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  • 2010-2014  (490)
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  • 1
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    Buried Object Detection by Means of a Lp Banach-Space Inversion Procedure (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-18
    Description: Electromagnetic inspection techniques are becoming powerful tools for buried object detection and subsurface prospection in several applicative fields, such as civil engineering and archeology. However, the nonlinearity and ill-posedness of the underlying inverse problem make the development of efficient imaging techniques a very challenging task. In the present paper, an algorithm based on a regularizing approach in L p Banach spaces is proposed for tackling such problems. The effectiveness of the approach is verified by means of numerical simulations in a noisy environment, aimed at evaluating the reconstruction capabilities with respect to the choice of several model parameters. The reported results show that, for small targets, the use of L p Banach spaces with 1 〈  p  〈 2 allows to obtain a better localization of different buried scatterers.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 2
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    Coherent Time Reversal Microwave Imaging for the Detection and Localization of Breast Tissue Malignancies (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-16
    Description: This paper deals with coherent processing of time reversal operator for microwave imaging in the frequency-domain. In frequency-domain time-reversal imaging approach, images obtained for different frequency bins over ultrawideband are incoherently processed. In highly dense and cluttered medium the signal subspace over each narrow frequency bin varies from that obtained using the complete ultrawideband. As a result, the detection and localization from non-coherent imaging approach is often inconclusive. In order to improve the stability of time-reversal microwave imaging, we propose coherent processing using novel focusing matrix approach. The proposed focusing matrix makes possible the time-reversal imaging technique to coherently process each frequency bin to yield a consistent signal subspace. The performance of coherent focusing is investigated when combined with time-reversal robust capon beamformer (TR-RCB). We have used numerical experiments on breast cancer detection using FDTD employing anatomically realistic numerical breast phantoms that contain varying amounts of dense fibro-glandular tissue content. The imaging results indicate that the proposed Coherent-TR-RCB (C-TR-RCB) could overcome the limitations of time-reversal imaging in a highly heterogeneous and cluttered medium.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 3
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    Design and Numerical Verification of Plasmonic Cross Antennas to Generate Localized Circularly Polarized Light for All-Optical Magnetic Recording (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-16
    Description: All-optical magnetic recording with localized circularly polarized light is studied for realizing ultra-fast and high-density magnetic recording. We design plasmonic cross antennas with bit-patterned media and evaluate the Stokes parameters. Using our proposed method, the magnetic recording speed is about 100,000 times faster than that for conventional methods and the recording density becomes over 2Tbit/inch 2 .
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    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 4
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    Understanding Instrumental Stokes Leakage in Murchison Widefield Array Polarimetry (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-14
    Description: This paper offers an electromagnetic, more specifically array theory, perspective on understanding strong instrumental polarization effects for planar low-frequency “aperture arrays” with the Murchison Widefield Array (MWA) as an example. A long-standing issue that has been seen here is significant instrumental Stokes leakage after calibration, particularly in Stokes Q at high frequencies. A simple model that accounts for inter-element mutual coupling is presented which explains the prominence of Q leakage seen when the array is scanned away from zenith in the principal planes. On these planes, the model predicts current imbalance in the X (E-W) and Y (N-S) dipoles and hence the Q leakage. Although helpful in concept, we find that this model is inadequate to explain the full details of the observation data. This finding motivates further experimentation with more rigorous models that account for both mutual coupling and embedded element patterns. Two more rigorous models are discussed: the “full” and “average” embedded element patterns. The viability of the “full” model is demonstrated by simulating current MWA practice of using a Hertzian dipole model as a Jones matrix estimate. We find that these results replicate the observed Qleakage to approximately 2 to 5%. Finally, we offer more direct indication for the level of improvement expected from upgrading the Jones matrix estimate with more rigorous models. Using the “average” embedded pattern as an estimate for the “full” model, we find that Q leakage of a few percent is achievable.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 5
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    Extremely Low Frequency Band Station for Natural Electromagnetic Noise Measurement (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-14
    Description: A new permanent ELF measurement station has been deployed in Sierra Nevada, Spain. It is composed of two magnetometers, oriented NS and EW, respectively. At 10 Hz, their sensitivity is 19 μ zV/pT and the Signal to Noise Ratio (SNR) is 28 dB for a time-varying signal of 1 pT, the expected field amplitude in Sierra Nevada. The station operates for frequencies below 24 Hz. The magnetometers, together with their corresponding electronics, have been specifically designed to achieve such an SNR for small signals. They are based on high-resolution search coils with ferromagnetic core and 10 6 turns, operating in limited geometry configuration. Different system noise sources are considered and a study of the SNR is also included. Finally, some initial Schumann resonance measurements are presented in order to validate the performance of the measurement station, including one hour length spectra, daily variations of resonance amplitudes and frequencies for the different seasons, and a three day spectrogram.
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    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 6
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    Anomalous Absorption, Plasmonic Resonances, and Invisibility of Radially Anisotropic Spheres (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-14
    Description: This article analyzes the response of a sphere with radially anisotropic permittivity dyadic (RA sphere), in both the electrostatic and full electrodynamic settings. Depending on the values and signs of the permittivity components, the quasistatic polarizability of the RA sphere exhibits several very different interesting properties, including invisibility, field concentration, resonant singularities, and emergent losses. Special attention is given to the anomalous losses that appear in the case of certain hyperbolic anisotropy values. We show that their validity can be justified in a limiting sense by puncturing the sphere at the origin and adding a small imaginary part into the permittivity components. A hyperbolic RA sphere with very small intrinsic losses can thus have significant effective losses making it an effective absorber. With different choice of permittivities, the RA sphere could also perform as a cloak or a sensor. The Mie scattering results by an RA sphere are used to justify the quasistatic calculations. It is shown that in the small parameter limit the absorption efficiency of an RA sphere is non-zero for certain lossless hyperbolic anisotropies. The absorption and scattering efficiencies agree with the quasistatic calculations fairly well for spheres with size parameters up to 1/3.
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    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 7
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    Issue Information (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-13
    Description: No abstract is available for this article.
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    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 8
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    Rice Growth Monitoring using Simulated Compact Polarimetric C-band SAR (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-06
    Description: In this study, a set of nine compact polarimetric (CP) images were simulated from polarimetric RADARSAT-2 data acquired over a test site containing two types of rice field in Jiangsu province, China. The types of rice field in the test site were (1) transplanted hybrid rice fields, and (2) direct-sown japonica rice fields. Both types have different yields and phenological stages. As a first step, the two types of rice field were distinguished with 94% and 86% accuracy respectively through analyzing CP SAR observations and their behavior in terms of scattering mechanisms during the rice growth season. The focus was then on phenology retrieval for each type of rice field. A decision tree (DT) algorithm was built to fulfill the precise retrieval of rice phenological stages, in which seven phenological stages were discriminated. The key criterion for each phenological stage was composed of 1–4 CP parameters, some of which were firstly used for rice phenology retrieval and found to be very sensitive to rice phenological changes. The retrieval results were verified at parcel level for a set of 12 stands of rice and up to nine observation dates per stand. This gave an accuracy of 88-95%. Throughout the phenology retrieval process, only simulated CP data was used, without any auxiliary data. These results demonstrate the potential of CP SAR for rice growth monitoring applications.
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    Topics: Geosciences , Physics
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  • 9
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    Observed high-latitude GNSS disturbances during a less-than-minor geomagnetic storm (2014)
    Wiley-Blackwell
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    Publication Date: 2014-12-03
    Description: This paper presents the effects of a weak geomagnetic storm event on January 17, 2013. While the Kp index reached a maximum of only 4, this event still caused severe disturbances for GNSS-based positioning services at high latitudes. We present data from the Norwegian Mapping Authority's Real Time Ionospheric Monitor (RTIM), based on a dense network of geodetic receivers, and scintillation indices from scintillation receivers located in Norway. In northern parts of Norway, the Centimeter positioning service (CPOS) was severely disturbed for hours. Service monitoring measurements showed that the effect was significantly worse for a receiver far away from the nearest network reference station.
    Print ISSN: 0048-6604
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    Topics: Geosciences , Physics
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  • 10
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    Boundary conditions for electric quadrupolar continua (2014)
    Wiley-Blackwell
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    Publication Date: 2014-11-27
    Description: After defining a continuum using rigorous spatial-dispersion equations for the macroscopic, fundamental Floquet modal fields of 3D periodic metamaterial arrays, boundary conditions are derived for electric quadrupolar continua under the assumption that the electric quadrupolarization density contains no extra delta functions within the interface transition layer (in addition to the delta function that usually occurs in the divergence of the electric quadrupolarization across the interface). A physically reasonable constitutive relation, in which the electric quadrupolarization density is proportional to the spatial derivatives of the electric field, is used to examine this assumption and the applicability of the boundary conditions. It is found that, although extra delta functions can be produced by a TM plane wave incident upon an interface, the boundary conditions remain essentially unaffected by these extra delta functions for small enough electrical separation distances between the inclusions of the arrays.
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    Topics: Geosciences , Physics
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