The Experts below are selected from a list of 10278 Experts worldwide ranked by ideXlab platform
Haimin Wang - One of the best experts on this subject based on the ideXlab platform.
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transient rotation of photospheric vector magnetic fields associated with a solar flare
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Wenda Cao, Kwangsu Ahn, Ju Jing, Chang Liu, Jongchul Chae, Nengyi Huang, Na Deng, Dale E Gary, Haimin WangAbstract:As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6-m Goode Solar Telescope, here we show a sudden rotation of vector magnetic fields, about 12$^{\circ}$-20$^{\circ}$ counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the Azimuth-Angle change is transient and co-spatial/temporal with H$\alpha$ emission. The measured Azimuth Angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56~$\mu$m, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high energy electron beams or $Alfv\acute{e}n$ waves play a crucial role.
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transient rotation of photospheric vector magnetic fields associated with a solar flare
Nature Communications, 2018Co-Authors: Wenda Cao, Kwangsu Ahn, Ju Jing, Chang Liu, Jongchul Chae, Nengyi Huang, Na Deng, Dale E Gary, Haimin WangAbstract:As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer, and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6 m Goode Solar Telescope, here, we show a sudden rotation of vector magnetic fields, about 12–20° counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the Azimuth-Angle change is transient and cospatial/temporal with Hα emission. The measured Azimuth Angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56 μm, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high-energy electron beams or Alfve′n waves play a crucial role. The violent solar eruptions known as flares are caused by magnetic reconnection. Here, the authors identify a sudden 12°–20° counter clockwise rotation of vector magnetic fields in photosphere, associated with the emissions of moving flare ribbons.
Junichi Susaki - One of the best experts on this subject based on the ideXlab platform.
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urban density estimation from polarimetric sar images based on a poa correction method
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2013Co-Authors: Muneyoshi Kajimoto, Junichi SusakiAbstract:In this paper, an algorithm for estimating urban density from polarimetric synthetic aperture radar (SAR) images is proposed. Polarization orientation Angle (POA) and four power components derived by four-component decomposition are used in the algorithm. In particular, in urban areas, SAR data are generally affected by factors such as the interval between buildings, building height, and building Azimuth Angle. Here, building Azimuth (orientation) Angle means the relative Azimuth between the wall normal and the radar's ground range direction. The interval between buildings and building height are used for building density calculation such as the building-to-land ratio and the floor area ratio. However, building Azimuth Angle which depends on satellite orbit has almost no relation with building density. The scattering intensity of microwaves emitted from SAR has a strong dependence on this building Azimuth Angle. Therefore, the main part of this paper is focused on the correction of this angular effect. The first step in the POA correction method is the extraction of homogeneous-POA city districts. In the second step, each power component's scattering intensity is normalized for all pixels in a particular POA interval separately for different POA types of districts. In the case of Tokyo metropolitan area, Japan, estimated urban density from ALOS/PALSAR data has correlation coefficients of nearly 0.7 with the building-to-land ratio and 0.5 with the floor area ratio on the scale of hundreds of meter. In the areas where strong POA dependence is seen, the improvement of the correlation coefficient runs up to approximately 0.2.
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classification of building area using Azimuth Angle and density indices derived from polarimetric sar
Urban Remote Sensing Joint Event, 2011Co-Authors: Shogo Iwasa, Junichi SusakiAbstract:Urban extraction is one of the most anticipated applications of remote sensing, but automatic extraction has been challenging. Synthetic aperture radar (SAR) applications are particularly problematic because the scattering in urban areas is sensitive to the spatial arrangement of buildings, which prevents extraction. Spaceborne polarimetric synthetic aperture radar (POLSAR), an advanced approach to SAR, has been available since ALOS/PALSAR was launched in 2006. Several indicators derived from POLSAR data have been developed to classify land cover, and some of them have been utilized to extract the geometric features of a target. So, as a first step, we measured the backscattering from concrete blocks arranged with different Azimuth Angles and distances in an anechoic radio wave chamber. Through this experiment, we found the interrelation between spatial arrangement and various polarimetric indices, and demonstrated that Polarization Orientation Angle (POA) is a good detector for the Azimuth Angle of man-made structures. We also found that entropy has the highest correlation with building density. Then we classified urban areas in satellite polarimetric data using POA and entropy. A comparison with Quickbird image indicated that POA is an effective indicator to extract non-perpendicular buildings and that there are some areas where entropy distinguishes differences in building density.
Anbang Zhao - One of the best experts on this subject based on the ideXlab platform.
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open lake experimental investigation of Azimuth Angle estimation using a single acoustic vector sensor
Journal of Sensors, 2018Co-Authors: Anbang Zhao, Juan Hui, Caigao ZengAbstract:Five well-known Azimuth Angle estimation methods using a single acoustic vector sensor (AVS) are investigated in open-lake experiments. A single AVS can measure both the acoustic pressure and acoustic particle velocity at a signal point in space and output multichannel signals. The Azimuth Angle of one source can be estimated by using a single AVS in a passive sonar system. Open-lake experiments are carried out to evaluate how these different techniques perform in estimating Azimuth Angle of a source. The AVS that was applied in these open-lake experiments is a two-dimensional accelerometer structure sensor. It consists of two identical uniaxial velocity sensors in orthogonal orientations, plus a pressure sensor—all in spatial collocation. These experimental results indicate that all these methods can effectively realize the Azimuth Angle estimation using only one AVS. The results presented in this paper reveal that AVS can be applied in a wider range of application in distributed underwater acoustic systems for passive detection, localization, classification, and so on.
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an improved Azimuth Angle estimation method with a single acoustic vector sensor based on an active sonar detection system
Sensors, 2017Co-Authors: Anbang ZhaoAbstract:In this paper, an improved Azimuth Angle estimation method with a single acoustic vector sensor (AVS) is proposed based on matched filtering theory. The proposed method is mainly applied in an active sonar detection system. According to the conventional passive method based on complex acoustic intensity measurement, the mathematical and physical model of this proposed method is described in detail. The computer simulation and lake experiments results indicate that this method can realize the Azimuth Angle estimation with high precision by using only a single AVS. Compared with the conventional method, the proposed method achieves better estimation performance. Moreover, the proposed method does not require complex operations in frequencydomain and achieves computational complexity reduction.
Wenda Cao - One of the best experts on this subject based on the ideXlab platform.
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transient rotation of photospheric vector magnetic fields associated with a solar flare
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Wenda Cao, Kwangsu Ahn, Ju Jing, Chang Liu, Jongchul Chae, Nengyi Huang, Na Deng, Dale E Gary, Haimin WangAbstract:As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6-m Goode Solar Telescope, here we show a sudden rotation of vector magnetic fields, about 12$^{\circ}$-20$^{\circ}$ counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the Azimuth-Angle change is transient and co-spatial/temporal with H$\alpha$ emission. The measured Azimuth Angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56~$\mu$m, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high energy electron beams or $Alfv\acute{e}n$ waves play a crucial role.
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transient rotation of photospheric vector magnetic fields associated with a solar flare
Nature Communications, 2018Co-Authors: Wenda Cao, Kwangsu Ahn, Ju Jing, Chang Liu, Jongchul Chae, Nengyi Huang, Na Deng, Dale E Gary, Haimin WangAbstract:As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer, and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6 m Goode Solar Telescope, here, we show a sudden rotation of vector magnetic fields, about 12–20° counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the Azimuth-Angle change is transient and cospatial/temporal with Hα emission. The measured Azimuth Angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56 μm, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high-energy electron beams or Alfve′n waves play a crucial role. The violent solar eruptions known as flares are caused by magnetic reconnection. Here, the authors identify a sudden 12°–20° counter clockwise rotation of vector magnetic fields in photosphere, associated with the emissions of moving flare ribbons.
Ju Jing - One of the best experts on this subject based on the ideXlab platform.
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transient rotation of photospheric vector magnetic fields associated with a solar flare
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: Wenda Cao, Kwangsu Ahn, Ju Jing, Chang Liu, Jongchul Chae, Nengyi Huang, Na Deng, Dale E Gary, Haimin WangAbstract:As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6-m Goode Solar Telescope, here we show a sudden rotation of vector magnetic fields, about 12$^{\circ}$-20$^{\circ}$ counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the Azimuth-Angle change is transient and co-spatial/temporal with H$\alpha$ emission. The measured Azimuth Angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56~$\mu$m, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high energy electron beams or $Alfv\acute{e}n$ waves play a crucial role.
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transient rotation of photospheric vector magnetic fields associated with a solar flare
Nature Communications, 2018Co-Authors: Wenda Cao, Kwangsu Ahn, Ju Jing, Chang Liu, Jongchul Chae, Nengyi Huang, Na Deng, Dale E Gary, Haimin WangAbstract:As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer, and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6 m Goode Solar Telescope, here, we show a sudden rotation of vector magnetic fields, about 12–20° counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the Azimuth-Angle change is transient and cospatial/temporal with Hα emission. The measured Azimuth Angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56 μm, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high-energy electron beams or Alfve′n waves play a crucial role. The violent solar eruptions known as flares are caused by magnetic reconnection. Here, the authors identify a sudden 12°–20° counter clockwise rotation of vector magnetic fields in photosphere, associated with the emissions of moving flare ribbons.
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Transient rotation of photospheric vector magnetic fields associated with a solar flare
'Springer Science and Business Media LLC', 2018Co-Authors: Xu Yan, Ju Jing, Na Deng, Cao Wenda, Ahn Kwangsu, Liu Chang, Chae Jongchul, Huang Nengyi, Gary, Dale E., Wang HaiminAbstract:As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6-m Goode Solar Telescope, here we show a sudden rotation of vector magnetic fields, about 12$^{\circ}$-20$^{\circ}$ counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the Azimuth-Angle change is transient and co-spatial/temporal with H$\alpha$ emission. The measured Azimuth Angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56~$\mu$m, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high energy electron beams or $Alfv\acute{e}n$ waves play a crucial role.Comment: http://rdcu.be/Epb
