The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform
Jenn-shyong Chen - One of the best experts on this subject based on the ideXlab platform.
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A Novel Approach to Mitigation of Radar Beam Weighting Effect on Coherent Radar Imaging Using VHF Atmospheric Radar
IEEE Transactions on Geoscience and Remote Sensing, 2011Co-Authors: Jenn-shyong Chen, Jun-ichi FurumotoAbstract:Multiple-receiver coherent Radar imaging using very high frequency atmospheric Radars is capable of imaging angular power distribution (termed brightness distribution) of the backscattered Radar echoes with some inversion algorithms such as Capon's method. The brightness distribution, however, is weighted by the Radar beam weighting pattern. Modification of the brightness distribution with a simulated Radar beam weighting pattern usually incurs spurious peaks around the edge of the distribution map. In view of this, an approach to mitigation of the Radar beam weighting effect on brightness distribution is proposed, thereby giving more reliable estimates of echo center and brightness width. The proposed approach employs several pairs of symmetrically tilted Radar Beams to determine an effective weighting pattern of the Radar beam that is adaptive to the signal-to-noise ratio (SNR) of the data, as well as the transmitting-receiving array configuration. Four Radar experiments were carried out with the Middle and Upper atmosphere Radar in Japan (34.85°N , 136.11°E) to demonstrate the proposed approach. One of the experiments was exhibited in more detail, and it showed the following: 1) Approximately 14% of the single-center cases turned into double-center situations; 2) the zenith angles of the corrected echo centers were larger than the original ones by ~0.75° on average; and 3) the brightness widths could be larger than the original ones by several degrees, depending on the SNR of the data. Based on these investigations, suitable corrections of the echo center and brightness width are expected to result in different estimates of some atmospheric parameters like scatterer anisotropy and tilt angle of the layer structure.
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Effects of Radar beam width and scatterer anisotropy on multiple-frequency range imaging using VHF atmospheric Radar
Radio Science, 2010Co-Authors: Jenn-shyong Chen, Jun-ichi Furumoto, Takuji NakamuraAbstract:[1] Benefiting from the changeable antenna array size and flexible Radar beam direction of the middle and upper (MU) atmosphere Radar (34.85°N, 136.11°E), the effects of Radar beam width and scatterer anisotropy on the performance of multiple-frequency range imaging (RIM) were examined in addition to numerical simulation. First, nine transmitter/receiver modes were employed to reveal that a wider Radar beam gives a larger phase bias in the RIM processing. Based on this, layer positions and layer thicknesses were estimated from the imaged powers of various Radar beam widths after corrections of phase bias and range-weighting function effect. Statistical examination showed that the imaged layer structure was thicker for a larger Radar beam width and this feature became more evident at a higher altitude, thereby demonstrating the influence of Radar beam width on the practical performance of RIM. Second, the scatterer anisotropy in the layer structure was examined by means of a vertical and three oblique Radar Beams (5°, 10°, and 15° north), which were transmitted in company with the RIM technique. The vertical beam observed some single-layer and double-layer structures that were not always detected by the oblique Beams, indicating the existence of anisotropic scatterers in the layers. In addition, a comparison of layer positions between the vertical and oblique Radar Beams showed that anisotropic characteristics of the upper and lower layers of a double-layer structure can be different, demonstrating one more capability of RIM for investigating fine-scale features of the atmospheric layer structures.
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Coherent Radar imaging of mesosphere summer echoes: Influence of Radar beam pattern and tilted structures on atmospheric echo center
Radio Science, 2008Co-Authors: Jenn-shyong Chen, Peter Hoffmann, Marius Zecha, Cheng-hsiung HsiehAbstract:[1] Multiple echo centers of a mesosphere-summer-echo layer (MSE) observed by the six-receiver OSWIN VHF Radar (54.1°N, 11.8°E) were examined with the coherent Radar imaging (CRI) technique. The data were collected by different observational modes: vertical and oblique Radar Beams with the receiving configurations of 3 × 2, 6 × 1 (meridional alignment) and 1 × 6 (zonal alignment) antenna groups. The unique receiving configurations of meridional and zonal aligned antenna groups reveal that the echo centers clustered in three distinct groups above the range height of ∼86 km. The central group of echo centers was around the direction of Radar beam; however, the off-zenith angles of the two side groups, ranging between several and 20 degrees, increased with ascendant range height. Two potential causes of the echoes in the two side groups were examined on the basis of simulation calculation, namely, tilted structures in the layer and additionally, the influence of Radar beam pattern. It is indicated that some echoes, originating from the lower part ( ∼86 km) at larger off-zenith angles. The tilted structures, which are considered to be related to wave activities, can also produce the features similar to the observations. This is demonstrated by simulation calculation with wavy reflecting layers, in which the waves are supposed to modulate the multiple reflecting layers, with increasing amplitudes, tilted shapes, asynchronous phases, and horizontal travel.
C. L. Fern - One of the best experts on this subject based on the ideXlab platform.
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Phase and group velocity tracing analysis of projected wave packet motion along oblique Radar Beams – qualitative analysis of QP echoes
Annales Geophysicae, 2007Co-Authors: F. S. Kuo, H. Y. Lue, C. L. FernAbstract:Abstract. The wave packets of atmospheric gravity waves were numerically generated, with a given characteristic wave period, horizontal wave length and projection mean wind along the horizontal wave vector. Their projection phase and group velocities along the oblique Radar beam ( v pr and v gr ), with different zenith angle θ and azimuth angle φ, were analyzed by the method of phase- and group-velocity tracing. The results were consistent with the theoretical calculations derived by the dispersion relation, reconfirming the accuracy of the method of analysis. The RTI plot of the numerical wave packets were similar to the striation patterns of the QP echoes from the FAI irregularity region. We propose that the striation range rate of the QP echo is equal to the radial phase velocity v pr , and the slope of the energy line across the neighboring striations is equal to the radial group velocity v gr of the wave packet; the horizontal distance between two neighboring striations is equal to the characteristic wave period τ. Then, one can inversely calculate all the properties of the gravity wave responsible for the appearance of the QP echoes. We found that the possibility of some QP echoes being generated by the gravity waves originated from lower altitudes cannot be ruled out.
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phase and group velocity tracing analysis of projected wave packet motion along oblique Radar Beams qualitative analysis of qp echoes
Annales Geophysicae, 2007Co-Authors: F. S. Kuo, H. Y. Lue, C. L. FernAbstract:Abstract. The wave packets of atmospheric gravity waves were numerically generated, with a given characteristic wave period, horizontal wave length and projection mean wind along the horizontal wave vector. Their projection phase and group velocities along the oblique Radar beam ( v pr and v gr ), with different zenith angle θ and azimuth angle φ, were analyzed by the method of phase- and group-velocity tracing. The results were consistent with the theoretical calculations derived by the dispersion relation, reconfirming the accuracy of the method of analysis. The RTI plot of the numerical wave packets were similar to the striation patterns of the QP echoes from the FAI irregularity region. We propose that the striation range rate of the QP echo is equal to the radial phase velocity v pr , and the slope of the energy line across the neighboring striations is equal to the radial group velocity v gr of the wave packet; the horizontal distance between two neighboring striations is equal to the characteristic wave period τ. Then, one can inversely calculate all the properties of the gravity wave responsible for the appearance of the QP echoes. We found that the possibility of some QP echoes being generated by the gravity waves originated from lower altitudes cannot be ruled out.
Jun-ichi Furumoto - One of the best experts on this subject based on the ideXlab platform.
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A Novel Approach to Mitigation of Radar Beam Weighting Effect on Coherent Radar Imaging Using VHF Atmospheric Radar
IEEE Transactions on Geoscience and Remote Sensing, 2011Co-Authors: Jenn-shyong Chen, Jun-ichi FurumotoAbstract:Multiple-receiver coherent Radar imaging using very high frequency atmospheric Radars is capable of imaging angular power distribution (termed brightness distribution) of the backscattered Radar echoes with some inversion algorithms such as Capon's method. The brightness distribution, however, is weighted by the Radar beam weighting pattern. Modification of the brightness distribution with a simulated Radar beam weighting pattern usually incurs spurious peaks around the edge of the distribution map. In view of this, an approach to mitigation of the Radar beam weighting effect on brightness distribution is proposed, thereby giving more reliable estimates of echo center and brightness width. The proposed approach employs several pairs of symmetrically tilted Radar Beams to determine an effective weighting pattern of the Radar beam that is adaptive to the signal-to-noise ratio (SNR) of the data, as well as the transmitting-receiving array configuration. Four Radar experiments were carried out with the Middle and Upper atmosphere Radar in Japan (34.85°N , 136.11°E) to demonstrate the proposed approach. One of the experiments was exhibited in more detail, and it showed the following: 1) Approximately 14% of the single-center cases turned into double-center situations; 2) the zenith angles of the corrected echo centers were larger than the original ones by ~0.75° on average; and 3) the brightness widths could be larger than the original ones by several degrees, depending on the SNR of the data. Based on these investigations, suitable corrections of the echo center and brightness width are expected to result in different estimates of some atmospheric parameters like scatterer anisotropy and tilt angle of the layer structure.
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Effects of Radar beam width and scatterer anisotropy on multiple-frequency range imaging using VHF atmospheric Radar
Radio Science, 2010Co-Authors: Jenn-shyong Chen, Jun-ichi Furumoto, Takuji NakamuraAbstract:[1] Benefiting from the changeable antenna array size and flexible Radar beam direction of the middle and upper (MU) atmosphere Radar (34.85°N, 136.11°E), the effects of Radar beam width and scatterer anisotropy on the performance of multiple-frequency range imaging (RIM) were examined in addition to numerical simulation. First, nine transmitter/receiver modes were employed to reveal that a wider Radar beam gives a larger phase bias in the RIM processing. Based on this, layer positions and layer thicknesses were estimated from the imaged powers of various Radar beam widths after corrections of phase bias and range-weighting function effect. Statistical examination showed that the imaged layer structure was thicker for a larger Radar beam width and this feature became more evident at a higher altitude, thereby demonstrating the influence of Radar beam width on the practical performance of RIM. Second, the scatterer anisotropy in the layer structure was examined by means of a vertical and three oblique Radar Beams (5°, 10°, and 15° north), which were transmitted in company with the RIM technique. The vertical beam observed some single-layer and double-layer structures that were not always detected by the oblique Beams, indicating the existence of anisotropic scatterers in the layers. In addition, a comparison of layer positions between the vertical and oblique Radar Beams showed that anisotropic characteristics of the upper and lower layers of a double-layer structure can be different, demonstrating one more capability of RIM for investigating fine-scale features of the atmospheric layer structures.
Vladimir Badin - One of the best experts on this subject based on the ideXlab platform.
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Resonant ULF Absorption Revealed by Auroral Doppler Radar Data
Geomagnetism and Aeronomy, 2019Co-Authors: Vladimir BadinAbstract:STARE Doppler data on electron drift velocities detected in the auroral ionosphere for weakly disturbed conditions are analyzed. The Doppler measurements are first averaged along each Radar beam. The power spectral density (PSD) as a function of frequency is then calculated by discrete Fourier transforms of averaged signals for every Radar beam. Deep stepwise drops (about 10 dB) in spectral powers of the ultra-low-frequency (ULF) range are revealed for all Radar Beams. These PSD drops are interpreted as manifestations of resonant ULF absorption, which occurs in the eigenfrequency continuum of standing Alfven waves excited on geomagnetic field lines. A variational analysis that models PSD decreases by stepwise profiles of the mean spectral powers is proposed. This analysis provides the least-squares fitting of model profiles to PSD decreases calculated by the data. The frequency of the mean PSD step determined for each Radar beam is treated as the minimum frequency of resonant ULF absorption revealed by this beam during the given auroral event. Averaged over all Beams, this frequency for the analyzed event is 4.9 ± 0.2 mHz.
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Resonant ULF absorption at storm time conditions
Solnechno-Zemnaya Fizika, 2017Co-Authors: Владимир Бадин, Vladimir BadinAbstract:The work deals with ULF Radar observations of the high-latitude ionosphere. Doppler data from the Norwegian STARE instrument are analyzed for the moderate magnetic storm observed on December 31, 1999–January 01, 2000. Upon averaging the Doppler signals along Radar Beams, the spectral power of signals is determined for each beam as a function of frequency ranging from 1 to 10 mHz. Sharp drops (about 10 dB) of spectral powers with frequency are found for all Radar Beams. A variational analysis of spectral powers is carried out by least squares, with power drops being modeled by stepwise profiles constructed of mean spectral powers preceding and succeeding the drops. Using this variational analysis, the frequency of the power drop is determined for each Radar beam. Being averaged over all Beams, this frequency is 4.8±0.5 mHz. The results obtained are interpreted as resonant absorption of ultra-low-frequency (ULF) waves occurring on eigenfrequencies of magnetic field lines over wave propagation from the magnetopause deep into the magnetosphere.
F. S. Kuo - One of the best experts on this subject based on the ideXlab platform.
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Phase and group velocity tracing analysis of projected wave packet motion along oblique Radar Beams – qualitative analysis of QP echoes
Annales Geophysicae, 2007Co-Authors: F. S. Kuo, H. Y. Lue, C. L. FernAbstract:Abstract. The wave packets of atmospheric gravity waves were numerically generated, with a given characteristic wave period, horizontal wave length and projection mean wind along the horizontal wave vector. Their projection phase and group velocities along the oblique Radar beam ( v pr and v gr ), with different zenith angle θ and azimuth angle φ, were analyzed by the method of phase- and group-velocity tracing. The results were consistent with the theoretical calculations derived by the dispersion relation, reconfirming the accuracy of the method of analysis. The RTI plot of the numerical wave packets were similar to the striation patterns of the QP echoes from the FAI irregularity region. We propose that the striation range rate of the QP echo is equal to the radial phase velocity v pr , and the slope of the energy line across the neighboring striations is equal to the radial group velocity v gr of the wave packet; the horizontal distance between two neighboring striations is equal to the characteristic wave period τ. Then, one can inversely calculate all the properties of the gravity wave responsible for the appearance of the QP echoes. We found that the possibility of some QP echoes being generated by the gravity waves originated from lower altitudes cannot be ruled out.
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phase and group velocity tracing analysis of projected wave packet motion along oblique Radar Beams qualitative analysis of qp echoes
Annales Geophysicae, 2007Co-Authors: F. S. Kuo, H. Y. Lue, C. L. FernAbstract:Abstract. The wave packets of atmospheric gravity waves were numerically generated, with a given characteristic wave period, horizontal wave length and projection mean wind along the horizontal wave vector. Their projection phase and group velocities along the oblique Radar beam ( v pr and v gr ), with different zenith angle θ and azimuth angle φ, were analyzed by the method of phase- and group-velocity tracing. The results were consistent with the theoretical calculations derived by the dispersion relation, reconfirming the accuracy of the method of analysis. The RTI plot of the numerical wave packets were similar to the striation patterns of the QP echoes from the FAI irregularity region. We propose that the striation range rate of the QP echo is equal to the radial phase velocity v pr , and the slope of the energy line across the neighboring striations is equal to the radial group velocity v gr of the wave packet; the horizontal distance between two neighboring striations is equal to the characteristic wave period τ. Then, one can inversely calculate all the properties of the gravity wave responsible for the appearance of the QP echoes. We found that the possibility of some QP echoes being generated by the gravity waves originated from lower altitudes cannot be ruled out.
