Articles de revues : « Polarimetric signature »

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Takahashi, J., Y. Itoh, T. Matsuo, Y. Oasa, Y. P. Bach et M. Ishiguro. « Polarimetric signature of the oceans as detected by near-infrared Earthshine observations ». Astronomy & ; Astrophysics 653 (septembre 2021) : A99. http://dx.doi.org/10.1051/0004-6361/202039331.

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Context. The discovery of an extrasolar planet with an ocean has crucial importance in the search for life beyond Earth. The polarimetric detection of specularly reflected light from a smooth liquid surface is anticipated theoretically, though the polarimetric signature of Earth’s oceans has not yet been conclusively detected in disk-integrated planetary light. Aims. We aim to detect and measure the polarimetric signature of the Earth’s oceans. Methods. We conducted near-infrared polarimetry for lunar Earthshine and collected data on 32 nights with a variety of ocean fractions in the Earthshine-contributing region. Results. A clear positive correlation was revealed between the polarization degree and ocean fraction. We found hourly variations in polarization in accordance with rotational transition of the ocean fraction. The ratios of the variation to the typical polarization degree were as large as ~0.2–1.4. Conclusions. Our observations provide plausible evidence of the polarimetric signature attributed to Earth’s oceans. Near-infrared polarimetry may be considered a prospective technique in the search for exoplanetary oceans.

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Ryzhkov, Alexander V., Terry J. Schuur, Donald W. Burgess et Dusan S. Zrnic. « Polarimetric Tornado Detection ». Journal of Applied Meteorology 44, n^o 5 (1 mai 2005) : 557–70. http://dx.doi.org/10.1175/jam2235.1.

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Abstract Polarimetric radars are shown to be capable of tornado detection through the recognition of tornadic debris signatures that are characterized by the anomalously low cross-correlation coefficient ρhv and differential reflectivity ZDR. This capability is demonstrated for three significant tornadic storms that struck the Oklahoma City, Oklahoma, metropolitan area. The first tornadic debris signature, based on the measurements with the National Severe Storms Laboratory’s Cimarron polarimetric radar, was reported for a storm on 3 May 1999. Similar signatures were identified for two significant tornadic events during the Joint Polarization Experiment (JPOLE) in May 2003. The data from these storms were collected with a polarimetric prototype of the Next-Generation Weather Radar (NEXRAD). In addition to a small-scale debris signature, larger-scale polarimetric signatures that might be relevant to tornadogenesis were persistently observed in tornadic supercells. The latter signatures are likely associated with lofted light debris (leaves, grass, dust, etc.) in the inflow region and intense size sorting of hydrometeors in the presence of strong wind shear and circulation.

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Snyder, Jeffrey C., Howard B. Bluestein, Vijay Venkatesh et Stephen J. Frasier. « Observations of Polarimetric Signatures in Supercells by an X-Band Mobile Doppler Radar ». Monthly Weather Review 141, n^o 1 (1 janvier 2013) : 3–29. http://dx.doi.org/10.1175/mwr-d-12-00068.1.

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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.

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Vyas, A., et B. Sashtri. « SAR POLARIMETRIC SIGNATURES FOR URBAN TARGETS &ndash ; POLARIMETRIC SIGNATURE CALCULATION AND VISUALIZATION ». ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XXXIX-B7 (2 août 2012) : 535–40. http://dx.doi.org/10.5194/isprsarchives-xxxix-b7-535-2012.

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Kumjian, Matthew R., et Alexander V. Ryzhkov. « Polarimetric Signatures in Supercell Thunderstorms ». Journal of Applied Meteorology and Climatology 47, n^o 7 (1 juillet 2008) : 1940–61. http://dx.doi.org/10.1175/2007jamc1874.1.

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Abstract Data from polarimetric radars offer remarkable insight into the microphysics of convective storms. Numerous tornadic and nontornadic supercell thunderstorms have been observed by the research polarimetric Weather Surveillance Radar-1988 Doppler (WSR-88D) in Norman, Oklahoma (KOUN); additional storm data come from the Enterprise Electronics Corporation “Sidpol” C-band polarimetric radar in Enterprise, Alabama, as well as the King City C-band polarimetric radar in Ontario, Canada. A number of distinctive polarimetric signatures are repeatedly found in each of these storms. The forward-flank downdraft (FFD) is characterized by a signature of hail observed as near-zero ZDR and high ZHH. In addition, a shallow region of very high ZDR is found consistently on the southern edge of the FFD, called the ZDR “arc.” The ZDR and KDP columns and midlevel “rings” of enhanced ZDR and depressed ρHV are usually observed in the vicinity of the main rotating updraft and in the rear-flank downdraft (RFD). Tornado touchdown is associated with a well-pronounced polarimetric debris signature. Similar polarimetric features in supercell thunderstorms have been reported in other studies. The data considered here are taken from both S- and C-band radars from different geographic locations and during different seasons. The consistent presence of these features may be indicative of fundamental processes intrinsic to supercell storms. Hypotheses on the origins, as well as microphysical and dynamical interpretations of these signatures, are presented. Implications about storm morphology for operational applications are suggested.

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Johnson, Marcus, Youngsun Jung, Daniel T. Dawson et Ming Xue. « Comparison of Simulated Polarimetric Signatures in Idealized Supercell Storms Using Two-Moment Bulk Microphysics Schemes in WRF ». Monthly Weather Review 144, n^o 3 (16 février 2016) : 971–96. http://dx.doi.org/10.1175/mwr-d-15-0233.1.

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Abstract Microphysics parameterization becomes increasingly important as the model grid spacing increases toward convection-resolving scales. The performance of several partially or fully two-moment (2M) schemes within the Weather Research and Forecasting (WRF) Model, version 3.5.1, chosen because of their well-documented advantages over one-moment (1M) schemes, is evaluated with respect to their ability in producing the well-known polarimetric radar signatures found within supercell storms. Such signatures include the ZDR and KDP columns, the ZDR arc, the midlevel ZDR and ρHV rings, the hail signature in the forward-flank downdraft, and the KDP foot. Polarimetric variables are computed from WRF Model output using a polarimetric radar simulator. It is found that microphysics schemes with a 1M rimed-ice category are unable to simulate the ZDR arc, despite containing a 2M rain category. It is also found that a hail-like rimed-ice category (in addition to graupel) may be necessary to reproduce the observed hail signature. For the microphysics schemes that only contain a graupel-like rimed-ice category, only very wet graupel particles are able to reach the lowest model level, which did not adequately reduce ZDR in this signature. The most realistic signatures overall are found with microphysics schemes that are fully 2M with a separate hail category.

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Van Den Broeke, Matthew S. « Polarimetric Tornadic Debris Signature Variability and Debris Fallout Signatures ». Journal of Applied Meteorology and Climatology 54, n^o 12 (décembre 2015) : 2389–405. http://dx.doi.org/10.1175/jamc-d-15-0077.1.

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AbstractValues of polarimetric radar variables may vary substantially between and through tornadic debris signature (TDS) events. Tornadoes with higher intensity ratings are associated with higher average and extreme values of reflectivity factor at horizontal polarization ZHH and lower values of copolar cross-correlation coefficient ρhv. Although values of these variables often fluctuate through reported tornado life cycles, ZHH repeatably decreases and ρhv repeatably increases across the volume scan immediately following reported tornado demise. Land cover has a relatively small effect on values of the polarimetric variables within TDSs, although near-radar urban TDSs may exhibit relatively high ZHH values. TDS areal extent is typically larger aloft than near the surface, although this trend may reverse in the most intense tornadoes. Maximum altitude to which a TDS is visible is more strongly a function of tornado intensity than of land cover or ambient shear and instability. Debris often disappears once lofted but may also be observed to spread out downstream with the storm-relative flow or to fall out along the parent storm’s northwest flank in a debris fallout signature (DFS). DFS characteristics, although variable, most commonly include ZHH values of 30–35 dBZ, ρhv values of 0.60–0.80, and values of differential reflectivity ZDR that are repeatably near 0 dB.

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Andrić, Jelena, Matthew R. Kumjian, Dušan S. Zrnić, Jerry M. Straka et Valery M. Melnikov. « Polarimetric Signatures above the Melting Layer in Winter Storms : An Observational and Modeling Study ». Journal of Applied Meteorology and Climatology 52, n^o 3 (mars 2013) : 682–700. http://dx.doi.org/10.1175/jamc-d-12-028.1.

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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.

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Van Den Broeke, Matthew S., et Sabrina T. Jauernic. « Spatial and Temporal Characteristics of Polarimetric Tornadic Debris Signatures ». Journal of Applied Meteorology and Climatology 53, n^o 10 (octobre 2014) : 2217–31. http://dx.doi.org/10.1175/jamc-d-14-0094.1.

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AbstractNonmeteorological scatter, including debris lofted by tornadoes, may be detected using the polarimetric radar variables. For the 17 months from January 2012 to May 2013, radar data were examined for each tornado reported in the domain of an operational polarimetric Weather Surveillance Radar-1988 Doppler (WSR-88D). Characteristics of the tornadic debris signature (TDS) were recorded when a signature was present. Approximately 16% of all tornadoes reported in Storm Data were associated with a debris signature, and this proportion is shown to vary regionally. Signatures were more frequently seen with tornadoes that were rated higher on the enhanced Fujita (EF) scale, with tornadoes causing higher reported total property damage, with tornadoes that were closer to the radar and thus intercepted by the beam at lower altitude, and associated with tornadoes with greater total pathlength. Tornadic debris signatures were most common in spring, when more strong tornadoes occur, and in autumn, when natural debris is more available. Debris-signature areal extent is shown to increase consistently with EF-scale rating and tornado longevity. Vertical extent of a TDS is shown to be greatest for strong, long-lived tornadoes with large radii of damaging wind. Land cover is also shown to exhibit some control over TDS characteristics—in particular, a large percentage of tornadoes with substantial track over urban land cover exhibited a TDS and do so very quickly after reported tornadogenesis, as compared with tornadoes over other land-cover classifications. TDS characteristics over grassland and cropland tended to be similar.

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Griffin, Casey B., David J. Bodine et Robert D. Palmer. « Kinematic and Polarimetric Radar Observations of the 10 May 2010, Moore–Choctaw, Oklahoma, Tornadic Debris Signature ». Monthly Weather Review 145, n^o 7 (juillet 2017) : 2723–41. http://dx.doi.org/10.1175/mwr-d-16-0344.1.

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Tornadoes are capable of lofting large pieces of debris that present irregular shapes, near-random orientations, and a wide range of dielectric constants to polarimetric radars. The unique polarimetric signature associated with lofted debris is called the tornadic debris signature (TDS). While ties between TDS characteristics and tornado- and storm-scale kinematic processes have been speculated upon or investigated using photogrammetry and single-Doppler analyses, little work has been done to document the three-dimensional wind field associated with the TDS. Data collected by the Oklahoma City, Oklahoma (KTLX), and Norman, Oklahoma (KOUN), WSR-88D S-band radars as well as the University of Oklahoma’s (OU) Advanced Radar Research Center’s Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME) C-band radar are used to construct single- and dual-Doppler analyses of a tornadic supercell that produced an EF4 tornado near the towns of Moore and Choctaw, Oklahoma, on 10 May 2010. This study documents the spatial distribution of polarimetric radar variables and how each variable relates to kinematic fields such as vertical velocity and vertical vorticity. Special consideration is given to polarimetric signatures associated with subvortices within the tornado. An observation of negative differential reflectivity ([Formula: see text]) at the periphery of tornado subvortices is presented and discussed. Finally, dual-Doppler wind retrievals are compared to single-Doppler axisymmetric wind fields to illustrate the merits of each method.

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Pieraccini, M., M. Pisaneschi, L. Noferini et C. Atzeni. « Polarimetric radar signature of masonry walls ». NDT & ; E International 40, n^o 4 (juin 2007) : 271–74. http://dx.doi.org/10.1016/j.ndteint.2006.11.004.

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Richard, D. T., et S. S. Davis. « Lunar dust characterization by polarimetric signature ». Astronomy & ; Astrophysics 483, n^o 2 (26 mars 2008) : 643–49. http://dx.doi.org/10.1051/0004-6361:20079108.

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Picca, J., et A. Ryzhkov. « A Dual-Wavelength Polarimetric Analysis of the 16 May 2010 Oklahoma City Extreme Hailstorm ». Monthly Weather Review 140, n^o 4 (avril 2012) : 1385–403. http://dx.doi.org/10.1175/mwr-d-11-00112.1.

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A comparative analysis of a supercell hailstorm using simultaneous observations with S-band and C-band polarimetric radars supported by abundant ground-truth reports is presented in this study. The storm occurred on 16 May 2010 and produced a swath of extremely damaging hail across a large portion of the Oklahoma City, Oklahoma, metro area. Hail sizes over 10 cm in diameter and hail drifts upward of 1.5 m in height were reported. Both S-band (KOUN) and C-band [University of Oklahoma Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME)] polarimetric radars in Norman, Oklahoma, sampled the storm at ranges less than 60 km, so that high-resolution dual-wavelength polarimetric data were obtained. At C band, this analysis mostly presents raw Z and ZDR (due to problems with differential phase resulting from an incorrect censoring threshold in the examined case) while taking into account the possibility of attenuation in the interpretation of these data. Among the issues investigated in the study are the relation of hail size measured at the surface to the polarimetric signatures at both wavelengths, the difference between polarimetric signatures at the two wavelengths of hail aloft and near the surface (where melting hail is mixed with rain), and the three-body scatter spike (TBSS) signature associated with large hail.

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Nasr, Ayman H., et Hind Z. Abdelhamid. « POLARIMETRIC SIGNATURES IDENTIFICATION FOR DIFFERENT FEATURES IN RADARSAT-2 POLSAR IMAGE : A CASE STUDY OF HALAYIB AREA, EGYPT ». ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B7 (22 juin 2016) : 851–57. http://dx.doi.org/10.5194/isprs-archives-xli-b7-851-2016.

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In fully polarized SAR (PolSAR) data the returned signal from a target contains all polarizations. More information about this target may be inferred with respect to single-polarization. Distinct polarization separates targets due to its different backscattering responses. A Radarsat-2 PolSAR image acquired on December 2013 of part of Halayib area (Egypt) was used in this study. Polarimetric signatures for various features (Wadi deposits, Tonalite, Chlorite schist, and Radar penetrated areas) were derived and identified. Their Co-polarized and Cross-polarized signatures were generated, based on the calculation of the backscattered power at various ellipticity and orientation angles. Graphical 3D-representation of these features was provided and more details of their physical information are depicted according to their different polarization bases. The results illustrate that polarimetric signatures, obtained due to factors like surface roughness, dielectric constant and feature orientation, can be an effective representation for analyzing various features. The shape of the signature is significant and can also indicate the scattering mechanisms dominating the features response.

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Nasr, Ayman H., et Hind Z. Abdelhamid. « POLARIMETRIC SIGNATURES IDENTIFICATION FOR DIFFERENT FEATURES IN RADARSAT-2 POLSAR IMAGE : A CASE STUDY OF HALAYIB AREA, EGYPT ». ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B7 (22 juin 2016) : 851–57. http://dx.doi.org/10.5194/isprsarchives-xli-b7-851-2016.

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In fully polarized SAR (PolSAR) data the returned signal from a target contains all polarizations. More information about this target may be inferred with respect to single-polarization. Distinct polarization separates targets due to its different backscattering responses. A Radarsat-2 PolSAR image acquired on December 2013 of part of Halayib area (Egypt) was used in this study. Polarimetric signatures for various features (Wadi deposits, Tonalite, Chlorite schist, and Radar penetrated areas) were derived and identified. Their Co-polarized and Cross-polarized signatures were generated, based on the calculation of the backscattered power at various ellipticity and orientation angles. Graphical 3D-representation of these features was provided and more details of their physical information are depicted according to their different polarization bases. The results illustrate that polarimetric signatures, obtained due to factors like surface roughness, dielectric constant and feature orientation, can be an effective representation for analyzing various features. The shape of the signature is significant and can also indicate the scattering mechanisms dominating the features response.

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Jung, Youngsun, Ming Xue et Guifu Zhang. « Simulations of Polarimetric Radar Signatures of a Supercell Storm Using a Two-Moment Bulk Microphysics Scheme ». Journal of Applied Meteorology and Climatology 49, n^o 1 (1 janvier 2010) : 146–63. http://dx.doi.org/10.1175/2009jamc2178.1.

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Abstract A new general polarimetric radar simulator for nonhydrostatic numerical weather prediction (NWP) models has been developed based on rigorous scattering calculations using the T-matrix method for reflectivity, differential reflectivity, specific differential phase, and copolar cross-correlation coefficient. A continuous melting process accounts for the entire spectrum of varying density and dielectric constants. This simulator is able to simulate polarimetric radar measurements at weather radar frequency bands and can take as input the prognostic variables of high-resolution NWP model simulations using one-, two-, and three-moment microphysics schemes. The simulator was applied at 10.7-cm wavelength to a model-simulated supercell storm using a double-moment (two moment) bulk microphysics scheme to examine its ability to simulate polarimetric signatures reported in observational studies. The simulated fields exhibited realistic polarimetric signatures that include ZDR and KDP columns, ZDR arc, midlevel ZDR and ρhυ rings, hail signature, and KDP foot in terms of their general location, shape, and strength. The authors compared the simulation with one employing a single-moment (SM) microphysics scheme and found that certain signatures, such as ZDR arc, midlevel ZDR, and ρhυ rings, cannot be reproduced with the latter. It is believed to be primarily caused by the limitation of the SM scheme in simulating the shift of the particle size distribution toward larger/smaller diameters, independent of mixing ratio. These results suggest that two- or higher-moment microphysics schemes should be used to adequately describe certain important microphysical processes. They also demonstrate the utility of a well-designed radar simulator for validating numerical models. In addition, the simulator can also serve as a training tool for forecasters to recognize polarimetric signatures that can be reproduced by advanced NWP models.

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Wang, Yadong, et Tian-You Yu. « Novel Tornado Detection Using an Adaptive Neuro-Fuzzy System with S-Band Polarimetric Weather Radar ». Journal of Atmospheric and Oceanic Technology 32, n^o 2 (février 2015) : 195–208. http://dx.doi.org/10.1175/jtech-d-14-00096.1.

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AbstractTornado debris signatures (TDS) exhibited in polarimetric measurements have the potential to facilitate tornado detection. The upgrade of the network of S-band Weather Surveillance Radar-1988 Doppler (WSR-88D) to dual polarization was completed recently. Therefore, it is timely to develop a tornado detection algorithm that capitalizes on TDS and integrates with other existing signatures observed in the velocity (shear signature) and Doppler spectrum (spectral signature) fields. In this work, the analysis indicates that TDS are not always present with shear and spectral signatures. A neuro-fuzzy tornado detection algorithm (NFTDA) using the Sugeno fuzzy inference system is developed to consider the strength of different tornado signatures that are characterized by operationally available data of differential reflectivity, cross-correlation coefficient, velocity difference, and spectrum width with the goal of reliable and robust detection. The performance is further optimized using a training procedure based on a neural network. The performance of NFTDA is evaluated using polarimetric WSR-88D data from 17 tornadoes with enhanced Fujita (EF) scale ratings ranging from EF-0 to EF-4 and distance from 16 to 133 km to the radar. NFTDA performs well with the probability of detection (POD), false alarm ratio (FAR), and critical success index (CSI) of 86%, 11%, and 78%, respectively. Moreover, a computationally efficient method is introduced to analyze the sensitivity of the tornado signatures. It is demonstrated that even though TDS play a less important role than the other two signatures, TDS can help improve the detection, especially during the later stage of a tornado, when the shear and spectral signatures become weaker.

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Trömel, Silke, Alexander V. Ryzhkov, Pengfei Zhang et Clemens Simmer. « Investigations of Backscatter Differential Phase in the Melting Layer ». Journal of Applied Meteorology and Climatology 53, n^o 10 (octobre 2014) : 2344–59. http://dx.doi.org/10.1175/jamc-d-14-0050.1.

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AbstractBackscatter differential phase δ within the melting layer has been identified as a reliably measurable but still underutilized polarimetric variable. Polarimetric radar observations at X band in Germany and S band in the United States are presented that show maximal observed δ of 8.5° at X band but up to 70° at S band. Dual-frequency observations at X and C band in Germany and dual-frequency observations at C and S band in the United States are compared to explore the regional frequency dependencies of the δ signature. Theoretical simulations based on usual assumptions about the microphysical composition of the melting layer cannot reproduce the observed large values of δ at the lower-frequency bands and also underestimate the enhancements in differential reflectivity ZDR and reductions in the cross-correlation coefficient ρhυ. Simulations using a two-layer T-matrix code and a simple model for the representation of accretion can, however, explain the pronounced δ signatures at S and C bands in conjunction with small δ at X band. The authors conclude that the δ signature bears information about microphysical accretion and aggregation processes in the melting layer and the degree of riming of the snowflakes aloft.

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Rogers, George W., Houra Rais et William L. Cameron. « Polarimetric SAR Signature Detection Using the Cameron Decomposition ». IEEE Transactions on Geoscience and Remote Sensing 52, n^o 1 (janvier 2014) : 690–700. http://dx.doi.org/10.1109/tgrs.2013.2243737.

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Kumjian, Matthew R., Alexander V. Ryzhkov, Heather D. Reeves et Terry J. Schuur. « A Dual-Polarization Radar Signature of Hydrometeor Refreezing in Winter Storms ». Journal of Applied Meteorology and Climatology 52, n^o 11 (novembre 2013) : 2549–66. http://dx.doi.org/10.1175/jamc-d-12-0311.1.

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AbstractPolarimetric radar measurements in winter storms that produce ice pellets have revealed a unique signature that is indicative of ongoing hydrometeor refreezing. This refreezing signature is observed within the low-level subfreezing air as an enhancement of differential reflectivity ZDR and specific differential phase KDP and a decrease of radar reflectivity factor at horizontal polarization ZH and copolar correlation coefficient ρhv. It is distinct from the overlying melting-layer “brightband” signature and suggests that unique microphysical processes are occurring within the layer of hydrometeor refreezing. The signature is analyzed for four ice-pellet cases in central Oklahoma as observed by two polarimetric radars. A statistical analysis is performed on the characteristics of the refreezing signature for a case of particularly long duration. Several hypotheses are presented to explain the appearance of the signature, along with a summary of the pros and cons for each. It is suggested that preferential freezing of small drops and local ice generation are plausible mechanisms for the appearance of the ZDR and KDP enhancements. Polarimetric measurements and scattering calculations are used to retrieve microphysical information to explore the validity of the hypotheses. The persistence and repetitiveness of the signature suggest its potential use in operational settings to diagnose the transition between freezing rain and ice pellets.

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Canabal-Carbia, Mónica, Adriana R. Sánchez-Montes, Carla Rodríguez, Irene Estévez, Jordi Luque, Teresa Garnatje, Juan Campos et Angel Lizana. « Inspection of plant pathologies through pseudocolored images based on polarimetric basis ». EPJ Web of Conferences 287 (2023) : 03004. http://dx.doi.org/10.1051/epjconf/202328703004.

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The study of the interaction of biological tissue with polarized light leads to relevant information of physical properties (dichroism, retardance and depolarization) of samples. Polarimetric analysis of different characteristics in tissues is useful for applications such us tissue classification, contrast enhancement or pathology detection. By means of polarimetric imaging techniques we can characterize the polarimetric signature of biological samples in a noninvasive and nondestructive way. We have found that depolarization information is of special interest in turbid media such as plant tissue. In this manuscript we use polarimetric observables for plant inspection. In particular, we provide enhanced visualization of certain plant pathologies by constructing depolarization based pseudocolored images of pathological leaves where the pathological areas are revealed.

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Porzycka-Strzelczyk, Stanisława, Jacek Strzelczyk, Kamil Szostek, Maciej Dwornik, Andrzej Leśniak, Justyna Bała et Anna Franczyk. « Information Extraction from Satellite-Based Polarimetric SAR Data Using Simulated Annealing and SIRT Methods and GPU Processing ». Energies 15, n^o 1 (22 décembre 2021) : 72. http://dx.doi.org/10.3390/en15010072.

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The main goal of this research was to propose a new method of polarimetric SAR data decomposition that will extract additional polarimetric information from the Synthetic Aperture Radar (SAR) images compared to other existing decomposition methods. Most of the current decomposition methods are based on scattering, covariance or coherence matrices describing the radar wave-scattering phenomenon represented in a single pixel of an SAR image. A lot of different decomposition methods have been proposed up to now, but the problem is still open since it has no unique solution. In this research, a new polarimetric decomposition method is proposed that is based on polarimetric signature matrices. Such matrices may be used to reveal hidden information about the image target. Since polarimetric signatures (size 18 × 9) are much larger than scattering (size 2 × 2), covariance (size 3 × 3 or 4 × 4) or coherence (size 3 × 3 or 4 × 4) matrices, it was essential to use appropriate computational tools to calculate the results of the proposed decomposition method within an acceptable time frame. In order to estimate the effectiveness of the presented method, the obtained results were compared with the outcomes of another method of decomposition (Arii decomposition). The conducted research showed that the proposed solution, compared with Arii decomposition, does not overestimate the volume-scattering component in built-up areas and clearly separates objects within the mixed-up areas, where both building, vegetation and surfaces occur.

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Van Den Broeke, Matthew S. « Polarimetric Radar Observations of Biological Scatterers in Hurricanes Irene (2011) and Sandy (2012) ». Journal of Atmospheric and Oceanic Technology 30, n^o 12 (1 décembre 2013) : 2754–67. http://dx.doi.org/10.1175/jtech-d-13-00056.1.

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Abstract Biological scatterers, consisting of birds and insects, may become trapped near the circulation center of tropical cyclones, particularly if a well-developed eyewall is present. These scatterers may be observed using weather radar, where they may appear to the radar operator as areas of light precipitation. Polarimetric radar characteristics of these scatterers, informed by additional observations of known bioscatter, include a combination of very high differential reflectivity (3–7.9 dB) and very low copolar correlation coefficient (0.3–0.8). Polarimetric radar observations of bioscatter are presented for Hurricane Irene (2011) and Hurricane Sandy (2012). In these storms, the bioscatter signature first appeared at the 0.5° elevation angle at a distance of 100–120 km from the radar. The signature appeared on successively higher tilts as the circulation center neared the radar, and its areal coverage in constant altitude plan position indicator (CAPPI) slices was primarily governed by the distribution of convection in the eye and by the timing of landfall. The highest altitude at which the signature appears may represent the inversion level within certain tropical cyclone eyes. For Hurricane Irene, inland observations of oceanic bird species support biological transport. Knowledge of the bioscatter signature has value to meteorologists monitoring tropical cyclones within the range of a polarimetric radar, possible value for estimating inversion height changes within the eyes of well-structured tropical cyclones, and value to biologists who wish to estimate the magnitude of biological transport in tropical cyclones.

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Bondur, V. G., T. N. Chimitdorzhiev, A. V. Dmitriev et P. N. Dagurov. « Spatial anisotropy assessment of the forest vegetation heterogeneity at various azimuth angles of the radar polarimetric sensing ». Исследования Земли из Космоса, n^o 3 (20 juin 2019) : 92–103. http://dx.doi.org/10.31857/s0205-96142019392-103.

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The results of studies to assess the texture of L- and C-band radar polarimetric images obtained from SIR-C and ALOS PALSAR-1 satellites for the analysis of forest vegetation characteristics using different signatures are summarized. A fractal polarization signature is proposed for the study, which allows to estimate the spatial anisotropy of forest vegetation inhomogeneities at different azimuthal angles of radar sensing. In addition, the signature of lacunarity is suggested as a tool for qualitative evaluation of the angular distribution of tree branches. The heterogeneities of forest vegetation at the test site near the Baikal Lake have been estimated based on the results of the analysis of fractal dimension and lacunarity at different states of the polarization ellipse.

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Kumjian, Matthew R., Dana M. Tobin, Mariko Oue et Pavlos Kollias. « Microphysical Insights into Ice Pellet Formation Revealed by Fully Polarimetric Ka-Band Doppler Radar ». Journal of Applied Meteorology and Climatology 59, n^o 10 (1 octobre 2020) : 1557–80. http://dx.doi.org/10.1175/jamc-d-20-0054.1.

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AbstractFully polarimetric scanning and vertically pointing Doppler spectral data from the state-of-the-art Stony Brook University Ka-band Scanning Polarimetric Radar (KASPR) are analyzed for a long-duration case of ice pellets over central Long Island in New York from 12 February 2019. Throughout the period of ice pellets, a classic refreezing signature was present, consisting of a secondary enhancement of differential reflectivity ZDR beneath the melting layer within a region of decreasing reflectivity factor at horizontal polarization ZH and reduced copolar correlation coefficient ρhv. The KASPR radar data allow for evaluation of previously proposed hypotheses to explain the refreezing signature. It is found that, upon entering a layer of locally generated columnar ice crystals and undergoing contact nucleation, smaller raindrops preferentially refreeze into ice pellets prior to the complete freezing of larger drops. Refreezing particles exhibit deformations in shape during freezing, leading to reduced ρhv, reduced co-to-cross-polar correlation coefficient ρxh, and enhanced linear depolarization ratio, but these shape changes do not explain the ZDR signature. The presence of columnar ice crystals, though apparently crucial for instigating the refreezing process, does not contribute enough backscattered power to affect the ZDR signature, either.

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Bodine, David J., Robert D. Palmer et Guifu Zhang. « Dual-Wavelength Polarimetric Radar Analyses of Tornadic Debris Signatures ». Journal of Applied Meteorology and Climatology 53, n^o 2 (février 2014) : 242–61. http://dx.doi.org/10.1175/jamc-d-13-0189.1.

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AbstractStatistical properties of tornado debris signatures (TDSs) are investigated using S- and C-band polarimetric radar data with comparisons to damage surveys and satellite imagery. Close proximity of the radars to the 10 May 2010 Moore–Oklahoma City, Oklahoma, tornado that was rated as a 4 on the enhanced Fujita scale (EF4) provides a large number of resolution volumes, and good temporal and spatial matching for dual-wavelength comparisons. These comparisons reveal that S-band TDSs exhibit a higher radar reflectivity factor (ZHH) and copolar cross-correlation coefficient (ρhv) than do C-band TDSs. Higher S-band ρhv may result from a smaller ratio of non-Rayleigh scatterers to total scatterers due to the smaller electrical sizes of debris and, consequently, reduced resonance effects. A negative ZDR signature is observed at 350 m AGL at both the S and C bands as the tornado passes over a vegetated area near a large body of water. Another interesting signature is a positive (negative) shift in propagation differential phase (ΦDP) at S band (C band), which could result from increased phase folding at C band. With increasing height above 350 m AGL, the S- and C-band ZHH decreases and ρhv increases, indicating a decrease in debris size. To investigate relationships between polarimetric variables and tornado wind fields, range profiles of radial and tangential wind speeds are obtained using two radars. Velocity profiles reveal radial divergence within vortex core flow through 700 m AGL collocated with the TDS. Formation of a weak-echo hole and higher ρhv in the vortex center aloft suggests debris centrifuging, outward motion of scatterers due to radial divergence (i.e., two-cell vortex flow), or both.

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Schiavulli, Domenico, Ali Ghavidel, Adriano Camps et Maurizio Migliaccio. « GNSS-R Wind-Dependent Polarimetric Signature Over the Ocean ». IEEE Geoscience and Remote Sensing Letters 12, n^o 12 (décembre 2015) : 2374–78. http://dx.doi.org/10.1109/lgrs.2015.2477685.

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Lee, J. S., E. Krogager, T. L. Ainsworth et W. M. Boerner. « Polarimetric Analysis of Radar Signature of a Manmade Structure ». IEEE Geoscience and Remote Sensing Letters 3, n^o 4 (octobre 2006) : 555–59. http://dx.doi.org/10.1109/lgrs.2006.879564.

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Pilorz, Wojciech, et Ewa Łupikasza. « Radar reflectivity signatures and possible lead times of warnings for very large hail in Poland based on data from 2007-2015 ». Environmental & ; Socio-economic Studies 8, n^o 3 (1 septembre 2020) : 34–47. http://dx.doi.org/10.2478/environ-2020-0016.

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AbstractHail involving very large hailstones (maximum diameter ≥ 5 cm), is a rare but very hazardous phenomenon in Poland, and can be forecast using reflectivity signatures. Every year, Poland experiences from one to over a dozen storms with such large hailstones. Despite the current recommendations regarding polarimetric techniques used in hail risk monitoring, Poland does not have a fully polarimetric radar network. Therefore it is essential to check hail detection capabilities using only reflectivity techniques based on individual radar systems involving hail detection algorithms such as Waldvogel et al. (1979) or Vertically Integrated Liquid thresholds connected with manual signature analysis to get better warning decisions. This study is aimed to determine the reflectivity features, thresholds and lead times for nowcasting of severe storms with very large hailstones in Poland, using data from the Polish radar system and from the European Severe Weather Database for the period 2007–2015. Most incidents involving very large hailstones were linked to supercell storms with distinctive reflectivity signatures, however, some storms with extremely large hailstones presented very poorly developed signatures. These signatures enabled the prediction of hail involving very large hailstones approximately 29 minutes before it fell. The Lemon (1980) criterion and WER were found to be the best hail predictors for Polish radar system conditions.

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Chael, Andrew, Alexandru Lupsasca, George N. Wong et Eliot Quataert. « Black Hole Polarimetry I. A Signature of Electromagnetic Energy Extraction ». Astrophysical Journal 958, n^o 1 (1 novembre 2023) : 65. http://dx.doi.org/10.3847/1538-4357/acf92d.

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Abstract In 1977, Blandford and Znajek showed that the electromagnetic field surrounding a rotating black hole can harvest its spin energy and use it to power a collimated astrophysical jet, such as the one launched from the center of the elliptical galaxy M87. Today, interferometric observations with the Event Horizon Telescope (EHT) are delivering high-resolution, event-horizon-scale, polarimetric images of the supermassive black hole M87* at the jet launching point. These polarimetric images offer an unprecedented window into the electromagnetic field structure around a black hole. In this paper, we show that a simple polarimetric observable—the phase ∠β 2 of the second azimuthal Fourier mode of the linear polarization in a near-horizon image—depends on the sign of the electromagnetic energy flux and therefore provides a direct probe of black hole energy extraction. In Boyer–Lindquist coordinates, the Poynting flux for axisymmetric electromagnetic fields is proportional to the product B ϕ B r . The phase ∠β 2 likewise depends on the ratio B ϕ /B r , thereby enabling an observer to determine the direction of electromagnetic energy flow in the near-horizon environment experimentally. Data from the 2017 EHT observations of M87* are consistent with electromagnetic energy outflow. Currently envisioned multifrequency observations of M87* will achieve higher dynamic range and angular resolution, and hence deliver measurements of ∠β 2 closer to the event horizon as well as better constraints on Faraday rotation. Such observations will enable a definitive test for energy extraction from the black hole M87*.

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Kumjian, Matthew R., et Alexander V. Ryzhkov. « Storm-Relative Helicity Revealed from Polarimetric Radar Measurements ». Journal of the Atmospheric Sciences 66, n^o 3 (1 mars 2009) : 667–85. http://dx.doi.org/10.1175/2008jas2815.1.

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Abstract The dual-polarization radar variables are especially sensitive to the microphysical processes of melting and size sorting of precipitation particles. In deep convective storms, polarimetric measurements of such processes can provide information about the airflow in and around the storm that may be used to elucidate storm behavior and evolution. Size sorting mechanisms include differential sedimentation, vertical transport, strong rotation, and wind shear. In particular, winds that veer with increasing height typical of supercell environments cause size sorting that is manifested as an enhancement of differential reflectivity (ZDR) along the right or inflow edge of the forward-flank downdraft precipitation echo, which has been called the ZDR arc signature. In some cases, this shear profile can be augmented by the storm inflow. It is argued that the magnitude of this enhancement is related to the low-level storm-relative environmental helicity (SRH) in the storm inflow. To test this hypothesis, a simple numerical model is constructed that calculates trajectories for raindrops based on their individual sizes, which allows size sorting to occur. The modeling results indicate a strong positive correlation between the maximum ZDR in the arc signature and the low-level SRH, regardless of the initial drop size distribution aloft. Additional observational evidence in support of the conceptual model is presented. Potential changes in the ZDR arc signature as the supercell evolves and the low-level mesocyclone occludes are described.

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Tobin, Dana M., et Matthew R. Kumjian. « Polarimetric Radar and Surface-Based Precipitation-Type Observations of Ice Pellet to Freezing Rain Transitions ». Weather and Forecasting 32, n^o 6 (8 novembre 2017) : 2065–82. http://dx.doi.org/10.1175/waf-d-17-0054.1.

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Abstract Recent studies document a polarimetric radar signature of refreezing. The signature is characterized by a low-level enhancement in differential reflectivity ZDR and a decrease in the copolar correlation coefficient ρhv within a region of decreasing radar reflectivity factor at horizontal polarization ZH toward the ground, called the refreezing layer (RFL). The evolution of the signature is examined during three winter storms in which the surface precipitation-type transitions from ice pellets to freezing rain. A modified quasi-vertical profile (QVP) technique is developed, which creates inverse-distance-weighted profiles using all available polarimetric data within a specified range from the radar location. Using this new technique reveals that the RFL descends in time prior to the transition from ice pellets to freezing rain and intersects the ground at the approximate transition time. Transition times are estimated using both crowdsourced and automated precipitation-type reports within a specified domain around the radar. These radar-estimated transition times are compared to a recently developed precipitation-classification algorithm based on Rapid Refresh (RAP) model wet-bulb temperature Tw profiles to explore potential benefits of analyzing QVPs during transition events. The descent of the RFL in the cases analyzed herein is related to low-level warm-air advection (WAA). A simple method for forecasting the transition time using QVPs is presented for cases of constant WAA. The repeatability of the refreezing signature’s descent in ice pellet to freezing rain transition events suggests the potential for its use in operational settings to create or modify short-term forecasts.

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Van Den Broeke, Matthew S., Dana M. Tobin et Matthew R. Kumjian. « Polarimetric Radar Observations of Precipitation Type and Rate from the 2–3 March 2014 Winter Storm in Oklahoma and Arkansas ». Weather and Forecasting 31, n^o 4 (7 juillet 2016) : 1179–96. http://dx.doi.org/10.1175/waf-d-16-0011.1.

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Abstract A powerful winter storm affected the south-central United States in early March 2014, accompanied by elevated convective cells with hail and high rates of sleet, freezing rain, and snow. During portions of the event the thermal profile exhibited a shallow surface cold layer and warm, unstable air aloft. Precipitation falling into the cold layer refroze into ice pellets and was accompanied by a polarimetric refreezing signature and numerous crowdsourced surface ice pellet reports. Quasi-vertical profiles of the polarimetric variables indicated an enhanced reflectivity factor ZHH below the melting layer bright band and enhanced low-level differential reflectivity ZDR values coincident with surface ice pellet reports. Freezing rain rate was highest in areas with high ZHH and specific differential phase KDP values at low levels. High snow rates were most closely associated with 1- and 1.5-km ZHH values, though KDP and ZDR also appeared to show some ability to distinguish high snow rate. Numerous elevated convective cells contained rotating updrafts that appeared to contribute to storm longevity and intensity. Most contained well-defined ZDR maxima or columns and relatively high base-scan ZDR values. Several contained polarimetric signatures consistent with heavy mixed-phase precipitation and hail; social media reports indicated that large hail was produced by some of the storms.

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Bukovčić, Petar, Dušan Zrnić et Guifu Zhang. « Winter Precipitation Liquid–Ice Phase Transitions Revealed with Polarimetric Radar and 2DVD Observations in Central Oklahoma ». Journal of Applied Meteorology and Climatology 56, n^o 5 (mai 2017) : 1345–63. http://dx.doi.org/10.1175/jamc-d-16-0239.1.

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AbstractObservations and analysis of an ice–liquid phase precipitation event, collected with an S-band polarimetric KOUN radar and a two-dimensional video disdrometer (2DVD) in central Oklahoma on 20 January 2007, are presented. Using the disdrometer measurements, precipitation is classified either as ice pellets or rain/freezing rain. The disdrometer observations showed fast-falling and slow-falling particles of similar size. The vast majority (>99%) were fast falling with observed velocities close to those of raindrops with similar sizes. In contrast to the smaller particles (<1 mm in diameter), bigger ice pellets (>1.5 mm) were relatively easy to distinguish because their shapes differ from the raindrops. The ice pellets were challenging to detect by looking at conventional polarimetric radar data because of the localized and patchy nature of the ice phase and their occurrence close to the ground. Previously published findings referred to cases in which ice pellet areas were centered on the radar location and showed a ringlike structure of enhanced differential reflectivity ZDR and reduced copolar correlation coefficient ρhv and horizontal reflectivity ZH in PPI images. In this study, a new, unconventional way of looking at polarimetric radar data is introduced: slanted vertical profiles (SVPs) at low (0°–1°) radar elevations. From the analysis of the localized and patchy structures using SVPs, the polarimetric refreezing signature, reflected in local enhancement in ZDR and reduction in ZH and ρhv, became much more evident. Model simulations of sequential drop freezing using Marshall–Palmer DSDs along with the observations suggest that preferential freezing of small drops may be responsible for the refreezing polarimetric signature, as suggested in previous studies.

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McKeown, Katherine E., Michael M. French, Kristofer S. Tuftedal, Darrel M. Kingfield, Howard B. Bluestein, Dylan W. Reif et Zachary B. Wienhoff. « Rapid-Scan and Polarimetric Radar Observations of the Dissipation of a Violent Tornado on 9 May 2016 near Sulphur, Oklahoma ». Monthly Weather Review 148, n^o 9 (1 septembre 2020) : 3951–71. http://dx.doi.org/10.1175/mwr-d-20-0033.1.

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Abstract Rapid-scan polarimetric data analysis of the dissipation of a likely violent supercell tornado that struck near Sulphur, Oklahoma, on 9 May 2016 is presented. The Rapid X-band Polarimetric Radar was used to obtain data of the tornado at the end of its mature phase and during its entire dissipation phase. The analysis is presented in two parts: dissipation characteristics of the tornadic vortex signature (TVS) associated with the tornado and storm-scale polarimetric features that may be related to processes contributing to tornado dissipation. The TVS exhibited near-surface radial velocities exceeding 100 m s−1 multiple times at the end of its mature phase, and then underwent a two-phased dissipation. Initially, decreases in near-surface intensity occurred rapidly over a ~5-min period followed by a slower decline in intensity that lasted an additional ~12 min. The dissipation of the TVS in time and height in the lowest 2 km above radar level and oscillatory storm-relative motion of the TVS also are discussed. Using polarimetric data, a well-defined low reflectivity ribbon is investigated for its vertical development, evolution, and relationship to the large tornadic debris signature (TDS) collocated with the TVS. The progression of the TDS during dissipation also is discussed with a focus on the presence of several bands of reduced copolar correlation coefficient that extend away from the main TDS and the eventual erosion of the TDS as the tornado dissipated. Finally, TVS and polarimetric data are combined to argue for the importance of a possible internal rear-flank downdraft momentum surge in contributing to the initial rapid dissipation of the tornado.

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Griffin, Erica M., Terry J. Schuur, Alexander V. Ryzhkov, Heather D. Reeves et Joseph C. Picca. « A Polarimetric and Microphysical Investigation of the Northeast Blizzard of 8–9 February 2013 ». Weather and Forecasting 29, n^o 6 (1 décembre 2014) : 1271–94. http://dx.doi.org/10.1175/waf-d-14-00056.1.

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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.

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Carlin, Jacob T., et Alexander V. Ryzhkov. « Estimation of Melting-Layer Cooling Rate from Dual-Polarization Radar : Spectral Bin Model Simulations ». Journal of Applied Meteorology and Climatology 58, n^o 7 (juillet 2019) : 1485–508. http://dx.doi.org/10.1175/jamc-d-18-0343.1.

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AbstractDiabatic cooling from hydrometeor phase changes in the stratiform melting layer is of great interest to both operational forecasters and modelers for its societal and dynamical consequences. Attempts to estimate the melting-layer cooling rate typically rely on either the budgeting of hydrometeor content estimated from reflectivity Z or model-generated lookup tables scaled by the magnitude of Z in the bright band. Recent advances have been made in developing methods to observe the unique polarimetric characteristics of melting snow and the additional microphysical information they may contain. However, to date no work has looked at the thermodynamic information available from the polarimetric radar brightband signature. In this study, a one-dimensional spectral bin model of melting snow and a coupled polarimetric operator are used to study the relation between the polarimetric radar bright band and the melting-layer cooling rate. Simulations using a fixed particle size distribution (PSD) and variable environmental conditions show that the height and thickness of the bright band and the maximum brightband Z and specific differential phase shift are all sensitive to the ambient environment, while the differential reflectivity is relatively insensitive. Additional simulations of 2700 PSDs based on in situ observations above the melting layer indicate that the maximum Z, , and within the melting layer are poorly correlated with the maximum cooling rate while is strongly correlated. Finally, model simulations suggest that, in addition to riming, concurrent changes in aggregation and precipitation intensity and the associated cooling may plausibly cause observed sagging brightband signatures.

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Schrom, Robert S., Matthew R. Kumjian et Yinghui Lu. « Polarimetric Radar Signatures of Dendritic Growth Zones within Colorado Winter Storms ». Journal of Applied Meteorology and Climatology 54, n^o 12 (décembre 2015) : 2365–88. http://dx.doi.org/10.1175/jamc-d-15-0004.1.

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AbstractX-band polarimetric radar observations of winter storms in northeastern Colorado on 20–21 February, 9 March, and 9 April 2013 are examined. These observations were taken by the Colorado State University–University of Chicago–Illinois State Water Survey (CSU-CHILL) radar during the Front Range Orographic Storms (FROST) project. The polarimetric radar moments of reflectivity factor at horizontal polarization ZH, differential reflectivity ZDR, and specific differential phase KDP exhibited a range of signatures at different times near the −15°C temperature level favored for dendritic ice crystal growth. In general, KDP was enhanced in these regions with ZDR decreasing and ZH increasing toward the ground, suggestive of aggregation (or riming). The largest ZDR values (~3.5–5.5 dB) were observed during periods of significant low-level upslope flow. Convective features observed when the upslope flow was weaker had the highest KDP (>1.5° km−1) and ZH (>20 dBZ) values. Electromagnetic scattering calculations using the generalized multiparticle Mie method were used to determine whether these radar signatures were consistent with dendrites. Particle size distributions (PSDs) of dendrites were retrieved for a variety of cases using these scattering calculations and the radar observations. The PSDs derived using stratiform precipitation observations were found to be reasonably consistent with previous PSD observations. PSDs derived where riming may have occurred likely had errors and deviated significantly from these previous PSD observations. These results suggest that this polarimetric radar signature may therefore be useful in identifying regions of rapidly collecting dendrites, after considering the effects of riming on the radar variables.

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Palucki, Jennifer L., Michael I. Biggerstaff, Donald R. MacGorman et Terry Schuur. « Comparison between Low-Flash and Non-Lightning-Producing Convective Areas within a Mature Mesoscale Convective System ». Weather and Forecasting 26, n^o 4 (1 août 2011) : 468–86. http://dx.doi.org/10.1175/waf-d-10-05012.1.

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Abstract Two small multicellular convective areas within a larger mesoscale convective system that occurred on 20 June 2004 were examined to assess vertical motion, radar reflectivity, and dual-polarimetric signatures between flash and non-flash-producing convection. Both of the convective areas had similar life cycles and general structures. Yet, one case produced two flashes, one of which may have been a cloud-to-ground flash, while the other convective area produced no flashes. The non-lightning-producing case had a higher peak reflectivity up to 6 km. Hence, if a reflectivity-based threshold were used as a precursor to lightning, it would have yielded misleading results. The peak upward motion in the mixed-phase region for both cases was 8 m s−1 or less. However, the lightning-producing storm contained a wider region where the updraft exceeded 5 m s−1. Consistent with the broader updraft region, the lightning-producing case exhibited a distinct graupel signature over a broader region than the non-lightning-producing convection. Slight differences in vertical velocity affected the quantity of graupel present in the mixed-phase region, thereby providing the subtle differences in polarimetric signatures that were associated with lightning activity. If the results here are generally applicable, then graupel volume may be a better precursor to a lightning flash than radar reflectivity. With the dual-polarimetric upgrade to the national observing radar network, it should be possible to better distinguish between lightning- and non-lightning-producing areas in weak convective systems that pose a potential safety hazard to the public.

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Van Den Broeke, Matthew S. « Bioscatter Characteristics Related to Inversion Variability in Atlantic Basin Tropical Cyclones ». Earth Interactions 26, n^o 1 (janvier 2022) : 28–38. http://dx.doi.org/10.1175/ei-d-21-0010.1.

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Abstract Tropical cyclones (TCs) routinely transport organisms at their centers of circulation. The TC center of circulation is also often marked by an inversion, and the height of the inversion base may change as the TC intensifies or weakens. In this study, a dataset of 49 dropsonde-measured inversions in 20 separate Atlantic Ocean TCs is compared with spatiotemporally collocated polarimetric radar measurements of bioscatter. Bioscatter signature maximum altitude is found to be a function of temperature lapse rate across the inversion base (r = 0.473), and higher inversion bases were generally associated with denser bioscatter signatures, especially when strong hurricanes (minimum pressure < 950 hPa) were considered (r = 0.601). Characteristics of the bioscatter signature had some skill in predicting TC inversion characteristics (adjusted r2 of 16%–40%), although predictability was increased when TC intensity was also included as a predictor (adjusted r2 of 40%–59%). These results indicate promise for using the bioscatter signature to monitor the TC inversion and represent an example of a situation in which the behavior of organisms in the airspace may be indicative of ongoing atmospheric processes. Significance Statement Tropical cyclone centers of circulation are often associated with an inversion, the base of which changes altitude with system strengthening and weakening. They may also contain a radar-observable bioscatter signature. In this study, we wanted to determine how the bioscatter signature relates to inversion characteristics for the benefit of meteorologists and biologists. Bioscatter signature characteristics were related to strength of the temperature and dewpoint lapse rates across the inversion base, and deeper/denser bioscatter signatures were typically associated with higher inversion bases. The findings suggest that trends in tropical cyclone inversion characteristics could be remotely monitored via the bioscatter signature. They also support prior speculation that some birds may seek the relatively laminar flow above an inversion base.

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de Macedo, Carina R., et José C. B. da Silva. « Internal Wave Dark-Band Signatures in ALOS-PALSAR Imagery Revealed by the Standard Deviation of the Co-Polarized Phase Difference ». Remote Sensing 12, n^o 15 (23 juillet 2020) : 2372. http://dx.doi.org/10.3390/rs12152372.

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Analysis of synthetic aperture radar (SAR) images in L-band of short-period internal waves (IWs), and classification of their radar signatures is presented by means of a polarimetric data set from ALOS-PALSAR mission. We choose the polarimetric feature named standard deviation(std) of the co-polarized phase difference (CPD) to identify fundamental differences in SAR signatures of internal waves, and divided them into three different classes, according to their backscattered modulation depths and morphology as well as the std CPD, namely: double-signed, single-negative, and single-positive signatures, for IW normalized image transects that display, respectively, signatures in the form of bright/dark, dark, and bright bands that correspond to positive/negative, negative, or positive variations of radar backscatter. These radar power types of signatures have a counterpart in the std CPD normalized transects, and in this paper we discuss those correlations and decorrelations. We focus in the single-negative type of signature, that is dark bands on gray background, and show that the std CPD is greatly enhanced over the troughs and rear slopes of those IWs. It is suggested that such behavior is consistent with the presence of surface slicks owing to enhanced surfactant concentration. Furthermore, those single-negative SAR signatures appear at locations where and when biological productivity is enhanced. It is found that the modulation depths associated to the std CPD is higher than the one associated to the HH-polarized radar backscatter for single-negative signatures propagating in the range direction, while the reverse occurs for the other types of signatures.

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Fors, Ane S., Dmitry V. Divine, Anthony P. Doulgeris, Angelika H. H. Renner et Sebastian Gerland. « Signature of Arctic first-year ice melt pond fraction in X-band SAR imagery ». Cryosphere 11, n^o 2 (23 mars 2017) : 755–71. http://dx.doi.org/10.5194/tc-11-755-2017.

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Abstract. In this paper we investigate the potential of melt pond fraction retrieval from X-band polarimetric synthetic aperture radar (SAR) on drifting first-year sea ice. Melt pond fractions retrieved from a helicopter-borne camera system were compared to polarimetric features extracted from four dual-polarimetric X-band SAR scenes, revealing significant relationships. The correlations were strongly dependent on wind speed and SAR incidence angle. Co-polarisation ratio was found to be the most promising SAR feature for melt pond fraction estimation at intermediate wind speeds (6. 2 m s−1), with a Spearman's correlation coefficient of 0. 46. At low wind speeds (0. 6 m s−1), this relation disappeared due to low backscatter from the melt ponds, and backscatter VV-polarisation intensity had the strongest relationship to melt pond fraction with a correlation coefficient of −0. 53. To further investigate these relations, regression fits were made both for the intermediate (R2fit = 0. 21) and low (R2fit = 0. 26) wind case, and the fits were tested on the satellite scenes in the study. The regression fits gave good estimates of mean melt pond fraction for the full satellite scenes, with less than 4 % from a similar statistics derived from analysis of low-altitude imagery captured during helicopter ice-survey flights in the study area. A smoothing window of 51 × 51 pixels gave the best reproduction of the width of the melt pond fraction distribution. A considerable part of the backscatter signal was below the noise floor at SAR incidence angles above ∼ 40°, restricting the information gain from polarimetric features above this threshold. Compared to previous studies in C-band, limitations concerning wind speed and noise floor set stricter constraints on melt pond fraction retrieval in X-band. Despite this, our findings suggest new possibilities in melt pond fraction estimation from X-band SAR, opening for expanded monitoring of melt ponds during melt season in the future.

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Shusse, Yukari, Nobuhiro Takahashi, Katsuhiro Nakagawa, Shinsuke Satoh et Toshio Iguchi. « Polarimetric Radar Observation of the Melting Layer in a Convective Rainfall System during the Rainy Season over the East China Sea ». Journal of Applied Meteorology and Climatology 50, n^o 2 (1 février 2011) : 354–67. http://dx.doi.org/10.1175/2010jamc2469.1.

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Abstract During the rainy season over the East China Sea, convective rainfalls often show melting layer (ML) characteristics in polarimetric radar variables. In this research, the appearance ratio of the ML (the ratio of rainfall area accompanied by polarimetric ML signatures) and the variation in height of the level of the ML signature maximum (MLSM level; defined by the level of the ρhv minimum in the ML) in a convective rainfall region in a rainfall system over the East China Sea observed on 2 June 2006 were studied using C-band polarimetric radar (COBRA). For this analysis, a method of rainfall type classification that evaluates the presence of an ML in addition to providing conventional convective–stratiform classification using range–height indicator (RHI) observation data was developed. This rainfall type classification includes two steps: conventional convective–stratiform separation using the horizontal distribution of Zh at 2-km altitude, and ML detection using the vertical profile of ρhv at each horizontal grid point. Using a combination of these two classifications, the following four rainfall types were identified: 1) convective rainfall with an ML, 2) convective rainfall with no ML, 3) stratiform rainfall with an ML, and 4) stratiform rainfall with no ML. An ML was detected in 53.9% of the convective region in the rainfall system. Using the same definition, an ML was detected in 83.1% of the stratiform region. The ML in the convective region showed a marked decrease in ρhv coincident with an increase in ZDR around the ambient 0°C level, as did that in the stratiform region. Melting aggregated snow was the likely cause of the ML signature in the convective region. The average height of the MLSM level in the convective region was 4.64 km, which is 0.46 km higher than that in the stratiform region (4.18 km) and 0.27 km higher than the ambient 0°C level (4.37 km).

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Johnson, Marcus, Youngsun Jung, Jason A. Milbrandt, Hugh Morrison et Ming Xue. « Effects of the Representation of Rimed Ice in Bulk Microphysics Schemes on Polarimetric Signatures ». Monthly Weather Review 147, n^o 10 (1 octobre 2019) : 3785–810. http://dx.doi.org/10.1175/mwr-d-18-0398.1.

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Abstract Many flavors of multicategory, multimoment bulk microphysics schemes (BMPs) have various treatments of rimed ice. In this study, we compare three two-moment schemes available in the WRF Model—Milbrandt–Yau (MY2), National Severe Storms Laboratory (NSSL), and the two-category configuration of the Predicted Particle Properties (P3) scheme—focusing on differences in rimed-ice representation and their impacts on surface rain and ice. Idealized supercell simulations are performed. A polarimetric radar data simulator is used to evaluate their ability to reproduce the ZDR arc and hail signature in the forward-flank downdraft, well-known supercell polarimetric signatures that are potentially sensitive to rimed-ice parameterization. Both the MY2 and NSSL schemes simulate enhanced surface ZDR bands, but neither scheme simulates a ZDR arc commonly identified in observation-based studies. Surface ZDR in the default P3 scheme is homogeneous in the supercell’s forward flank, and is due to the scheme’s restrictive minimum rain particle size distribution (PSD) slope bound preventing the presence of larger drops creating a ZDR arc. The NSSL scheme simulates the location of the hail signature in the forward-flank downdraft more consistent with observations than the other two schemes. Large hail in MY2 sediments well downstream of the updraft (atypically compared to observations) near the surface. The sedimentation of large ice in the default P3 scheme is limited by a restrictive maximum ice number-weighted mean diameter limit within the scheme, precluding the scheme’s ability to reduce ZDR (and ρHV compared to the MY2 and NSSL schemes) near the surface.

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Kuznetsov, V. A., et A. A. Potapov. « Texture-fractal analysis of polarimetric images generated by synthetic aperture radar stations. » Радиотехника и электроника 68, n^o 10 (1 octobre 2023) : 941–53. http://dx.doi.org/10.31857/s0033849423100145.

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All currently known methods and methods for the formation of fractalfeatures of polarimetric radar images. Briefly reviewed newtexture-fractal feature – a directional multifractal signature measured morphologically by the iterative covering method. In relation to the analysis of polarimetric images formed by a synthetic aperture radar, a new concept for their processing is proposed, based on the possibility of taking into account the polarization differences of ground-based spatially distributed objects by identifying the multifractal and anisotropic properties of their texture. A variant of interpretation of the obtained results for automatic optimization of further successful solution of specific segmentation (classification) problems underlying surface, detection and recognition of ground objects.

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Friedrich, Katja, Urs Germann et Pierre Tabary. « Influence of Ground Clutter Contamination on Polarimetric Radar Parameters ». Journal of Atmospheric and Oceanic Technology 26, n^o 2 (1 février 2009) : 251–69. http://dx.doi.org/10.1175/2008jtecha1092.1.

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Abstract The influence of ground clutter contamination on the estimation of polarimetric radar parameters, horizontal reflectivity (Zh), differential reflectivity (Zdr), correlation coefficient (ρhυ), and differential propagation phase (ϕdp) was examined. This study aims to derive the critical level of ground clutter contamination for Zh, Zdr, ρhυ, and ϕdp at which ground clutter influence exceeds predefined precision thresholds. Reference data with minimal ground clutter contamination consist of eight precipitation fields measured during three rain events characterized by stratiform and convective precipitation. Data were collected at an elevation angle of 0.8° by the Météo-France operational, polarimetric Doppler C-band weather radar located in Trappes, France, ∼30 km southwest of Paris. Nine different ground clutter signatures, ranging from point targets to more complex signatures typical for mountain ranges or urban obstacles, were added to the precipitation fields. This is done at the level of raw in-phase and quadrature component data in the two polarimetric channels. For each ground clutter signature, 30 simulations were conducted in which the mean reflectivity of ground clutter within the resolution volume varied between being 30 dB higher to 30 dB lower than the mean reflectivity of precipitation. Differences in Zh, Zdr, ρυ, and ϕdp between simulation and reference were shown as a function of ratio between ground clutter and precipitation intensities. As a result of this study, horizontal reflectivity showed the lowest sensitivity to ground clutter contamination. Furthermore, a precision of 1.7 dBZ in Zh is achieved on average when the precipitation and ground clutter intensities are equal. Requiring a precision of 0.2 dB in Zdr and 3° in ϕdp, the reflectivity of precipitation needs to be on average ∼5.5 and ∼6 dB, respectively, higher compared to the reflectivity of ground clutter. The analysis also indicates that the highest sensitivity to the nine clutter signatures was derived for ρhυ. To meet a predefined precision threshold of 0.02, reflectivity of precipitation needs to be ∼13.5 dB higher than the reflectivity of ground clutter.

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Hwang, Jehwan, Zahyun Ku, Jiyeon Jeon, Yeongho Kim, Deok-Kee Kim, Eun Kyu Kim et Sang Jun Lee. « Polarization-Sensitive and Wide Incidence Angle-Insensitive Fabry–Perot Optical Cavity Bounded by Two Metal Grating Layers ». Sensors 20, n^o 18 (20 septembre 2020) : 5382. http://dx.doi.org/10.3390/s20185382.

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Infrared (IR) polarimetric imaging has attracted attention as a promising technology in many fields. Generally, superpixels consisting of linear polarizer elements at different angles plus IR imaging array are used to obtain the polarized target signature by using the detected polarization-sensitive intensities. However, the spatial arrangement of superpixels across the imaging array may lead to an incorrect polarimetric signature of a target, due to the range of angles from which the incident radiation can be collected by the detector. In this article, we demonstrate the effect of the incident angle on the polarization performance of an alternative structure where a dielectric layer is inserted between the nanoimprinted subwavelength grating layers. The well-designed spacer creates the Fabry–Perot cavity resonance, and thereby, the intensity of transverse-magnetic I-polarized light transmitted through two metal grating layers is increased as compared with a single-layer metal grating, whereas transverse-electric (TE)-transmitted light intensity is decreased. TM-transmittance and polarization extinction ratio (PER) of normally incident light of wavelength 4.5 μm are obtained with 0.49 and 132, respectively, as the performance of the stacked subwavelength gratings. The relative change of the PERs for nanoimprint-lithographically fabricated double-layer grating samples that are less than 6% at an angle of incidence up to 25°, as compared to the normal incidence. Our work can pave the way for practical and efficient polarization-sensitive elements, which are useful for many IR polarimetric imaging applications.

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Kumjian, Matthew R., et Olivier P. Prat. « The Impact of Raindrop Collisional Processes on the Polarimetric Radar Variables ». Journal of the Atmospheric Sciences 71, n^o 8 (23 juillet 2014) : 3052–67. http://dx.doi.org/10.1175/jas-d-13-0357.1.

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Abstract The impact of the collisional warm-rain microphysical processes on the polarimetric radar variables is quantified using a coupled microphysics–electromagnetic scattering model. A one-dimensional bin-microphysical rain shaft model that resolves explicitly the evolution of the drop size distribution (DSD) under the influence of collisional coalescence and breakup, drop settling, and aerodynamic breakup is coupled with electromagnetic scattering calculations that simulate vertical profiles of the polarimetric radar variables: reflectivity factor at horizontal polarization ZH, differential reflectivity ZDR, and specific differential phase KDP. The polarimetric radar fingerprint of each individual microphysical process is quantified as a function of the shape of the initial DSD and for different values of nominal rainfall rate. Results indicate that individual microphysical processes (collisional processes, evaporation) display a distinctive signature and evolve within specific areas of ZH–ZDR and ZDR–KDP space. Furthermore, a comparison of the resulting simulated vertical profiles of the polarimetric variables with radar and disdrometer observations suggests that bin-microphysical parameterizations of drop breakup most frequently used are overly aggressive for the largest rainfall rates, resulting in very “tropical” DSDs heavily skewed toward smaller drops.

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Kubicke, Gildas, Christophe Bourlier et Joseph Saillard. « POLARIMETRIC BISTATIC SIGNATURE OF A FACETED OCTAHEDRON IN HIGH-FREQUENCY DOMAIN ». Progress In Electromagnetics Research 71 (2007) : 173–209. http://dx.doi.org/10.2528/pier07022801.

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Alouini, M., F. Goudail, N. Roux, L. Le Hors, P. Hartemann, S. Breugnot et D. Dolfi. « Active spectro-polarimetric imaging : signature modeling, imaging demonstrator and target detection ». European Physical Journal Applied Physics 42, n^o 2 (28 mars 2008) : 129–39. http://dx.doi.org/10.1051/epjap:2008034.

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