Showing papers on "Polarimetry published in 2015"

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 (PSF) 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.

Efficient polarization beam splitter pixels based on a dielectric metasurface

Abstract: The polarization dependence of the reflection, refraction, and diffraction of electromagnetic waves from materials is measured in applications that extend from small (e.g., ellipsometry of semiconductor chips) to large scales (e.g., remote sensing for planetary science and weather radar). Such applications employ polarimeters that are in turn based on devices with polarization-selective absorption or reflection/refraction properties (e.g., prisms). The latter devices are generally bulky, thereby limiting their integration into compact systems. The former devices are inherently lossy, as they function by absorbing the unwanted polarization. Here, we experimentally demonstrate a conceptually novel method for pixel-level polarimetry. Each pixel contains amorphous-silicon nanoridges and deflects incident light in a polarization-dependent manner. As photons are sorted by polarization rather than filtered, the approach permits high efficiency. A high transmission efficiency of 90% and a high extinction ratio of 15 times are demonstrated.

The Extended Bragg Scattering Model-Based Method for Ship and Oil-Spill Observation Using Compact Polarimetric SAR

Abstract: Ocean surveillance is one of the important applications in synthetic aperture radar (SAR) imagery. Polarimetric SAR provides multichannel information and shows great potential for ocean target observation. Oil-spills and ships possess different polarimetric features from the ocean surface, whose physical backscattering property is generally admitted as being dominated by the Bragg resonant scattering. In this study, we focus on the oil-spill and ship observation based on the polarimetric features. Oil-spills present a non-Bragg scattering property. While backscatter from ships is predominated by the double-bounce scattering and the multiple reflections between the ship and sea surface. Ships exhibit very different scattering characteristics from the ocean Bragg scattering. Based on the extended Bragg (X-Bragg) model, a new method is proposed for observing oil-spills and ships. This method allows distinguishing oil-spills from two kinds of important look-alikes, i.e., biogenic slicks and the low-wind region (LWR), and also shows good performance for ship enhancement. Experiments are performed on the C-band fully polarimetric SAR data acquired by both SIR-C/X-SAR and RADARSAT-2. The other issue concerned is the application potential of the hybrid dual-polarimetric (i.e., compact polarimetry (CP)) SAR mode, which has the advantage of providing larger imaging coverage compared to the full polarimetry. Based on the X-Bragg model, where the backscatter reflection symmetry is assumed, an equivalent method is proposed with the circularly polarized transmission CP mode. Experimental results show that similar results can be obtained between the CP and full polarimetry for ocean target observation.

Angle-resolved cathodoluminescence imaging polarimetry

Abstract: Cathodoluminescence spectroscopy (CL) allows characterizing light emission in bulk and nanostructured materials and is a key tool in fields ranging from materials science to nanophotonics. Previously, CL measurements focused on the spectral content and angular distribution of emission, while the polarization was not fully determined. Here we demonstrate a technique to access the full polarization state of the cathodoluminescence emission, that is the Stokes parameters as a function of the emission angle. Using this technique, we measure the emission of metallic bullseye nanostructures and show that the handedness of the structure as well as nanoscale changes in excitation position induce large changes in polarization ellipticity and helicity. Furthermore, by exploiting the ability of polarimetry to distinguish polarized from unpolarized light, we quantify the contributions of different types of coherent and incoherent radiation to the emission of a gold surface, silicon and gallium arsenide bulk semiconductors. This technique paves the way for in-depth analysis of the emission mechanisms of nanostructured devices as well as macroscopic media.

K-space polarimetry of bullseye plasmon antennas

Abstract: Surface plasmon resonators can drastically redistribute incident light over different output wave vectors and polarizations. This can lead for instance to sub-diffraction sized nanoapertures in metal films that beam and to nanoparticle antennas that enable efficient conversion of photons between spatial modes, or helicity channels. We present a polarimetric Fourier microscope as a new experimental tool to completely characterize the angle-dependent polarization-resolved scattering of single nanostructures. Polarimetry allows determining the full Stokes parameters from just six Fourier images. The degree of polarization and the polarization ellipse are measured for each scattering direction collected by a high NA objective. We showcase the method on plasmonic bullseye antennas in a metal film, which are known to beam light efficiently. We find rich results for the polarization state of the beamed light, including complete conversion of input polarization from linear to circular and from one helicity to another. In addition to uncovering new physics for plasmonic groove antennas, the described technique projects to have a large impact in nanophotonics, in particular towards the investigation of a broad range of phenomena ranging from photon spin Hall effects, polarization to orbital angular momentum transfer and design of plasmon antennas.

Mass-Flux Characteristics of Tropical Cumulus Clouds from Wind Profiler Observations at Darwin, Australia

Abstract: Cumulus parameterizations in weather and climate models frequently apply mass-flux schemes in their description of tropical convection. Mass flux constitutes the product of the fractional area covered by convection in a model grid box and the vertical velocity in cumulus clouds. However, vertical velocities are difficult to observe on GCM scales, making the evaluation of mass-flux schemes difficult. Here, the authors combine high-temporal-resolution observations of in-cloud vertical velocities derived from a pair of wind profilers over two wet seasons at Darwin with physical properties of precipitating clouds [cloud-top heights (CTH), convective–stratiform classification] derived from the Darwin C-band polarimetric radar to provide estimates of cumulus mass flux and its constituents. The length of this dataset allows for investigations of the contributions from different cumulus cloud types—namely, congestus, deep, and overshooting convection—to the overall mass flux and of the influence of large-...

Hydrometeor classification from polarimetric radar measurements: a clustering approach

Abstract: . A data-driven approach to the classification of hydrometeors from measurements collected with polarimetric weather radars is proposed. In a first step, the optimal number of hydrometeor classes (nopt) that can be reliably identified from a large set of polarimetric data is determined. This is done by means of an unsupervised clustering technique guided by criteria related both to data similarity and to spatial smoothness of the classified images. In a second step, the nopt clusters are assigned to the appropriate hydrometeor class by means of human interpretation and comparisons with the output of other classification techniques. The main innovation in the proposed method is the unsupervised part: the hydrometeor classes are not defined a priori, but they are learned from data. The approach is applied to data collected by an X-band polarimetric weather radar during two field campaigns (from which about 50 precipitation events are used in the present study). Seven hydrometeor classes (nopt = 7) have been found in the data set, and they have been identified as light rain (LR), rain (RN), heavy rain (HR), melting snow (MS), ice crystals/small aggregates (CR), aggregates (AG), and rimed-ice particles (RI).

Demonstration of full 4×4 Mueller polarimetry through an optical fiber for endoscopic applications

Abstract: A novel technique to measure the full 4 × 4 Mueller matrix of a sample through an optical fiber is proposed, opening the way for endoscopic applications of Mueller polarimetry for biomedical diagnosis. The technique is based on two subsequent Mueller matrices measurements: one for characterizing the fiber only, and another for the assembly of fiber and sample. From this differential measurement, we proved theoretically that the polarimetric properties of the sample can be deduced. The proof of principle was experimentally validated by measuring various polarimetric parameters of known optical components. Images of manufactured and biological samples acquired by using this approach are also presented.

Change Detection in Full and Dual Polarization, Single- and Multifrequency SAR Data

Abstract: When the covariance matrix formulation is used for multilook polarimetric synthetic aperture radar (SAR) data, the complex Wishart distribution applies. Based on this distribution, a test statistic for equality of two complex variance–covariance matrices and an associated asymptotic probability of obtaining a smaller value of the test statistic are given. In a case study, airborne EMISAR C- and L-band SAR images from the spring of 1998 covering agricultural fields and wooded areas near Foulum, Denmark, are used in single- and bifrequency, bitemporal change detection with full and dual polarimetry data.

Error analysis of single-snapshot full-Stokes division-of-aperture imaging polarimeters.

Abstract: Single-snapshot full-Stokes imaging polarimetry is a powerful tool for the acquisition of the spatial polarization information in real time. According to the general linear model of a polarimeter, to recover full Stokes parameters at least four polarimetric intensities should be measured. In this paper, four types of single-snapshot full-Stokes division-of-aperture imaging polarimeter with four subapertures are presented and compared, with maximum spatial resolution for each polarimetric image on a single area-array detector. By using the error propagation theories for different incident states of polarization, the performance of four polarimeters are evaluated for several main sources of error, including retardance error, alignment error of retarders, and noise perturbation. The results show that the configuration of four 132° retarders with angular positions of ( ± 51.7°, ± 15.1°) is an optimal choice for the configuration of four subaperture single-snapshot full-Stokes imaging polarimeter. The tolerance and uncertainty of this configuration are analyzed.

Probing vacuum birefringence under a high-intensity laser field with gamma-ray polarimetry at the GeV scale

Abstract: Probing vacuum structures deformed by high intense fields is of great interest in general. In the context of quantum electrodynamics (QED), the vacuum exposed by a linearly polarized high-intensity laser field is expected to show birefringence. We consider the combination of a 10 PW laser system to pump the vacuum and 1 GeV photons to probe the birefringent effect. The vacuum birefringence can be measured via the polarization flip of the probe $\gamma$-rays which can also be interpreted as phase retardation of probe photons. We provide theoretically how to extract phase retardation of GeV probe photons via pair-wise topology of the Bethe-Heitler process in a polarimeter and then evaluate the measurability of the vacuum birefringence via phase retardation given a concrete polarimeter design with a realistic set of laser parameters and achievable pulse statistics.

Chiral cavity ring down polarimetry: Chirality and magnetometry measurements using signal reversals

Abstract: We present the theory and experimental details for chiral-cavity-ring-down polarimetry and magnetometry, based on ring cavities supporting counterpropagating laser beams. The optical-rotation symmetry is broken by the presence of both chiral and Faraday birefringence, giving rise to signal reversals which allow rapid background subtractions. We present the measurement of the specific rotation at 800 nm of vapors of α-pinene, 2-butanol, and α-phellandrene, the measurement of optical rotation of sucrose solutions in a flow cell, the measurement of the Verdet constant of fused silica, and measurements and theoretical treatment of evanescent-wave optical rotation at a prism surface. Therefore, these signal-enhancing and signal-reversing methods open the way for ultrasensitive polarimetry measurements in gases, liquids and solids, and at surfaces.

Simultaneous Linear and Circular Optical Polarimetry of Asteroid (4) Vesta

Abstract: From a single 3.8 hr observation of the asteroid (4) Vesta at 137 phase angle with the POlarimeter at Lick for Inclination Studies of Hot jupiters 2 (POLISH2) at the Lick Observatory Shane 3 m telescope, we confirm rotational modulation of linear polarization in the B and V bands. We measure the peak-to-peak modulation in the degree of linear polarization to be ΔP = (294 ± 35) × 10−6 (ppm) and time-averaged ΔP/P = 0.0575 ± 0.0069. After rotating the plane of linear polarization to the scattering plane, asteroidal rotational modulation is detected with 12σ confidence and observed solely in Stokes Q/I. POLISH2 simultaneously measures Stokes I, Q, U (linear polarization), and V (circular polarization), but we detect no significant circular polarization with a 1σ upper limit of 78 ppm in the B band. Circular polarization is expected to arise from multiple scattering of sunlight by rough surfaces, and it has previously been detected in nearly all other classes of solar system bodies except for asteroids. Subsequent observations may be compared with surface albedo maps from the Dawn Mission, which may allow the identification of compositional variation across the asteroidal surface. These results demonstrate the high accuracy achieved by POLISH2 at the Lick 3 m telescope, which is designed to directly detect scattered light from spatially unresolvable exoplanets.

Principles and Applications of Polarimetric SAR Tomography for the Characterization of Complex Environments

Abstract: Despite its widely recognized capabilities for mapping and characterizing large areas, 2-D Synthetic Aperture Radar (SAR) imaging meets serious limitations over volumetric media, due to its incapacity to discriminate scattering contributions in the elevation direction. This paper proposes some methods for characterizing complex volumetric environments using polarimetric SAR tomography, a 3-D imaging technique based on the use of diversely polarized electromagnetic waves acquired from different trajectories. The use of polarimetric diversity permits to both improve the tomographic separation between different components of complex volumetric media and to characterize the EM behavior of the observed environments. A set of spectral estimation techniques, adapted to tomographic focusing, are tested against signal models accounting for the statistical complexity of hybrid volumetric environments. Due to their statistical adaptivity, their robustness to mismodeling and their accuracy, spectral estimators based on weighted subspace fitting criteria are selected and extended to the polarimetric case. The effectiveness of the proposed approaches is assessed over real data and for three different applications, related to urban area 3-D mapping using a minimal set of images, tropical forest structure characterization using low frequency waves, and under-foliage concealed vehicle imaging.

Change Detection with Compact Polarimetric SAR for Monitoring Wetlands

Abstract: . Compact polarimetric synthetic aperture radar (SAR) architecture is an SAR configuration that consists of transmitting a single circular polarization (left or right) or a 45° oriented linear signal while receiving two linear polarizations, horizontal and vertical. In this study we investigate the potential of the compact polarimetric SAR mode for wetland monitoring applications. Whitewater Lake located in Manitoba, Canada, is selected as a case study where simulated compact polarimetric SAR data are obtained using RADARSAT-2 Fine Quad-POL SAR images. The ability of the compact polarimetric data to monitor wetlands using the Wishart-Chernoff distance is studied and compared to the results obtained using fully polarimetric data. Results of this study show that compact polarimetry provides monitoring capabilities for wetlands. Promising change detection mapping results based on the compact polarimetric coherency matrices are obtained using the Wishart-Chernoff distance. This could be useful for fla...

Invited Article: A novel calibration method for the JET real-time far infrared polarimeter and integration of polarimetry-based line-integrated density measurements for machine protection of a fusion plant.

Abstract: In this paper, we present the work in the implementation of a new calibration for the JET real-time polarimeter based on the complex amplitude ratio technique and a new self-validation mechanism of data. This allowed easy integration of the polarimetry measurements into the JET plasma density control (gas feedback control) and as well as machine protection systems (neutral beam injection heating safety interlocks). The new addition was used successfully during 2014 JET Campaign and is envisaged that will operate routinely from 2015 campaign onwards in any plasma condition (including ITER relevant scenarios). This mode of operation elevated the importance of the polarimetry as a diagnostic tool in the view of future fusion experiments.

A unified framework for crop classification in southern China using fully polarimetric, dual polarimetric, and compact polarimetric SAR data

Abstract: With the development of synthetic aperture radar SAR techniques, various imaging modes that involve single polarimetry, dual polarimetry, full polarimetry FP, and compact polarimetry CP have been proposed and applied to SAR systems. This article attempts to introduce a unified framework for crop classification in southern China using FP, coherent HH/VV, and CP data. By analysing the polarimetric response from different land-cover types including rice, banana trees, sugarcane, eucalyptus, water, and built-up areas in the experimental site and by exploring the similarities between data in these three modes, a knowledge-based characteristic space is created and a unified classification framework is presented. Time-series data acquired by TerraSAR-X over the Leizhou Peninsula, southern China, are used in our experiments. The overall classification accuracies for data in the FP and coherent HH/VV modes are approximately 95%, and for data in the CP mode, the accuracy is 91%, which suggest that the proposed classification scheme is effective. Compared with the Wishart Maximum Likelihood ML classifier, the proposed method provides approximately 5.64%, 7.30%, and 6.48% higher classification accuracies in the FP, HH/VV, and circular transmit and dual circular receive modes, respectively.

Weather radar polarimetry

Abstract: Dual-polarization radar promises to improve the modeling of convective storms. Dual-polarization radar promises to improve the modeling of convective storms.

Optimization, tolerance analysis and implementation of a Stokes polarimeter based on the conical refraction phenomenon.

Abstract: Recently, we introduced the basic concepts behind a new polarimeter device based on conical refraction (CR), which presents several appealing features compared to standard polarimeters. To name some of them, CR polarimeters retrieve the polarization state of an input light beam with a snapshot measurement, allow for substantially enhancing the data redundancy without increasing the measuring time, and avoid instrumental errors owing to rotating elements or phase-to-voltage calibration typical from dynamic devices. In this article, we present a comprehensive study of the optimization, robustness and parameters tolerance of CR based polarimeters. In addition, a particular CR based polarimetric architecture is experimentally implemented, and some concerns and recommendations are provided. Finally, the implemented polarimeter is experimentally tested by measuring different states of polarization, including fully and partially polarized light.

Linear polarization optimized Stokes polarimeter based on four-quadrant detector

Abstract: A four-quadrant detector (4QD) consists of four well-balanced detectors. We report on a Stokes polarimeter with optimal linear polarization measurements based on a 4QD. We turned the four intensity-detection channels into four polarization-analyzing channels by placing four polarizers and one quarter-wave plate in front of the individual detectors. An optimization method for the four polarization-analyzing channels is proposed to improve measurement accuracy. Considering applications in favor of linear polarization measurements instead of global optimization for all the possible states of polarization (SOP), we optimize the polarimeter first for the linear polarization components and then for the circular polarization component. The polarimeter is capable of simultaneous measurements of fast varying SOP with improved performance for the linear polarizations.

Model-Based Pseudo-Quad-Pol Reconstruction from Compact Polarimetry and Its Application to Oil-Spill Observation

Abstract: Compact polarimetry is an effective imaging mode for wide area observation, especially for the open ocean. In this study, we propose a new method for pseudo-quad-polarization reconstruction from compact polarimetry based on the three-component decomposition. By using the decomposed powers, the reconstruction model is established as a power-weighted model. Further, the phase of the copolarized correlation is taken into consideration. The phase of double-bounce scattering is closer to π than to 0, while the phase of surface scattering is closer to 0 than to π. By considering the negative (double-bounce reflection) and positive (surface reflection) copolarized correlation, the reconstruction model for full polarimetry has a good consistency with the real polarimetric SAR data. -band ALOS/PALSAR-1 fully polarimetric data acquired on August 27, 2006, over an oil-spill area are used for demonstration. Reconstruction performance is evaluated with a set of typical polarimetric oil-spill indicators. Quantitative comparison is given. Results show that the proposed model-based method is of great potential for oil-spill observation.

The modern aerosol retrieval algorithms based on the simultaneous measurements of the intensity and polarization of reflected solar light: a review

Abstract: In this paper the algorithms to retrieve atmospheric aerosol properties using spaceborne observations are reviewed The main focus is on the algorithms based on simultaneous measurements of the intensity and degree of polarization of reflected solar light at the top-of-atmosphere

Influence of Beam Broadening on the Accuracy of Radar Polarimetric Rainfall Estimation

Abstract: The quantitative estimation of rain rates using meteorological radar has been a major theme in radar meteorology and radar hydrology. The increase of interest in polarimetric radar is in part because polarization diversity can reduce the effect on radar precipitation estimates caused by raindrop size variability, which has allowed progress on radar rainfall estimation and on hydrometeorological applications. From an operational point of view, the promises regarding the improvement of radar rainfall accuracy have not yet been completely proven. The main reason behind these limits is the geometry of radar measurements combined with the variability of the spatial structure of the precipitation systems. To overcome these difficulties, a methodology has been developed to transform the estimated drop size distribution (DSD) provided by a vertically pointing micro rain radar to a profile given by a ground-based polarimetric radar. As a result, the rainfall rate at the ground is fixed at all ranges, where...

Spectral characterization of fine-scale wind waves using shipboard optical polarimetry

Abstract: Fine-scale sea surface waves are of profound importance to a number of air-sea interaction processes. Due to a number of reasons, there exists a great degree of difficulty in obtaining quality in situ observations of these waves. This paper presents the application of a shipboard wave-sensing method toward the following quantifications: regime-specific contribution to sea surface slope and sensitivity to wind speed increases. Measurements were made via polarimetric camera, resolving waves with wavelengths ranging from 0.21 to 0.003 m (30 rad/m < k < 1750 rad/m). The gravity-capillary regime was found to contribute the bulk of mean square slope during stationary wind conditions and supply the majority of mean square slope growth during periods of increasing wind speed. Capillary waves were found to contribute approximately 5% of the overall surface roughness. Furthermore, capillary waves were found to be the least sensitive to increases in wind speed. This implies that such waves saturate at low wind speeds ( ≈ 3 m/s) and slow wind speed increases ( ≈ 0.02 m/s2). The slight roughness contribution from capillary waves and significant contribution from gravity-capillary waves offers insight for scientists in the remote sensing field and important information for the formation of new wave models.

Self-Calibrating Imaging Polarimetry

Abstract: To map the polarization state (Stokes vector) of objects in a scene, images are typically acquired using a polarization filter (analyzer), set at different orientations Usually these orientations are assumed to be all known Often, however, the angles are unknown: most photographers manually rotate the filter in coarse undocumented angles Deviations in motorized stages or remote-sensing equipment are caused by device drift and environmental changes This work keeps the simplicity of uncontrolled uncalibrated photography, and still extracts from the photographs accurate polarimetry This is achieved despite unknown analyzer angles and the objects' Stokes vectors The paper derives modest conditions on the data size, to make this task well-posed and even over-constrained The paper then proposes an estimation algorithm, and tests it in real experiments The algorithm demonstrates high accuracy, speed, simplicity and robustness to strong noise and other signal disruptions

Flexible real-time MIMO channel sounder for multidimensional polarimetric parameter estimation

Abstract: This paper describes the architecture of a fully parallel multiple-input multiple-output (MIMO) channel sounder. It has been designed to give in real-time the full polarimetric channel matrix which is then exploited to display, for example, the bi-directional channel characteristics as the angle of arrival (AoA) and angle of departure (AoD) of the multipath components. This 16×16 sounder, working at a center frequency of 1.35 GHz, uses an OFDM transmission scheme with an 80 MHz bandwidth. Applications of this sounder are then illustrated by studying the outdoor to indoor propagation characteristics.

100 kHz Mueller polarimeter in reflection configuration.

Abstract: A new setup is proposed to perform high-speed Mueller polarimetry by spectral coding of polarization in a reflection configuration. The system uses a swept laser source and a photodiode, which results in a simple optical setup that allows measurement of Mueller matrices at 100 kHz repetition rate. A special focus is made on the influence of the cube beam splitter polarimetric response, which is essential to measurements in a reflection configuration. The instrument is first validated on reference samples for single-point measurements, and the effect of a proper system calibration is also demonstrated on polarimetric images. The device is intended to be implemented within a laser scanning microscope to perform multimodal imaging (confocal/multiphoton and Mueller polarimetry).

Measurement of polarization assemblies for the Daniel K. Inouye Solar Telescope

Abstract: We present here methodology and instrumentation for the precise measurement of retardance and optic axis orientation of retarder assemblies for the Daniel K. Inouye Solar Telescope. This solar telescope will perform broadband polarimetry of the sun. Each Meadowlark assembly is made up of three compound zero order retarders that must have a retardance variation of less than 6.33 nanometers across the greater than 110 millimeter clear aperture. The retardation of each component was measured using a combination of spectral transmission scans and ellipsometry, with test wavelengths of less than a 0.45 nanometer bandwidths and yielding a standard deviation in measurements of less than 0.001 waves. A technique for the measurement of the near zero window (Infrasil® and CaF 2 ) retardance is shown, in addition to retardance measurements of the component waveplates. An average retardance of 0.63 nm for CaF 2 and 0.28 nm for Infrasil® was found. Finally, a technique for determining the optic axis tilt of each crystal waveplate using laser ellipsometry is discussed.