Showing papers on "Polarimetry published in 2014"

Polarisation: Applications In Remote Sensing

Abstract: 1. Polarised Electromagnetic Waves 2. Depolarisation and Scattering Entropy 3. Depolarisation in Surface and Volume Scattering 4. Decomposition Theorems 5. Introduction to Radar Interferometry 6. Polarimetric Interferometry 7. Coherence Variation for Surface and Volume Scattering 8. Parameter Estimation using Polarimetric Interferometry 9. Applications of Polarimetry and Interferometry Appendix 1: Introduction to Matrix Algebra Appendix 2: Unitary and Rotation Groups Appendix 3: Coherent Stochastic Signal Analysis

Fully Polarimetric High-Resolution 3-D Imaging With Circular SAR at L-Band

Abstract: This paper presents the first fully polarimetric high-resolution circular synthetic aperture radar (CSAR) images at L-band (1.3 GHz). The circular data were acquired in 2008 by the Experimental SAR (E-SAR) airborne system of the German Aerospace Center (DLR) over the airport of Kaufbeuren, Germany. The obtained images resulting from the coherent integration of the whole circular flight are investigated and discussed in terms of two of the main CSAR properties, namely, the theoretical subwavelength resolution in the horizontal plane (x, y) and the 3-D imaging capabilities. The 3-D imaging capabilities are of special interest due to the penetration of L-band in vegetated areas. These results were compared with images processed by the incoherent addition of the full synthetic aperture. The coherent approach showed a better performance since scatterers are focused at their maximum resolution. Due to the nonlinearity of the tracks and the high-computational burden, an efficient fast factorized back-projection (FFBP) has been developed. Unlike frequencydomain processors, it accommodates azimuthal variances and topography changes. Limits and considerations of the proposed algorithm are described and discussed. To further accelerate this process, the FFBP was also implemented in a graphics processing unit (GPU). Processing performance has been assessed with the direct BP (DBP) as a reference, obtaining speedup factors up to 1800. Residual motion errors have been estimated with a new frequency-based autofocus approach for CSAR configurations based on low signal-to-clutter ratio (SCR) isotropic scatterers. High-resolution images of man-made and distributed scatterers have been analyzed and compared with a stripmap SAR, both concerning anisotropic and isotropic-like scatterers. Results include a single-channel tomogram of a Luneburg lens and a fully polarimetric tomogram of a tree.

Modeling and Interpretation of Scattering Mechanisms in Polarimetric Synthetic Aperture Radar: Advances and perspectives

Abstract: Polarimetric target decomposition is a powerful technique to interpret scattering mechanisms in polarimetric synthetic aperture radar (PolSAR) data. Eigenvalue-?eigenvector-based and model-based methods are two main categories within the incoherent decomposition techniques. Eigenvalue-eigenvector-based decomposition becomes relatively mature since it has a clearer mathematical background and has only one decomposition solution. In contrast, model-based decompositions can obtain different decomposition solutions in terms of various scattering models. Meanwhile, conventional methods with models or assumptions that do not fit the observations may induce deficiencies. Thereby, the development of effective model-based decompositions has received considerable attention and many advances have been reported. This article aims to provide a review for these notable advances, mainly including the incorporation of orientation compensation processing, nonnegative eigenvalue constraint, generalized scattering models, complete information utilization, full-parameter inversion schemes, and fusion of polarimetry and interferometry. Airborne Pi-SAR data sets are used for demonstration. Besides, natural disaster damage evaluation using model-based decomposition is carried out based on advanced land-observing satellite/phased array type L-band synthetic aperture radar (ALOS/PALSAR) data. Finally, further development perspectives are presented and discussed.

Polarimetry with the Gemini Planet Imager: Methods, Performance at First Light, and the Circumstellar Ring around HR 4796A

Abstract: We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point spread function subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side >9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.

Evanescent-wave and ambient chiral sensing by signal-reversing cavity ringdown polarimetry

Abstract: By passing light through a chiral sample — here vapours and solutions — in a specially designed ring cavity, the resulting chiral signals can be isolated from the achiral backgrounds and enhanced by a factor of more than 1,000, making them detectable in situations where conventional means of measurement fail. Detecting and quantifying chirality is important in fields ranging from analytical and biological chemistry to pharmacology and fundamental physics. It is usually done by measuring circular dichroism or optical rotation, procedures that are simple to do in principle but often limited by low signal strength against a large and fluctuating background. Dimitris Sofikitis et al. now show that chiral signals can be selectively enhanced over their background by passing them through a specially designed ring cavity more than a thousand times. With further optimization, the method should exceed current chiral detection limits by several orders of magnitude, an advance that could transform chiral sensing in many fields. Detecting and quantifying chirality is important in fields ranging from analytical and biological chemistry to pharmacology1 and fundamental physics2: it can aid drug design and synthesis, contribute to protein structure determination, and help detect parity violation of the weak force. Recent developments employ microwaves3, femtosecond pulses4, superchiral light5 or photoionization6 to determine chirality, yet the most widely used methods remain the traditional methods of measuring circular dichroism and optical rotation. However, these signals are typically very weak against larger time-dependent backgrounds7. Cavity-enhanced optical methods can be used to amplify weak signals by passing them repeatedly through an optical cavity, and two-mirror cavities achieving up to 105 cavity passes have enabled absorption and birefringence measurements with record sensitivities8,9,10. But chiral signals cancel when passing back and forth through a cavity, while the ubiquitous spurious linear birefringence background is enhanced. Even when intracavity optics overcome these problems11,12,13,14,15, absolute chirality measurements remain difficult and sometimes impossible. Here we use a pulsed-laser bowtie cavity ringdown polarimeter with counter-propagating beams16,17 to enhance chiral signals by a factor equal to the number of cavity passes (typically >103); to suppress the effects of linear birefringence by means of a large induced intracavity Faraday rotation; and to effect rapid signal reversals by reversing the Faraday rotation and subtracting signals from the counter-propagating beams. These features allow absolute chiral signal measurements in environments where background subtraction is not feasible: we determine optical rotation from α-pinene vapour in open air, and from maltodextrin and fructose solutions in the evanescent wave produced by total internal reflection at a prism surface. The limits of the present polarimeter, when using a continuous-wave laser locked to a stable, high-finesse cavity, should match the sensitivity of linear birefringence measurements8 (3 × 10−13 radians), which is several orders of magnitude more sensitive than current chiral detection limits7,14,15 and is expected to transform chiral sensing in many fields.

BICEP3: a 95GHz refracting telescope for degree-scale CMB polarization

Abstract: Bicep3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz. It adopts the methodology of Bicep1, Bicep2 and the Keck Array experiments | it possesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, Bicep3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5x larger than a Bicep2/Keck Array receiver and faster optics (f=1:6 vs. f=2:4). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15 season, Bicep3 will have survey speed comparable to Keck Array 150 GHz (2013), and will signifcantly enhance spectral separation of primordial B-mode power from that of possible galactic dust contamination in the Bicep2 observation patch.

Full-Polarization Modeling of Monostatic and Bistatic Radar Scattering From a Rough Sea Surface

Abstract: Fully polarimetric radars have advantages compared to more conventional single-polarization radars when measuring ocean wave characteristics. However, the theoretical analysis of full-polarization radar scattering frequently presents a challenge. For example, the classical composite model fails to correctly predict the cross-polarization components of the normalized radar cross section (NRCS). The new version of the numerical implementation of the small slope approximation of the second order, the SSA2, is presented in this paper. The SSA2 correctly predicts the behavior of out-of-plane bistatic scattering for an arbitrary set of polarization indices. The SSA2, as contrasted with the composite model, accounts for Bragg scattering of the second order which is essential for modeling cross-polarization scattering. We present the results of numerical simulations of both monostatic and bistatic cross sections and scattering amplitude correlators for various ocean conditions and transmitter-receiver geometries using the SSA2. We compare them with available experimental data and other modeling results.

Uniform Polarimetric Matrix Rotation Theory and Its Applications

Abstract: This paper presents the development of a uniform polarimetric matrix rotation theory in the rotation domain along the radar line of sight for polarimetric synthetic aperture radar (PolSAR) data interpretation The uniform representation of each coherency matrix element is a sinusoidal function in the rotation domain A set of oscillation parameters, including oscillation amplitude, oscillation center, angular frequency, and initial angle, is proposed to fully characterize the scattering behavior in the rotation domain A set of rotation angle parameters, including stationary angle, null angle, and minimization/maximization angles, is derived to indicate specific states of the rotation property The rotation relationships between the coherency and covariance matrices with linear and circular polarization bases are established A look-up table for these parameters is provided, and their physical meanings are interpreted These derived parameters directly link to the Huynen parameters Therefore, the proposed theory has the ability to achieve a desired state of one Huynen parameter by rotating the polarimetric matrix at a designated rotation angle This theory also generalizes both the classic polarization orientation angle originally derived from the covariance matrix in a circular polarization basis and the deorientation theory developed from the minimization of the cross-polarization term The roll-invariant terms have also been summarized Finally, multifrequency Pi-SAR and AIRSAR PolSAR data sets are used to demonstrate the derived parameters One oscillation amplitude parameter has been verified to be especially suitable for characterization of oriented man-made targets Two angle parameters are sensitive to the reflection symmetry condition and crop types Therefore, a simple unsupervised classification scheme has been developed and demonstrated Further utilization perspectives of the proposed theory have been discussed

Probing magnetar magnetosphere through X-ray polarization measurements

Abstract: The study of magnetars is of particular relevance since these objects are the only laboratories where the physics in ultra-strong magnetic fields can be directly tested. Until now, spectroscopic and timing measurements at X-ray energies in soft gamma-repeaters (SGRs) and anomalous X-ray pulsar (AXPs) have been the main source of information about the physical properties of a magnetar and of its magnetosphere. Spectral fitting in the ~ 0.5-10 keV range allowed to validate the "twisted magnetosphere" model, probing the structure of the external field and estimating the density and velocity of the magnetospheric currents. Spectroscopy alone, however, may fail in disambiguating the two key parameters governing magnetospheric scattering (the charge velocity and the twist angle) and is quite insensitive to the source geometry. X-ray polarimetry, on the other hand, can provide a quantum leap in the field by adding two extra observables, the linear polarization degree and the polarization angle. Using the bright AXP 1RXS J170849.0-400910 as a template, we show that phase-resolved polarimetric measurements can unambiguously determine the model parameters, even with a small X-ray polarimetry mission carrying modern photoelectric detectors and existing X-ray optics. We also show that polarimetric measurements can pinpoint vacuum polarization effects and thus provide an indirect evidence for ultra-strong magnetic fields.

Lupus I Observations from the 2010 Flight of the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry

Abstract: The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) was created by adding polarimetric capability to the BLAST experiment that was flown in 2003, 2005, and 2006. BLASTPol inherited BLAST's 1.8 m primary and its Herschel/SPIRE heritage focal plane that allows simultaneous observation at 250, 350, and 500 μm. We flew BLASTPol in 2010 and again in 2012. Both were long duration Antarctic flights. Here we present polarimetry of the nearby filamentary dark cloud Lupus I obtained during the 2010 flight. Despite limitations imposed by the effects of a damaged optical component, we were able to clearly detect submillimeter polarization on degree scales. We compare the resulting BLASTPol magnetic field map with a similar map made via optical polarimetry. (The optical data were published in 1998 by J. Rizzo and collaborators.) The two maps partially overlap and are reasonably consistent with one another. We compare these magnetic field maps to the orientations of filaments in Lupus I, and we find that the dominant filament in the cloud is approximately perpendicular to the large-scale field, while secondary filaments appear to run parallel to the magnetic fields in their vicinities. This is similar to what is observed in Serpens South via near-IR polarimetry, and consistent with what is seen in MHD simulations by F. Nakamura and Z. Li.

BICEP3: a 95 GHz refracting telescope for degree-scale CMB polarization

Abstract: BICEP3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz. It adopts the methodology of BICEP1, BICEP2 and the Keck Array experiments - it possesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, BICEP3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5$\times$ larger than a BICEP2/Keck Array receiver and faster optics ($f/1.6$ vs. $f/2.4$). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15 season, BICEP3 will have survey speed comparable to Keck Array 150 GHz (2013), and will significantly enhance spectral separation of primordial B-mode power from that of possible galactic dust contamination in the BICEP2 observation patch.

Polarimetric ghost imaging

Abstract: For conventional ghost imaging (GI) systems, the object image is obtained based on the reflective or transmissive character of the object. When the object and its background have the same reflectivity or transmittance, conventional GI is helpless in detecting the object from the background. An improvement is to use the polarization components of the reflected or transmitted light. We propose a polarimetric GI system that employs a polarization state generator and a polarization state analyzer. This feature allows for the first time, to the best of our knowledge, imaging the object buried in the same reflectivity or transmittance background, which represents a breakthrough for GI applications. Using a combination of intensity and polarization information, we are better able to distinguish between the background and the different material objects.

Nano-fabricated pixelated micropolarizer array for visible imaging polarimetry

Abstract: Pixelated micropolarizer array (PMA) is a novel concept for real-time visible imaging polarimetry A 320 × 240 aluminum PMA fabricated by electron beam lithography is described in this paper The period, duty ratio, and depth of the grating are 140 nm, 05, and 100 nm, respectively The units are standard square structures and the metal nanowires of the grating are collimating and uniformly thick The extinction ratio of 75 and the maximum polarization transmittance of 788% demonstrate that the PMA is suitable for polarization imaging When the PMA is applied to real-time polarization imaging, the degree of linear polarization image and the angle of linear polarization image are calculated from a single frame image The polarized target object is highlighted from the unpolarized background, and the surface contour of the target object can be reflected by the polarization angle

HONIR: an optical and near-infrared simultaneous imager, spectrograph, and polarimeter for the 1.5-m Kanata telescope

Abstract: We have developed an optical and near-infrared instrument HONIR (Hiroshima Optical and Near-InfraRed camera) with imaging, spectroscopy, and polarimetry capabilities in two (one optical and one near-infrared) bands simultaneously. Imaging capability with a field of view of 10 arcmin by 10 arcmin has been available since 2011, as reported in the previous SPIE conference. In addition, spectroscopic and polarimetric optical components (grisms, an Wollaston prism, a half-wave plate, and focal masks) were installed in the instrument, which enabled us to perform spectroscopy and linear polarization measurement by imaging polarimetry and spectro-polarimetry. Spectral resolution of R = λ/(triangle)λ ~ 440 - 800 is achieved in spectroscopy using a slit mask with an 1".3 width. In polarimetry, instrumental polarization is less than ~0.05 % with stability of better than ~0.05 %, which is sufficiently small to achieve an aimed accuracy of polarization measurement of ~0.1 % at primal observing wavelengths.

Polarization and polarimetry: a review

Abstract: Polarization is a basic property of light and is fundamentally linked to the internal geometry of a source of radiation. Polarimetry complements photometric, spectroscopic, and imaging analyses of sources of radiation and has made possible multiple astrophysical discoveries. In this article I review (i) the physical basics of polarization: electromagnetic waves, photons, and parameterizations; (ii) astrophysical sources of polarization: scattering, synchrotron radiation, active media, and the Zeeman, GoldreichKylafis, and Hanle effects, as well as interactions between polarization and matter (like birefringence, Faraday rotation, or the Chandrasekhar-Fermi effect); (iii) observational methodology: on-sky geometry, influence of atmosphere and instrumental polarization, polarization statistics, and observational techniques for radio, optical, and X/ wavelengths; and (iv) science cases for astronomical polarimetry: solar and stellar physics, planetary system bodies, interstellar matter, astrobiology, astronomical masers, pulsars, galactic magnetic fields, gamma-ray bursts, active galactic nuclei, and cosmic microwave background radiation.

High contrast polarimetry in the infrared with SPHERE on the VLT

Abstract: The instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), recently installed on the VLT-UT3, aims to detected and characterize giant extra-solar planets and the circumstellar environments in the very close vicinity of bright stars. The extreme brightness contrast and small angular separation between the planets or disks and their parent stars have so far proven very challenging. SPHERE will meet this challenge by using an extreme AO, stellar coronagraphs, an infrared dual band and polarimetric imager called IRDIS, an integral field spectrograph, and a visible polarimetric differential imager called ZIMPOL. Polarimetry allows a separation of the light coming from an unpolarized source such as a star and the polarized source such as a planet or protoplanetary disks. In this paper we present the performance of the infrared polarimetric imager based on experimental validations performed within SPHERE before the preliminary acceptance in Europe. We report on the level of instrumental polarization in the infrared and its calibration limit. Using differential polarimetry technique, we quantify the level of speckle suppression, and hence improved sensitivity in the context of imaging extended stellar environments.

Averaged Stokes polarimetry applied to evaluate retardance and flicker in PA-LCoS devices

Abstract: Recently we proposed a novel polarimetric method, based on Stokes polarimetry, enabling the characterization of the linear retardance and its flicker amplitude in electro-optic devices behaving as variable linear retarders. In this work we apply extensively the technique to parallel-aligned liquid crystal on silicon devices (PA-LCoS) under the most typical working conditions. As a previous step we provide some experimental analysis to delimitate the robustness of the technique dealing with its repeatability and its reproducibility. Then we analyze the dependencies of retardance and flicker for different digital sequence formats and for a wide variety of working geometries.

Polarization-modulated second harmonic generation ellipsometric microscopy at video rate.

Abstract: Fast 8 MHz polarization modulation coupled with analytical modeling, fast beam-scanning, and synchronous digitization (SD) have enabled simultaneous nonlinear optical Stokes ellipsometry (NOSE) and polarized laser transmittance imaging with image acquisition rates up to video rate. In contrast to polarimetry, in which the polarization state of the exiting beam is recorded, NOSE enables recovery of the complex-valued Jones tensor of the sample that describes all polarization-dependent observables of the measurement. Every video-rate scan produces a set of 30 images (10 for each detector with three detectors operating in parallel), each of which corresponds to a different polarization-dependent result. Linear fitting of this image set contracts it down to a set of five parameters for each detector in second harmonic generation (SHG) and three parameters for the transmittance of the incident beam. These parameters can in turn be used to recover the Jones tensor elements of the sample. Following validation of...

Empirical modelling of the BLASTPol achromatic half-wave plate for precision submillimetre polarimetry

Abstract: A cryogenic achromatic half-wave plate (HWP) for submillimetre astronomical polarimetry has been designed, manufactured, tested and deployed in the Balloon-borne Large-Aperture Submillimeter Telescope for Polarimetry (BLASTPol). The design is based on the five-slab Pancharatnam recipe and itworks in thewavelength range 200–600 μm, making it the broadestband HWP built to date at (sub)millimetre wavelengths. The frequency behaviour of the HWP has been fully characterized at room and cryogenic temperatures with incoherent radiation from a polarizing Fourier transform spectrometer. We develop a novel empirical model, complementary to the physical and analytical ones available in the literature, that allows us to recover the HWP Mueller matrix and phase shift as a function of frequency and extrapolated to 4 K. We show that most of the HWP non-idealities can be modelled by quantifying one wavelength-dependent parameter, the position of the HWP equivalent axes, which is then readily implemented in a map-making algorithm. We derive this parameter for a range of spectral signatures of input astronomical sources relevant to BLASTPol, and provide a benchmark example of how our method can yield improved accuracy on measurements of the polarization angle on the sky at submillimetre wavelengths.

Design and Performance of the X-ray Polarimeter X-Calibur

Abstract: X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems, micro-quasars, active galactic nuclei, neutron stars, and gamma-ray bursts. We designed, built and tested a X-ray polarimeter, X-Calibur, to be used in the focal plane of the balloon-borne InFOCμS grazing incidence X-ray telescope. X-Calibur combines a low-Z scatterer with a Cadmium Zinc Telluride (CZT) detector assembly to measure the polarization of 20–80 keV X-rays making use of the fact that polarized photons scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of ≃80%. The X-Calibur detector assembly is completed, tested, and fully calibrated. The response to a polarized X-ray beam was measured successfully at the Cornell High Energy Synchrotron Source. This paper describes the design, calibration and performance of the X-Calibur polarimeter. In principle, a similar space-borne scattering polarimeter could operate over the broader 2–100 keV energy band.

Visualization of the spatial–temporal evolution of continuous electromagnetic waves in the terahertz range based on photonics technology

Abstract: Visualization of the field evolution of the continuous waves in the terahertz (THz) range with high phase and spatial resolution is a new approach to the study of the physical dynamics of unique beams, such as nondiffractive, self-reconstructing, and vortex beams. As near-field visualization can reveal device dynamics, it is also useful for diagnosing the THz devices. Here, we demonstrate the visualization of the spatial–temporal evolution of freely propagating continuous THz waves by adapting the nonpolarimetric electro-optic (EO) detection technique to the self-heterodyne system. The amplitude and phase of a THz wave (125 GHz, λ=2.4 mm, 650 μW) radiated from a horn antenna were simultaneously and precisely measured in the self-heterodyne system, in which two frequency-detuned free-running lasers were used both for the generation (photomixing) and EO detection of THz waves. The nonpolarimetric EO detection technique has solved an intrinsic problem of the conventional polarimetric EO detection technique, in which the sensitivity of the measurements can be changed drastically by the fluctuation of the polarization state of the optical local oscillator signal for the EO detection. As a result, field evolution could be visualized with a maximum signal-to-noise ratio of 27 dB and a phase resolution of 2π/78 rad (80 mrad), by scanning an optical fiber-mounted EO crystal (ZnTe) in a free space repeatedly.

The imaging properties of the gas pixel detector as a focal plane polarimeter

Abstract: X-rays are particularly suited to probe the physics of extreme objects. However, despite the enormousimprovements of X-ray Astronomy in imaging, spectroscopy and timing, polarimetry remains largelyunexplored. We propose the photoelectric polarimeter Gas Pixel Detector (GPD) as an instrumentcandidate to fill the gap of more than thirty years of lack of measurements. The GPD, in the focusof a telescope, will increase the sensitivity of orders of magnitude. Moreover, since it can measurethe energy, the position, the arrival time and the polarization angle of every single photon, allows toperform polarimetry of subsets of data singled out from the spectrum, the light curve or the imageof source. The GPD has an intrinsic very fine imaging capability and in this work we report on thecalibrationcampaign carriedout in 2012at the PANTER X-raytest facility of the Max-Planck-Institutfu¨r extraterrestrische Physik of Garching (Germany) in which, for the first time, we coupled it to aJET-X optics module with a focal length of 3.5 m and an angular resolution of 18 arcsec at 4.5 keV.This configuration was proposed in 2012 aboard the X-ray Imaging Polarimetry Explorer (XIPE) inresponse to the ESA call for a small mission. We derived the imaging and polarimetric performancefor extended sources like Pulsar Wind Nebulae and Supernova Remnants as case studies for the XIPEconfiguration, discussing also possible improvements by coupling the detector with advanced optics,having finer angular resolution and larger effective area, to study with more details extended objects.Keywords: X-ray polarimetry, X-ray telescope, angular resolution

Multi-Chroic Dual-Polarization Bolometric Detectors for Studies of the Cosmic Microwave Background

Abstract: We are developing multi-chroic antenna-coupled Transition Edge Sensor (TES) bolometer detectors for Cosmic Microwave Background (CMB) polarimetry. Multi-chroic detectors increase focal plane area efficiency, and thus the mapping speed per focal plane area, and provide greater discrimination against polarized galactic foregrounds with no increase in weight or cryogenic cost. In each pixel, a silicon lens-coupled dual-polarized sinuous antenna collects photons over a two-octave frequency band. The antenna couples the broadband millimeter wave signal into microstrip transmission lines, and on-chip filter banks split the broadband signal into multiple frequency bands. Separate TES bolometers detect the power in each frequency band and linear polarization state. We will describe the design and performance of these devices and present optical data taken. Our measurements of dual-polarization pixels in multiple frequency bands show beams with percent-level ellipticity, and percent-level cross-polarization leakage. We will also describe the development of large arrays of these multi-chroic pixels. Finally, we will describe kilo-pixel arrays of these detectors planned for the future CMB experiments that will achieve unprecedented mapping speed.

Retardance and flicker modeling and characterization of electro-optic linear retarders by averaged Stokes polarimetry

Abstract: A polarimetric method for the measurement of linear retardance in the presence of phase fluctuations is presented. This can be applied to electro-optic devices behaving as variable linear retarders. The method is based on an extended Mueller matrix model for the linear retarder containing the time-averaged effects of the instabilities. As a result, an averaged Stokes polarimetry technique is proposed to characterize both the retardance and its flicker magnitude. Predictive capability of the approach is experimentally demonstrated, validating the model and the calibration technique. The approach is applied to liquid crystal on silicon displays (LCoS) using a commercial Stokes polarimeter. Both the magnitude of the average retardance and the amplitude of its fluctuation are obtained for each gray level value addressed, thus enabling a complete phase characterization of the LCoS.

Compressed sensing applied to weather radar

Abstract: We propose an innovative meteorological radar, which uses reduced number of spatiotemporal samples without compromising the accuracy of target information. Our approach extends recent research on compressed sensing (CS) for radar remote sensing of hard point scatterers to volumetric targets. The previously published CS-based radar techniques are not applicable for sampling weather since the precipitation echoes lack sparsity in both range-time and Doppler domains. We propose an alternative approach by adopting the latest advances in matrix completion algorithms to demonstrate the sparse sensing of weather echoes. We use Iowa X-band Polarimetric (XPOL) radar data to test and illustrate our algorithms.

Semi-automatic laboratory goniospectrometer system for performing multi-angular reflectance and polarization measurements for natural surfaces.

Abstract: In this paper, the design and operation of the Northeast Normal University Laboratory Goniospectrometer System for performing multi-angular reflected and polarized measurements under controlled illumination conditions is described. A semi-automatic arm, which is carried on a rotated circular ring, enables the acquisition of a large number of measurements of surface Bidirectional Reflectance Factor (BRF) over the full hemisphere. In addition, a set of polarizing optics enables the linear polarization over the spectrum from 350 nm to 2300 nm. Because of the stable measurement condition in the laboratory, the BRF and linear polarization has an average uncertainty of 1% and less than 5% depending on the sample property, respectively. The polarimetric accuracy of the instrument is below 0.01 in the form of the absolute value of degree of linear polarization, which is established by measuring a Spectralon plane. This paper also presents the reflectance and polarization of snow, soil, sand, and ice measured during 2010–2013 in order to illustrate its stability and accuracy. These measurement results are useful to understand the scattering property of natural surfaces on Earth.

Single-shot spatially modulated Stokes polarimeter based on a GRIN lens

Abstract: A new polarimeter for the simultaneous measurement of all Stokes parameters in a single shot is presented. It consists of only a gradient index (GRIN) lens, a polarizer, an imaging lens, and a CCD, without mechanical movements, electrical signal modulation, or the division of amplitude components. This design takes advantage of the continuous spatial distributions of birefringence value and the fast axis direction of a GRIN lens and derives the state of polarization (SOP) of the incident beam from the characteristic patterns on the CCD images. Tests show that this polarimeter is very accurate even with low-resolution images. It is versatile and adapts to light sources of different wavelengths. It is also very stable, robust, low cost, and simple to use.

Integration of Polarimetric PALSAR Attributes and Local Geomorphometric Variables Derived from SRTM for Forest Biomass Modeling in Central Amazonia

Abstract: . The objective of this work is to generate a predictive model for biomass estimation in a forested area of central Amazonia based on the integration of incoherent target scattering decomposition polarimetric attributes extracted from Phased Array type L-band Synthetic Aperture Radar (PALSAR) data and geomorphometric variables derived from Shuttle Radar Topography Mission (SRTM). In addition to their incorporation as variables of ecophysiological nature in biomass modeling, the geomorphometrics variables were also evaluated with regard to the possibility of minimization of topographic effects that affect the acquisition of PALSAR data. Based on the processed data, three biomass models were generated. The first model involves independent parameters extracted from polarimetric PALSAR data, the second includes the same polarimetric variables, which are additionally adjusted for the cosine factor effect. The third model integrates both the polarimetric parameters extracted from PALSAR and the geomorph...

Characterization of High Grazing Angle X-Band Sea-Clutter Doppler Spectra

Abstract: Collection of radar sea-clutter is typically performed from the top of a cliff looking out to sea, as it is relatively simple and inexpensive. This constrains the radar look direction with respect to the wind and limits the grazing angle. To improve our understanding at high grazing angles in the range 15° to 45°, the Defence Science and Technology Organisation's Ingara airborne X-band fully polarimetric radar has been used to collect 12 days worth of sea-clutter data. It has previously been shown that Walker's mean Doppler spectrum model is not suitable at these grazing angles; hence, a new two-component model is proposed that captures both the slow Bragg component and the fast non-Bragg component of the radar backscatter. A temporal decorrelation model is then presented that can be used to provide realistic performance prediction modeling.