dimensional information from a scene by means of a polarimetric passive imaging sensor, which provides a full Stokes vector at each sensor pixel location, are summarized.
Abstract: The results of experiments in developing a method for extracting three-dimensional information from a scene by means of a polarimetric passive imaging sensor are summarized. This sensor provides a full Stokes vector at each sensor pixel location from which degree and angle of linear polarization are computed. The angle of linear polarization provides the azimuth angle of the surface normal vector. The depression angle of this surface normal vector is obtained in terms of the emitting object's index of refraction from the solution of an equation derived from Fresnel equations, Snell's law, and percent of linear polarization. Results of the application of this approach to simulated infrared polarimetric data are provided.
TL;DR: This paper utilizes a 2-D polarimetric linear prediction model and expands the spatial frequency bandwidth in range and azimuth directions simultaneously and shows the performance of the 2D-PBWE through a simulated radar image and a real polarimetry SAR image.
Abstract: The resolution of a synthetic aperture radar (SAR) image, in range and azimuth, is determined by the transmitted bandwidth and the synthetic aperture length, respectively. Various superresolution techniques for improving resolution have been proposed, and we have proposed an algorithm that we call polarimetric bandwidth extrapolation (PBWE). To apply PBWE to a radar image, one needs to first apply PBWE in the range direction and then in the azimuth direction, or vice versa . In this paper, PBWE is further extended to the 2-D case. This extended case (2D-PBWE) utilizes a 2-D polarimetric linear prediction model and expands the spatial frequency bandwidth in range and azimuth directions simultaneously. The performance of the 2D-PBWE is shown through a simulated radar image and a real polarimetric SAR image
TL;DR: In this article, the structure of the kpc-scale jet in the nearby radio galaxy 3C 15, using new optical Hubble Space Telescope (HST) ACS/F606W polarimetry together with archival multi-band HST imaging, Chandra X-ray data and 8.4 GHz VLA radio polarimetric.
Abstract: We investigate the structure of the kpc-scale jet in the nearby (z = 0.073) radio galaxy 3C 15, using new optical Hubble Space Telescope (HST) ACS/F606W polarimetry together with archival multi-band HST imaging, Chandra X-ray data and 8.4 GHz VLA radio polarimetry. The new data confirm that synchrotron radiation dominates in the optical. With matched beams, the jet is generally narrower in the optical than in the radio, suggesting a stratified flow. We examine a simple two-component model comprising a highly relativistic spine and lower-velocity sheath. This configuration is broadly consistent with polarization angle differences seen in the optical and radio data. The base of the jet is relatively brighter in the ultraviolet and X-ray than at lower energies, and the radio and optical polarization angles vary significantly as the jet brightens downstream. Further out, the X-ray intensity rises again and the apparent magnetic field becomes simpler, indicating a strong shock. Modelling the synchrotron spectrum of this brightest X-ray knot provides an estimate of its minimum internal pressure, and a comparison with the thermal pressure from X-ray emitting gas shows that the knot is overpressured and likely to be a temporary, expanding feature.
TL;DR: The High-resolution Airborne Wideband Camera (HAWC) as discussed by the authors is a 12 x 32 pixel bolometer camera designed to cover the 53 - 215 micron spectral range in 4 colors, all at diffraction-limited resolution (5 - 21 arcsec).
Abstract: Multi-wavelength imaging polarimetry at far-infrared wavelengths has proven to be an excellent tool for studying the physical properties of dust, molecular clouds, and magnetic fields in the interstellar medium. Although these wavelengths are only observable from airborne or space-based platforms, no first-generation instrument for the Stratospheric Observatory for Infrared Astronomy (SOFIA) is presently designed with polarimetric capabilities. We study several options for upgrading the High-resolution Airborne Wideband Camera (HAWC) to a sensitive FIR polarimeter. HAWC is a 12 x 32 pixel bolometer camera designed to cover the 53 - 215 micron spectral range in 4 colors, all at diffraction-limited resolution (5 - 21 arcsec). Upgrade options include: (1) an external set of optics which modulates the polarization state of the incoming radiation before entering the cryostat window; (2) internal polarizing optics; and (3) a replacement of the current detector array with two state-of-the-art superconducting bolometer arrays, an upgrade of the HAWC camera as well as polarimeter. We discuss a range of science studies which will be possible with these upgrades including magnetic fields in star-forming regions and galaxies and the wavelength-dependence of polarization.
TL;DR: In this article, the authors used imaging polarimetry taken with the HST Advanced Camera for Surveys High Resolution Camera to explore the three-dimensional structure of the circumstellar dust distribution around the red supergiant VY Canis Majoris.
Abstract: We use imaging polarimetry taken with the HST Advanced Camera for Surveys High Resolution Camera to explore the three-dimensional structure of the circumstellar dust distribution around the red supergiant VY Canis Majoris. The polarization vectors of the nebulosity surrounding VY CMa show a strong centrosymmetric pattern in all directions except directly east and range from 10% to 80% in fractional polarization. In regions that are optically thin, and therefore likely to have only single scattering, we use the fractional polarization and photometric color to locate the physical position of the dust along the line of sight. Most of the individual arclike features and clumps seen in the intensity image are also features in the fractional polarization map. These features must be distinct geometric objects. If they were just local density enhancements, the fractional polarization would not change so abruptly at the edge of the feature. The location of these features in the ejecta of VY CMa using polarimetry provides a determination of their three-dimensional geometry independent of, but in close agreement with, the results from our study of their kinematics (Paper I).