Polarimetric Signatures Research Articles

Analysis of dual polarization images of precipitating clouds collected by the COSMO SkyMed constellation

Currently, several satellite missions are employing X-band synthetic aperture radars (SAR) with polarimetric capabilities. In images collected over land by X-band SAR, precipitation results mainly in evident attenuation of the surface returns. Effects of precipitation in polarimetric SAR images and how to exploit them for precipitation studies are emerging topics of interest. This paper investigates polarimetric signatures of precipitation in images collected by the X-band SARs of the Italian Space Agency COSMO SkyMed constellation using the HH-VV alternate polarimetric mode. Analyzed images were collected in 2010 when the constellation was composed of three satellites and operated in the “tandem like” interferometric configuration, which allowed acquisition of the same scene with the same viewing geometry and a minimum decorrelation time of one day. Observations collected in Piedmont (Italy) and Tampa Bay (Florida, US) have been analyzed along with coincident observations collected by operational weather radars, used to reconstruct the component of SAR returns due to precipitation at horizontal and vertical polarization states. Different techniques are used depending on the different characteristics of terrestrial radars. SAR observations reconstructed from terrestrial measurements are in fairly good agreement with actual SAR observations. Results confirm that the attenuation signature in SAR images collected over land is particularly pronounced in the presence of precipitation cells and can be related to the radar reflectivity integrated along the same path. The difference between copolar HH and VV power measurements reveals a differential attenuation due to anisotropy of precipitation, whose range is limited when the SAR incidence angle is low. A specific feature observed in the CosmoSkyMed alternate polarization implementation is the presence of the scalloping effect, a periodic effect along the azimuth direction that cannot always be removed by standard de-scalloping techniques. Amplitude of scalloping between the two polarizations can reach a couple of decibels, close to the maximum range of differential path integrated attenuation.

A Data-Adaptive Compressed Sensing Approach to Polarimetric SAR Tomography of Forested Areas

Super-resolution imaging via compressed sensing (CS)-based spectral estimators has been recently introduced to synthetic aperture radar (SAR) tomography. In the case of partial scatterers, the mainstream has so far been twofold, in that the tomographic reconstruction is conducted by either directly working with multiple looks and/or polarimetric channels or by exploiting the corresponding single-channel second-order statistics. In this letter, we unify these two methodologies in the context of covariance fitting. In essence, we exploit the fact that both vertical structures and the unknown polarimetric signatures can be approximated in a low-dimensional subspace. For this purpose, we make use of a wavelet basis in order to sparsely represent vertical structures. Additionally, we synthesize a data-adaptive orthonormal basis that spans the space of polarimetric signatures. Finally, we validate this approach by using fully polarimetric L-band data acquired by the E-SAR sensor of the German Aerospace Center (DLR).

Magnetic Field Diagnostics and Spatio-Temporal Variability of the Solar Transition Region

Magnetic field diagnostics of the transition region from the chromosphere to the corona faces us with the problem that one has to apply extreme UV spectro-polarimetry. While for coronal diagnostic techniques already exist through infrared coronagraphy above the limb and radio observations on the disk, for the transition region one has to investigate extreme UV observations. However, so far the success of such observations has been limited, but there are various projects to get spectro-polarimetric data in the extreme UV in the near future. Therefore it is timely to study the polarimetric signals we can expect for such observations through realistic forward modeling. We employ a 3D MHD forward model of the solar corona and synthesize the Stokes I and Stokes V profiles of C IV 1548 A. A signal well above 0.001 in Stokes V can be expected, even when integrating for several minutes in order to reach the required signal-to-noise ratio, despite the fact that the intensity in the model is rapidly changing (just as in observations). Often this variability of the intensity is used as an argument against transition region magnetic diagnostics which requires exposure times of minutes. However, the magnetic field is evolving much slower than the intensity, and thus when integrating in time the degree of (circular) polarization remains rather constant. Our study shows the feasibility to measure the transition region magnetic field, if a polarimetric accuracy on the order of 0.001 can be reached, which we can expect from planned instrumentation.

60 GHz Ultrawideband Polarimetric MIMO Sensing for Wireless Multi-Gigabit and Radar

Polarimetric radio wave processing becomes of increasing interest for very high-data rate wireless transmission and for short-range radar at millimeter-waves (mm-W). This goes along with the huge bandwidth of 7 to 9 GHz, which is available worldwide in the 60 GHz unlicensed band. In this paper, we propose a 60 GHz ultra-wideband (UWB) polarimetric multiple-input-multiple-output (MIMO) sensing system architecture and polarimetric signal processing for short-range communications and radar. Demonstration measurements were made by using an UWB radar interface. By measurements in multipath rich environments it is demonstrated that tap-wise polarimetric filtering in delay domain can enhance the 60 GHz link budget by filtering some paths and then reducing shadowing due to human activity. Additionally, optimum MIMO polarimetric filtering is proposed to reduce heavy clutter for mm-W radar, increasing by about 30 dB the signal-to-clutter-plus-noise-ratio.

Polarimetric Signatures above the Melting Layer in Winter Storms: An Observational and Modeling Study

AbstractPolarimetric radar observations above the melting layer in winter storms reveal enhanced differential reflectivity ZDR and specific differential phase shift KDP, collocated with reduced copolar correlation coefficient ρhv; these signatures often appear as isolated “pockets.” High-resolution RHIs and vertical profiles of polarimetric variables were analyzed for a winter storm that occurred in Oklahoma on 27 January 2009, observed with the polarimetric Weather Surveillance Radar-1988 Doppler (WSR-88D) in Norman. The ZDR maximum and ρhv minimum are located within the temperature range between −10° and −15°C, whereas the KDP maximum is located just below the ZDR maximum. These signatures are coincident with reflectivity factor ZH that increases toward the ground. A simple kinematical, one-dimensional, two-moment bulk microphysical model is developed and coupled with electromagnetic scattering calculations to explain the nature of the observed polarimetric signature. The microphysics model includes nucleation, deposition, and aggregation and considers only ice-phase hydrometeors. Vertical profiles of the polarimetric radar variables (ZH, ZDR, KDP, and ρhv) were calculated using the output from the microphysical model. The base model run reproduces the general profile and magnitude of the observed ZH and ρhv and the correct shape (but not magnitude) of ZDR and KDP. Several sensitivity experiments were conducted to determine if the modeled signatures of all variables can match the observed ones. The model was incapable of matching both the observed magnitude and shape of all polarimetric variables, however. This implies that some processes not included in the model (such as secondary ice generation) are important in producing the signature.

Observations of Polarimetric Signatures in Supercells by an X-Band Mobile Doppler Radar

Abstract Polarimetric weather radars significantly enhance the capability to infer the properties of scatterers within a resolution volume. Previous studies have identified several consistently seen polarimetric signatures in supercells observed in the central United States. Nearly all of these studies used data collected by fixed-site S- and C-band radars. Because there are few polarimetric mobile radars, relatively little has been documented in high-resolution polarimetric data from mobile radars. Compared to S and C bands, there has been very limited examination of polarimetric signatures at X band. The primary focus of this paper is on one signature that has not been documented previously and one that has had little documentation at X band. The first signature, seen in at least seven supercell datasets collected by a mobile, X-band, polarimetric radar, consists of a narrow band of locally reduced reflectivity factor ZH and differential reflectivity, typically near the location where the hook echo “attaches” to the main body of the storm echo. No consistent pattern is seen in radial velocity VR or copolar cross correlation ρHV. The small size of this feature suggests a significant heterogeneity in precipitation microphysics, the cause and impact of which are unknown. The greater resolution and the scattering differences at X band compared to other frequencies may make this feature more apparent. The second signature consists of anomalously low ρHV in areas of high ZH along the left section (relative to storm motion) of the bounded weak-echo region. Examples of other polarimetric signatures at X band are provided.

Low-Level Polarimetric Radar Signatures in EnKF Analyses and Forecasts of the May 8, 2003 Oklahoma City Tornadic Supercell: Impact of Multimoment Microphysics and Comparisons with Observation

The impact of increasing the number of predicted moments in a multimoment bulk microphysics scheme is investigated using ensemble Kalman filter analyses and forecasts of the May 8, 2003 Oklahoma City tornadic supercell storm and the analyses are validated using dual-polarization radar observations. The triple-moment version of the microphysics scheme exhibits the best performance, relative to the single- and double-moment versions, in reproducing the low-ZDRhail core and high-ZDRarc, as well as an improved probabilistic track forecast of the mesocyclone. A comparison of the impact of the improved microphysical scheme on probabilistic forecasts of the mesocyclone track with the observed tornado track is also discussed.

Polarimetric observations of the innermost regions of relativistic jets in X-ray binaries

Synchrotron emission from the relativistic jets launched close to black holes and neutron stars can be highly linearly polarized, depending on the configuration of the magnetic field. In X-ray binaries, optically thin synchrotron emission from the compact jets resides at infrared–optical wavelengths. The polarimetric signature of the jets is detected in the infrared and is highly variable in some X-ray binaries. This reveals the magnetic geometry in the compact jet, in a region close enough to the black hole that it is influenced by its strong gravity. In some cases the magnetic field is turbulent and variable near the jet base. In Cyg X–1, the origin of the γ -ray, X-ray and some of the infrared polarization is likely the optically thin synchrotron power law from the inner regions of the jet. In order to reproduce the polarization properties, the magnetic field in this region must be highly ordered, in contrast to other sources.

An Analysis of Vortices Embedded within a Quasi-Linear Convective System Using X-Band Polarimetric Radar

Abstract On 2 April 2010, a developing quasi-linear convective system (QLCS) moved rapidly northeastward through central Oklahoma spawning at least three intense, mesoscale vortices. At least two of these vortices caused damage rated as category 0 to 1 on the enhanced Fujita scale (EF0–EF1) in and near the town of Rush Springs. Two radar networks—the National Weather Service Weather Surveillance Radar-1988 Doppler network (WSR-88D) and the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) radar network—collected high spatial and temporal resolution data of the event. This study is an in-depth polarimetric analysis of mesovortices within a QLCS. In this case study, the storm development and evolution of the QLCS mesovortices are examined. Significant findings include the following: 1) The damage in Rush Springs was caused by a combination of the fast translation speed and the embedded circulations associated with QLCS vortices. The vortices’ relative winds nearly negated the storm motion to the left of the vortex, but doubled the ground-relative wind to the right of the vortex. 2) A significant differential reflectivity (ZDR) arc developed along the forward flank of the first vortex. The ZDR arc propagated northeastward along the QLCS with the development of each new vortex. 3) A minimum in the copolar correlation coefficient (ρhv) in the center of the strongest vortex was observed, indicating the likely existence of a polarimetric tornado debris signature (TDS). A secondary ρhv minimum also was found just to the right of the vortex center, possibly associated with lofted debris from straight-line winds.

Программное средство для моделирования, анализа и обработки сигналов развертывающих поляриметров

Программное средство для моделирования, анализа и обработки сигналов развертывающих поляриметров

Assessment of Scattering Mechanism of Polarimetric SAR Signal From Mountainous Forest Areas

This study aims to understand the effects of the topographic slope variation on the vegetation backscattering characteristics of polarimetric imaging radar. Most of the previous studies in modeling microwave backscattering signatures of vegetated area have been carried out over relatively flat areas. In order to model vegetation scattering mechanisms of mountainous forests, this paper presents an improvement of the radiative transfer model that accounts for the tilted scattering surface beneath a forest canopy. An L-band polarimetric synthetic aperture radar (SAR) data set acquired by the NASA/Jet Propulsion Laboratory Airborne SAR system was used to test and to assess the vegetation scattering model for a sloping forest area. Experimental result shows the proposed model to be adequate for evaluating slope-induced changes in microwave scattering mechanisms.

TERRAIN CORRECTION OF POLARIMETRIC SAR DATA AND ITS APPLICATION IN MAPPING MOUNTAIN GLACIER FACIES WITH RADARSAT-2 SAR

Abstract. Synthetic Aperture Radar (SAR) data can be difficult to interpret over glacierized terrain, especially in areas of high relief where most of the smaller glaciers of the world are found. The two primary objectives of this paper are to correct the topographically induce distortions inherent in SAR image of rugged terrain and to map glacier facies in the corrected polarimetric (PolSAR) image. Methods for terrain correction of PolSAR developed in this paper, which base on the coherency matrix data, utilize polarimetric signature to refine the location accuracy and perform the pixel size normalization on each element of the coherency matrix using the backward integration method. Moreover, azimuth-slope correction is immediately following after radiometric correction. A supervised classification is performed on the orthorectified image to map the spatial distribution of snow and ice. The visual boundary between wet snow and bare ice surface is delineated on the orthorectified image too. These results show that glacier facies and the wet snow line can be mapped reasonably well using Radarsat-2 PolSAR in a mountainous environment.

SAR POLARIMETRIC SIGNATURES FOR URBAN TARGETS – POLARIMETRIC SIGNATURE CALCULATION AND VISUALIZATION

Abstract. Various urban targets (land use) from Ahmedabad city were chosen, followed by generation of polarimetric signatures for each target using the developed tool. These polarimetric signatures were then studied and analyzed in detail. An attempt has been to develop a Polarimetric Signature Calculation and Visual Representation Tool assigned name "POLSIC", to generate Co-polarized and Cross polarized signatures, based on the calculation of Stokes Matrix and the backscattered power at various ellipticity and orientation angles. The input parameters required for the developed tool, are the amplitude and phase values of all the four polarizations, for each target using any quadpol radar imagery. In this study, RADARSAT-2 imagery has been used to obtain the amplitude and phase values of each target, in all four polarization states. Polarimetric signatures were generated for various urban targets using the developed tool. Vegetated land, built up in the city, built up within lake, and road were found to have an overall higher polarimetric response (backscattered power) as compared to grass lawn, fallow land and minimum in case of water body. Such Polarimetric responses were obtained due to factors like surface roughness and orientation of the target with respect to the radar look angle. The shape of the signature also indicates the scattering characteristics.

Resonance Based Target Recognition Using Ultrawideband Polarimetric Signatures

Automated target recognition based on resonances embedded in the ultrawideband transient signatures has been of significant research interest throughout the years. In most studies, targets are usually illuminated and measured using a linear polarized basis. This could lead to an incorrect result for target recognition as some resonant modes may not be well excited at that particular incident aspect and polarization state. In this communication, the possibility of using a full-polarimetric ultrawideband target signature is investigated. Target recognition of some simple wire targets using the extinction pulse technique demonstrate that it would be easier to fully excite all of the important resonances using a circular polarization basis with due consideration of the co- and cross-polarized target signatures.

HPLC enantioseparation of alkaloid malacitanine using fluorimetric/polarimetric detection

This work reports two methods developed for the separation and determination of the enantiomers of the new alkaloid malacitanine (MLC) and the determination of the enantiomeric purity in mixtures. First, the isomers were separated using a Chirex 3020 (250 mm × 4.6 mm, 5 μm) chiral column with a mobile phase of cyclohexane-1,2-dichloroethane-ethanol-trifluoroacetic acid (64:30:6:0.6, v/v/v/v) at a flow rate of 1 mL/min and fluorimetric detection. Obtained retention times were 12.4 and 15.9 min (+ and -) with a resolution Rs of 1.13. Relative standard deviations (RSDs) were 2.5 and 2.4% at the 0.5-μg level (four determinations). Second, a nonenantioselective procedure for the determination of enantiomeric purity of MLC using a Lichrospher ® Si-60 (250 mm × 5 mm, 5 μm) normal phase with a mobile phase of 100% ethanol at a flow rate of 0.9 mL/min coupled to two detectors in series, fluorimetric and polarimetric. RSD of 3.3% was obtained. Calculated enantiomeric purity by chiral chromatography gave 48.6% (-)-MLC in the near racemic product. Using polarimetric signal of the nonseparated enantiomers and comparing the slopes of the calibration curves (enantiomers) from the racemic product gave 47.8% (-)-MLC content. A study of accuracy of (-)-MLC gave recoveries from 98.3 to 100.7%.

GLACIER SURFACE MONITORING BY MAXIMIZING MUTUAL INFORMATION

Abstract. The contribution of Polarimetric Synthetic Aperture Radar (PolSAR) images compared with the single-channel SAR in terms of temporal scene characterization has been found and described to add valuable information in the literature. However, despite a number of recent studies focusing on single polarized glacier monitoring, the potential of polarimetry to estimate the surface velocity of glaciers has not been explored due to the complex mechanism of polarization through glacier/snow. In this paper, a new approach to the problem of monitoring glacier surface velocity is proposed by means of temporal PolSAR images, using a basic concept from information theory: Mutual Information (MI). The proposed polarimetric tracking method applies the MI to measure the statistical dependence between temporal polarimetric images, which is assumed to be maximal if the images are geometrically aligned. Since the proposed polarimetric tracking method is very powerful and general, it can be implemented into any kind of multivariate remote sensing data such as multi-spectral optical and single-channel SAR images. The proposed polarimetric tracking is then used to retrieve surface velocity of Aletsch glacier located in Switzerland and of Inyltshik glacier in Kyrgyzstan with two different SAR sensors; Envisat C-band (single polarized) and DLR airborne L-band (fully polarimetric) systems, respectively. The effect of number of channel (polarimetry) into tracking investigations demonstrated that the presence of snow, as expected, effects the location of the phase center in different polarization, such as glacier tracking with temporal HH compared to temporal VV channels. Shortly, a change in polarimetric signature of the scatterer can change the phase center, causing a question of how much of what I am observing is motion then penetration. In this paper, it is shown that considering the multi-channel SAR statistics, it is possible to optimize the separate these contributions.

Applying Bayesian Decision Classification to Pi-SAR Polarimetric Data for Detailed Extraction of the Geomorphologic and Structural Features of an Active Volcano

An understanding of the geomorphology and distribution of surface materials on an active volcano is crucial to characterize eruptions and mitigate volcanic hazards. For volcanoes, synthetic aperture radar (SAR) remote sensing is the only useful observation and monitoring technology that can be undertaken in any weather condition. This letter uses the data from one type of airborne SAR system termed polarimetric and interferometric airborne SAR and L-band microwaves to classify SAR imagery into geomorphologic units, based on a scattering mechanism, using the example of Mt. Sakurajima, a representative active volcano situated in southern Japan. This is accomplished by adopting a Bayesian decision classification (BDC) scheme applied to two polarimetric parameters, namely, entropy and the type of scattering mechanism, which are derived from Cloude-Pottier decomposition of full polarimetry. In spite of the thick vegetation cover, BDC can divide SAR imagery from Mt. Sakurajima into three geomorphologic units: volcanic cone, terrace, and foot. The suitability of the BDC classification of microwave sensor imagery-and its superiority over a traditional classification scheme, the K -means unsupervised classification-is confirmed by polarimetric signature analysis and ground-truth surveying that directly quantifies surface scattering.

Investigation of the capability of the Compact Polarimetry mode to Reconstruct Full Polarimetry mode using RADARSAT2 data

Recently, there has been growing interest in dual-pol systems that transmit one polarization and receive two polarizations. Souyris et al. proposed a DP mode called compact polarimetry (CP) which is able to reduce the complexity, cost, mass, and data rate of a SAR system while attempting to maintain many capabilities of a fully polarimetric system. This paper provides a comparison of the information content of full quad-pol data and the pseudo quad-pol data derived from compact polarimetric SAR modes. A pseudo-covariance matrix can be reconstructed following Souyris’s approach and is shown to be similar to the full polarimetric (FP) covariance matrix. Both the polarimetric signatures based on the kennaugh matrix and the Freeman and Durden decomposition in the context of this compact polarimetry mode are explored. The Freeman and Durden decomposition is used in our study because of its direct relationship to the reflection symmetry. We illustrate our results by using the polarimetric SAR images of Algiers city in Algeria acquired by the RadarSAT2 in C-band.

Comparison of polarimetric signatures of hail at S and C bands for different hail sizes

In this study, severe hail cases in Oklahoma/USA are investigated by analyzing the data simultaneously collected by two closely located polarimetric weather radars operating at S and C bands. Polarimetric radar variables measured in the presence of hail at C band are quite different from the ones at S band due to more pronounced effects of resonance scattering and much stronger impact of attenuation. The differences are particularly strong in melting hail below the freezing level, but they can be substantial even at higher altitudes where hail is dry or grows in wet regime. As a consequence, the algorithms for hail detection and determination of its size developed at S band can't be directly applied to C band. Differences between vertical profiles of radar reflectivity Z, differential reflectivity ZDR, and cross-correlation coefficient ρhv in hail-bearing parts of the storms have been examined for large and giant hail. It is shown that in the presence of hail, ZDR(C) is usually higher than ZDR(S) and ρhv(C)<ρhv(S). The height of radar resolution volume with respect to the freezing level has to be taken into account in polarimetric hail detection/sizing. It is also demonstrated that giant hail is commonly associated with pronounced depression of ρhv in the areas of hail generation above the freezing level and the corresponding drop in ρhv at C band is much stronger than at S band. These results are compared to C-band polarimetric data collected in hail-bearing thunderstorms in Austria, where additional small hail size reports are available.

Ensemble Kalman Filter Analyses of the 29–30 May 2004 Oklahoma Tornadic Thunderstorm Using One- and Two-Moment Bulk Microphysics Schemes, with Verification against Polarimetric Radar Data

AbstractThe performance of ensemble Kalman filter (EnKF) analysis is investigated for the tornadic supercell on 29–30 May 2004 in Oklahoma using a dual-moment (DM) bulk microphysics scheme in the Advanced Regional Prediction System (ARPS) model. The comparison of results using single-moment (SM) and DM microphysics schemes evaluates the benefits of using one over the other during storm analysis. Observations from a single operational Weather Surveillance Radar-1988 Doppler (WSR-88D) are assimilated and a polarimetric WSR-88D in Norman, Oklahoma (KOUN), is used to assess the quality of the analysis.Analyzed reflectivity and radial velocity in the SM and DM experiments compare favorably with independent radar observations in general. However, simulated polarimetric signatures obtained from analyses using a DM scheme agree significantly better with polarimetric signatures observed by KOUN in terms of the general structure, location, and intensity of the signatures than those generated from analyses using an SM scheme.These results demonstrate for the first time for a real supercell storm that EnKF data assimilation using a numerical model with an adequate microphysics scheme (i.e., a scheme that predicts at least two moments of the hydrometeor size distributions) is capable of producing polarimetric radar signatures similar to those seen in observations without directly assimilating polarimetric data. In such cases, the polarimetric data also serve as completely independent observations for the verification purposes.