Polarimetric Signatures Research Articles

Joint DOA and Polarization Estimation for Unequal Power Sources

For most joint direction of arrival (DOA) and polarization estimation methods, the performances of proposed methods in dealing with unequal power sources are not discussed. However, sources with unequal powers apparently exist widely in actual applications. In this study, we propose a joint DOA and polarization estimation method for unequal power sources by utilizing the invariance property of noise subspace (IPNS) to the power of sources. This work extends the IPNS method to the dual polarized antenna array for joint DOA and polarization estimation. Moreover, we theoretically prove that the IPNS remains valid even when the sources are correlated. The computer simulations illustrate that the proposed method can effectively estimate the DOA and polarization parameters as the power difference between sources increases, as opposed to the polarimetric multiple signal classification (MUSIC) algorithm, which suffers from degradation in resolution probability. In addition, the performances of the proposed method are provided, as well the Cramer Rao Bound (CRB), which show approximate performance as the polarimetric MUSIC algorithm.

Mass Flows in Massive Binaries: Clues from Spectropolarimetry

Because most massive stars have been or will be affected by a companion during the course of their evolution, we cannot afford to neglect binaries when discussing the progenitors of supernovae and GRBs. Analyzing linear polarization in the emission lines of close binary systems allows us to probe the structures of these systems' winds and mass flows, making it possible to map the complex morphologies of the mass loss and mass transfer structures that shape their subsequent evolution. In Wolf-Rayet (WR) binaries, line polarization variations with orbital phase distinguish polarimetric signatures arising from lines that scatter near the stars from those that scatter far from the orbital plane. These far-scattering lines may form the basis for a “binary line-effect method” of identifying rapidly rotating WR stars (and hence GRB progenitor candidates) in binary systems.

A Polarimetric and Microphysical Investigation of the Northeast Blizzard of 8–9 February 2013

Abstract On 8–9 February 2013, the northeastern United States experienced a historic winter weather event ranking among the top five worst blizzards in the region. Heavy snowfall and blizzard conditions occurred from northern New Jersey, inland to New York, and northward through Maine. Storm-total snow accumulations of 30–61 cm were common, with maximum accumulations up to 102 cm and snowfall rates exceeding 15 cm h−1. Dual-polarization radar measurements collected for this winter event provide valuable insights into storm microphysical processes. In this study, polarimetric data from the Weather Surveillance Radar-1988 Doppler (WSR-88D) in Upton, New York (KOKX), are investigated alongside thermodynamic analyses from the 13-km Rapid Refresh model and surface precipitation type observations from both Meteorological Phenomena Identification Near the Ground (mPING) and the National Weather Service (NWS) Forecast Office in Upton, New York, for interpretation of polarimetric signatures. The storm exhibited unique polarimetric signatures, some of which have never before been documented for a winter system. Reflectivity values were unusually large, reaching magnitudes >50 dBZ in shallow regions of heavy wet snow near the surface. The 0°C transition line was exceptionally distinct in the polarimetric imagery, providing detail that was often unmatched by the numerical model output. Other features include differential attenuation of magnitudes typical of melting hail, depolarization streaks that provide evidence of electrification, nonuniform beamfilling, a “snow flare” signature, and localized downward excursions of the melting-layer bright band collocated with observed transitions in surface precipitation types. In agreement with previous studies, widespread elevated depositional growth layers, located at temperatures near the model-predicted −15°C isotherm, appear to be correlated with increased snowfall and large reflectivity factors ZH near the surface.

Data-model comparison using FORWARD and CoMP

AbstractThe FORWARD SolarSoft IDL package is a community resource for model-data comparison, with a particular emphasis on analyzing coronal magnetic fields. FORWARD allows the synthesis of coronal polarimetric signals at visible, infrared, and radio frequencies, and will soon be augmented for ultraviolet polarimetry. In this paper we focus on observations of the infrared (IR) forbidden lines of Fe XIII, and describe how FORWARD may be used to directly access these data from the Mauna Loa Solar Observatory Coronal Multi-channel Polarimeter (MLSO/CoMP), to put them in the context of other space- and ground-based observations, and to compare them to synthetic observables generated from magnetohydrodynamic (MHD) models.

The importance of non-photon noise in astronomical spectropolarimetry

AbstractStellar spectropolarimetry has become an extremely popular technique during the last decade or two, and has led to major advances in the studies of stellar magnetic fields. Many important discoveries have been made thanks to ultra-precise measurements of very small polarimetric signals, which require very stable instruments and special observing strategies. The so called beam-swapping technique is a well-known polarimetric technique capable of suppressing many spurious signals due to various instrumental effects. However, when one is interested in ultra-high signal-to-noise ratio measurements, observers start to hit various limitations introduced by the instrument, by the atmosphere, and even by the software for data-reduction. These limitations cannot be overcome by the observing strategies, and sources of errors other than photon-noise must be taken into account. Here we discuss the advantages of the beam-swapping technique, and the impact of small instrument and atmospheric instabilities, and how these issues offer an explanation for the origin of the apparently significant observed polarisation signals produced by effects other than those intrinsic to the observed target.

Ground Clutter Mitigation for Weather Radars Using the Autocorrelation Spectral Density

Abstract Radar returns from the ground, known as ground clutter, can contaminate weather signals, often resulting in severely biased meteorological estimates. If not removed, these contaminants may artificially inflate quantitative precipitation estimates and obscure polarimetric and Doppler signatures of weather. A ground-clutter filter is typically employed to mitigate this contamination and provide less biased meteorological-variable estimates. This paper introduces a novel adaptive filter based on the autocorrelation spectral density, which is capable of mitigating the adverse effects of ground clutter without unnecessarily degrading the quality of the meteorological data. The so-called Clutter Environment Analysis using Adaptive Processing (CLEAN-AP) filter adjusts its suppression characteristics in real time to match dynamic atmospheric environments and meets Next Generation Weather Radar (NEXRAD) clutter-suppression requirements.

Characteristics Analysis and Classification of Crop Harvest Patterns by Exploiting High-Frequency MultiPolarization SAR Data

At harvest season, crops are often harvested using various methods at different times. Mapping and monitoring of the patterns of croplands during the harvest period provide information for farmers to help guide the harvest practices that are time critical and to support early warning of threats to food security. This study discusses the feasibility of high-frequency (C/X) polarimetric synthetic aperture radar (PolSAR) for the discrimination of crop patterns during harvest. The polarimetric signals gathered from a farmland area during harvest in Inner Mongolia, China, have been evaluated to investigate the properties of different harvest patterns by using the fully polarimetric Radarsat-2 and dual-pol TerraSAR-X images. A set of polarimetric parameters were derived from the datasets to interpret the radar signatures. The statistics show the sensitivity of the polarimetric parameters to the properties of the harvest patterns. The crop type, biomass, water content held by plants, crop swath direction, and crop state make a large contribution to the fluctuation of the polarimetric scattering characteristics. By exploring the polarimetric characteristics across different harvest patterns, a new method of mapping the harvest state is proposed by utilizing the decision tree algorithm. In the proposed method, GIS data are exploited to avoid the confusion of similar harvest patterns for different species. The harvest pattern mapping results by using the multipolarimetric data acquired over the study area in different years, demonstrate the feasibility and potential of polarimetric data of short wavelength for harvest pattern monitoring during harvest.

Polarimetric Contextual Classification of PolSAR Images Using Sparse Representation and Superpixels

In recent years, sparse representation-based techniques have shown great potential for pattern recognition problems. In this paper, the problem of polarimetric synthetic aperture radar (PolSAR) image classification is investigated using sparse representation-based classifiers (SRCs). We propose to take advantage of both polarimetric information and contextual information by combining sparsity-based classification methods with the concept of superpixels. Based on polarimetric feature vectors constructed by stacking a variety of polarimetric signatures and a superpixel map, two strategies are considered to perform polarimetric-contextual classification of PolSAR images. The first strategy starts by classifying the PolSAR image with pixel-wise SRC. Then, spatial regularization is imposed on the pixel-wise classification map by using majority voting within superpixels. In the second strategy, the PolSAR image is classified by taking superpixels as processing elements. The joint sparse representation-based classifier (JSRC) is employed to combine the polarimetric information contained in feature vectors and the contextual information provided by superpixels. Experimental results on real PolSAR datasets demonstrate the feasibility of the proposed approaches. It is proven that the classification performance is improved by using contextual information. A comparison with several other approaches also verifies the effectiveness of the proposed approach.

Some Considerations for the Use of High-Resolution Mobile Radar Data in Tornado Intensity Determination

Abstract The increasing number of mobile Doppler radars used in field campaigns across the central United States has led to an increasing number of high-resolution radar datasets of strong tornadoes. There are more than a few instances in which the radar-measured radial velocities substantially exceed the estimated wind speeds associated with the enhanced Fujita (EF) scale rating assigned to a particular tornado. It is imperative, however, to understand what the radar data represent if one wants to compare radar observations to damage-based EF-scale estimates. A violent tornado observed by the rapid-scan, X-band, polarimetric mobile radar (RaXPol) on 31 May 2013 contained radar-relative radial velocities exceeding 135 m s−1 in rural areas essentially devoid of structures from which damage ratings can be made. This case, along with others, serves as an excellent example of some of the complications that arise when comparing radar-estimated velocities with the criteria established in the EF scale. In addition, it is shown that data from polarimetric radars should reduce the variance of radar-relative radial velocity estimates within the debris field compared to data from single-polarization radars. Polarimetric radars can also be used to retrieve differential velocity, large magnitudes of which are spatially associated with large spectrum widths inside the polarimetric tornado debris signature in several datasets of intense tornadoes sampled by RaXPol.

Simulation and analysis of polarimetric radar signatures of human gaits

Radar observations of human activities have a variety of applications in security, defense, and rescue operations. Range-Doppler signatures of human motions are a useful tool for retrieving information on observed activities but require an understanding of the scattering processes involved to enable interpretation. This paper presents a study of human Doppler signatures using simulations, in particular focusing on the impact of the polarization to enable an understanding of any advantages in the use of polarimetric radar. The simulation model utilized is based on an approximate scattering approach combined with a 12-cylinder description of the human body. A comparison with single polarization co-pol measurements is used to show that the model provides reasonable first-order predictions of human signatures. Further simulations for polarimetric signatures illustrate the differing contributions of individual body parts to micro-Doppler returns and suggest that multi-polarization measurements can be useful in future micro-Doppler radar systems for human observation.

Signal analysis of a polarimetric fiber optic sensor for dynamic strain monitoring

Polarimetric fiber optic sensors have many advantages over other fiber optic sensors and strain gauges. As opposed to Fiber Bragg Grating sensors, polarimetric fiber sensors can be constructed with very simple, portable and robust experimental setup. In the paper we propose two methods of the polarimetric sensor output signal analyzing. First method is based on depolarization phenomena, and calculates degree of polarization (DOP), second one uses Fast Fourier Transform to analyze dynamic sensor response. Usefulness of both methods has been shown and experimentally proven. Full Text: PDF References K. Schroeder, W. Ecke, J. Apitz, E. Lembke, G. Lenschow, "A fibre Bragg grating sensor system monitors operational load in a wind turbine rotor blade," Meas. Sci. Technol. 17, 1167–1172 (2006). CrossRef G. Hegde, A. Asundi, "Performance analysis of all-fiber polarimetric strain sensor for composites structural health monitoring," NDT&E International 39, 320–327 (2006). CrossRef G. Wehrle, P. Nohama, H. J. Kalinowski, P. I. Torres, L. C. G.Valente, "A fibre optic Bragg grating strain sensor for monitoring ventilatory movements" Meas. Sci. Technol. 12, 805–809 (2001). CrossRef W. J. Bock, A. W. Domanski, T. R. Wolinski, "Influence of High Hydrostatic Pressure on Beat Length in Highly Birefringent Single-Mode Bow-Tie Fibers," Appl. Optics 29, 3484-3488 (1990). CrossRef A. W. Domański, M. Bieda, P. Lesiak, P. Makowski, M. Szeląg, T. Poczęsny, K. Prokopczuk, P. Sobotka, M. Chychłowski, M. Sierakowski, T. R. Woliński, "Polarimetric optical fiber sensors for dynamic strain measurement in composite materials," Acta Physica Polonica A. 124, 399-401 (2013). CrossRef P. Lesiak, G. Rajan, Y. Semenova, G. Farrell, A. Boczkowska, A. W. Domański, T. R. Woliński, "A hybrid highly birefringent fiber optic sensing system for simultaneous strain and temperature measurement," PLP 3, 140-142 (2010). CrossRef R. A. Chipman, "Depolarization in the Mueller Calculus," Proc. SPIE 5158, 184–192 (2003). CrossRef N. Furstenau, M. Schmidt, W. J. Bock, W. Urbanczyk, "Dynamic pressure sensing with a fiber-optic polarimetric pressure transducer with two-wavelength passive quadrature readout," App. Opt. 37, 663-671 (1998). CrossRef

SAR images analysis based on polarimetric signatures

In the presented paper a new method of identification of canonical coherent scatterers in the quad-polarimetric SAR data are presented. The proposed method is based on the analysis of polarimetric signatures. The observed signatures are compared with the polarimetric signatures of four canonical objects: trihedral, dihedral and helix – right and left which represent basic scattering mechanisms: single bounce, double bounce and helix scattering. The polarimetric matrices are treated as vectors in a unitary space with a scalar product that generates the norm. A recognized object is classified to one of the four coherent classes by a Kohonen network. It is not trained in an iteration process but its weights are adjusted according to the given patterns. The network classification is supported by rules. The obtained maps of pixels that represent canonical objects are compared with a map of coherent scatterers which was obtained by using the polarimetric entropy approach. The developed method of canonical coherent scatterers identification based on the polarimetric signatures analysis allows us not only to identify precisely the canonical coherent scatterers but also to determine the type of scattering mechanism characteristic for each of them. Since the proposed method works on a single-look (non-averaged) SAR data, it does not cause any spatial nor spectral decrease of amount of information because averaging is not conducted. Moreover, the proposed method will enable us the identification of a type of scattering mechanism in the canonical coherent pixels. This is an improvement in comparison to the existing methods. The obtained results should be more precise because the full polarimetric information about the scatterers is used in the identification procedure.

A Modified Polarimetric Synthetic Aperture Radar Classifier Using α/A/H Technique

Full polarimetric target recognition used in polarimetric synthetic aperture radar enables implementation of the recognition and classification of remote sensing images. This article investigates the classification of targets by target decomposition parameters, such as the scattering mechanism angle (α), anisotropy (A), and entropy (H), by using a new look-up table of region. The look-up table of region method is based on the combination of the H−A and A−α parameters. Because of the statistical properties of scatterers, the use of deterministic techniques, such as target decomposition, cannot be used. In these conditions, the look-up table of region is essentially required to evaluate the target parameters and classification of radar images. The goal of this study is the estimation of the polarimetric signatures, i.e., α/A/H, via a novel approach including the combination of target decomposition and look-up table of region. Data have been provided by the European Space Agency. Results show that the technique is excellent for target recognition and classification in statistical regions.

X-Band Polarimetric Observations of Cross Coupling in the Ice Phase of Convective Storms in Taiwan

AbstractIn this paper, experimental X-band polarimetric radar data from simultaneous transmission of horizontal (H) and vertical (V) polarizations (SHV) are shown, modeled, and microphysically interpreted. Both range–height indicator data and vertical-pointing X-band data from the Taiwan Experimental Atmospheric Mobile-Radar (TEAM-R) are presented. Some of the given X-band data are biased, which is very likely caused by cross coupling of the H and V transmitted waves as a result of aligned, canted ice crystals. Modeled SHV data are used to explain the observed polarimetric signatures. Coincident data from the National Center for Atmospheric Research S-band polarimetric radar (S-Pol) are presented to augment and support the X-band polarimetric observations and interpretations. The polarimetric S-Pol data are obtained via fast-alternating transmission of horizontal and vertical polarizations (FHV), and thus the S-band data are not contaminated by the cross coupling (except the linear depolarization ratio LDR) observed in the X-band data. The radar data reveal that there are regions in the ice phase where electric fields are apparently aligning ice crystals near vertically and thus causing negative specific differential phase Kdp. The vertical-pointing data also indicate the presence of preferentially aligned ice crystals that cause differential reflectivity Zdr and differential phase ϕdp to be strong functions of azimuth angle.

Linear Polarization and the Dynamics of Circumstellar Disks of Classical Be Stars

AbstractThe intrinsic linearly polarized light arising from electron scattering of stellar radiation in a non-spherically symmetric distribution of gas is a characterizing feature of classical Be stars. The distinct polarimetric signature provides a mean for directly probing the physical and geometric properties of the gaseous material enveloping these rapidly-rotating massive stars. Using a Monte Carlo radiative transfer computation and a self-consistent radiative equilibrium solution for the circumstellar gas, we explore the role of this observable signature in investigating the dynamical nature of classical Be star disks. In particular, we focus on the potential for using linearly polarized light to develop diagnostics of mass-loss events and to trace the evolution of the gas in a circumstellar disk. An informed context for interpreting the observed linear polarization signature can play an important role in identifying the physical process(es) which govern the formation and dissipation of the gaseous disks surrounding classical Be stars.

Early characteristics of the polarimetric tornadic debris signature associated with the 20 May 2013 Newcastle–Moore, Oklahoma, tornado

Early characteristics of the polarimetric tornadic debris signature associated with the 20 May 2013 Newcastle–Moore, Oklahoma, tornado

Light-scattering by aggregates of tumor cells: Spectral, polarimetric, and angular measurements

The goal of this paper is to present an in-vitro label-free technique based on light-scattering to study optical properties of MultiCellular Tumor Spheroids (MCTS). Our non-imaging technique provides a complete optical signature from hyperspectral polarimetric and angular light-scattering measurements using a coherent white-light supercontinuum laser-based instrument. We perform measurements on MCTS to demonstrate the feasibility of the technique. We report the spectral and angular-dependence of the depolarization of scattered-light by MCTS. This is the first time that the hyperspectral, polarimetric, and angular light-scattering signature of MCTS is reported. This work may provide new insight for the future development of the growth and proliferation of tumor cells.

Signal Design to Suppress Coupling in the Polarimetric Phased Array Radar

AbstractExamined are two related modes of polarimetric signal transmission that reduce coupling between the orthogonal components of received signals. For the surveillance scan with large unambiguous range and the simultaneous mode of horizontal (H) and vertical (V) transmission, pulse-to-pulse coding is suggested. It relaxes conditions on cross-coupling isolation from about 45 to about 25 dB while preserving the unambiguous range of over 460 km. For application to systematic codes during Doppler data acquisition, time-multiplexed (back to back) H and V pulses are proposed. This approach also relaxes the cross-coupling isolation to about 25 dB. These theoretically predicted values agree with those obtained by emulating the two schemes using oversampled time series data.

Reflectivity vortex hole in a tornadic supercell

The Weather Surveillance Radar-1988 Doppler (WSR-88D) at Thedford, Nebraska, detected a distinct reflectivity minimum in the hook echo of a tornadic supercell over north-central Nebraska on 11 August 2011. This “eye-like” feature was co-located with a tornadic vortex signature and was detectable to an altitude exceeding 8 km above ground level. A literature review of eye-like features in radar imagery in association with tornadic storms revealed that these signatures have been documented since the 1950s, but may have only recently become more commonly observed by WSR-88Ds with the change to super-resolution grid spacing. The reflectivity vortex hole observed on 11 August 2011 was analyzed using both constantelevation and three-dimensional radar imagery. Polarimetric radar data from WSR-88Ds in close proximity to four prominent tornadoes in May and June 2013 revealed at least brief reflectivity vortex holes with each of those cases, and suggested that recognition of vortex holes by meteorologists may supplement information from polarimetric tornadic debris signatures.

Identification of Coherent Scatterers in SAR Images Based on the Analysis of Polarimetric Signatures

In this letter, a new method of identification of coherent scatterers (CSs) in the quadpolarimetric synthetic aperture radar (SAR) data is introduced. The proposed method is based on the analysis of polarimetric signatures. The polarimetric signatures computed from real SAR data were compared with the polarimetric signatures of four canonical objects: trihedral, dihedral, left helix, and right helix. These canonical objects represent basic scattering mechanisms of single bounce, double bounce, and helix scattering. The obtained map of CSs was analyzed and compared with optical images of the studied region and with the map of polarized point scatterers obtained using the method proposed by S. R. Cloude. The developed method of the identification of CSs based on the polarimetric signature analysis gave promising results. It enables not only an accurate identification of the CSs but also a determination of the type of scattering mechanism that is characteristic for each of them.