The Experts below are selected from a list of 3213 Experts worldwide ranked by ideXlab platform
Jun A Zhang - One of the best experts on this subject based on the ideXlab platform.
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Identification of Tropical Cyclone Centers in SAR Imagery Based on Template Matching and Particle Swarm Optimization Algorithms
IEEE Transactions on Geoscience and Remote Sensing, 2019Co-Authors: Shaohui Jin, Jun A Zhang, Xiaofeng Yang, Dongliang ShenAbstract:Synthetic aperture radar (SAR) has emerged as a new tool for tropical cyclone (TC) monitoring by providing information on the location of TC centers. However, SAR does not usually cover the entire TC domain due to its limited swath width. In this paper, we develop a procedure to identify the location of the center of a TC when an SAR image only covers the rain band portion of the TC but not the eye. The algorithm is based on both an image processing procedure and the available knowledge of the inherent rain-band structure of a TC. The three-step algorithm includes: 1) applying a Canny edge detector to find the curves associated with rain bands; 2) defining two filter criteria to select the spiral curves that resemble the estimation based on a TC rain-band model; 3) searching for the optimal matching solution using the particle swarm optimization algorithm. Numerical experiments with images without TC eye information show that the proposed method can effectively locate the centers of TCs. We compare the experimental results with the best track data to indicate the accuracy. Then, we compare the Inflow Angle model and the logarithmic spiral model and find that the Inflow Angle model is more accurate for TC center identification.
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A Hurricane Morphology and Sea Surface Wind Vector Estimation Model Based on C-Band Cross-Polarization SAR Imagery
IEEE Transactions on Geoscience and Remote Sensing, 2017Co-Authors: Guosheng Zhang, William Perrie, Xiaofeng Li, Jun A ZhangAbstract:Over the last decades, data from spaceborne synthetic aperture radar (SAR) have been used in hurricane research. However, some issues remain. When wind is at hurricane strength, the wind speed retrievals from single-polarization SAR may have errors, because the backscatter signal may experience saturation and become double valued. By comparison, wind direction retrievals from cross-polarization SAR are not possible until now. In this paper, we develop a 2-D model, the symmetric hurricane estimates for wind (SHEW) model, and combine it with the modified Inflow Angle model to detect hurricane morphology and estimate the wind vector field imaged by cross-polarization SAR. By fitting SHEW to the SAR derived hurricane wind speed, we find the initial closest elliptical-symmetrical wind speed fields, hurricane center location, major and minor axes, the azimuthal (orientation) Angle relative to the reference ellipse, and maximum wind speed. This set of hurricane morphology parameters, along with the speed of hurricane motion, are input to the Inflow Angle model, modified with an ellipse-shaped eye, to derive the hurricane wind direction. A total of 14 RADARSAT-2 ScanSAR images are employed to tune the combined model. Two SAR images acquired over Hurricane Arthur (2014) and Hurricane Earl (2010) are used to validate this model. Comparisons between the modeled surface wind vector and measurements from airborne stepped-frequency microwave radiometer and dropwindsondes show excellent agreement. The proposed method works well in areas with significant radar attenuation by precipitation.
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high resolution hurricane vector winds from c band dual polarization sar observations
Journal of Atmospheric and Oceanic Technology, 2014Co-Authors: Biao Zhang, William Perrie, Jun A Zhang, Eric W UhlhornAbstract:AbstractThis study presents a new approach for retrieving hurricane surface wind vectors utilizing C-band dual-polarization (VV, VH) synthetic aperture radar (SAR) observations. The copolarized geophysical model function [C-band model 5.N (CMOD5.N)] and a new cross-polarized wind speed retrieval model for dual polarization [C-band cross-polarized ocean surface wind retrieval model for dual-polarization SAR (C-2POD)] are employed to construct a cost function. Minimization of the cost function allows optimum estimates for the wind speeds and directions. The wind direction ambiguities are removed using a parametric two-dimensional sea surface Inflow Angle model. To evaluate the accuracy of the proposed method, two RADARSAT-2 SAR images of Hurricanes Bill and Bertha are analyzed. The retrieved wind speeds and directions are compared with collocated Quick Scatterometer (QuikSCAT) winds, showing good consistency. Results suggest that the proposed method has good potential to retrieve hurricane surface wind vect...
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Hurricane Sea Surface Inflow Angle and an Observation-Based Parametric Model
Monthly Weather Review, 2012Co-Authors: Jun A Zhang, Eric W UhlhornAbstract:AbstractThis study presents an analysis of near-surface (10 m) Inflow Angles using wind vector data from over 1600 quality-controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes. The mean Inflow Angle in hurricanes is found to be −22.6° ± 2.2° (95% confidence). Composite analysis results indicate little dependence of storm-relative axisymmetric Inflow Angle on local surface wind speed, and a weak but statistically significant dependence on the radial distance from the storm center. A small, but statistically significant dependence of the axisymmetric Inflow Angle on storm intensity is also found, especially well outside the eyewall. By compositing observations according to radial and azimuthal location relative to storm motion direction, significant Inflow Angle asymmetries are found to depend on storm motion speed, although a large amount of unexplained variability remains. Generally, the largest storm-relative Inflow Angles (
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hurricane sea surface Inflow Angle and an observation based parametric model
Monthly Weather Review, 2012Co-Authors: Jun A Zhang, Eric W UhlhornAbstract:AbstractThis study presents an analysis of near-surface (10 m) Inflow Angles using wind vector data from over 1600 quality-controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes. The mean Inflow Angle in hurricanes is found to be −22.6° ± 2.2° (95% confidence). Composite analysis results indicate little dependence of storm-relative axisymmetric Inflow Angle on local surface wind speed, and a weak but statistically significant dependence on the radial distance from the storm center. A small, but statistically significant dependence of the axisymmetric Inflow Angle on storm intensity is also found, especially well outside the eyewall. By compositing observations according to radial and azimuthal location relative to storm motion direction, significant Inflow Angle asymmetries are found to depend on storm motion speed, although a large amount of unexplained variability remains. Generally, the largest storm-relative Inflow Angles (<−50°) are found in the fas...
Eric W Uhlhorn - One of the best experts on this subject based on the ideXlab platform.
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high resolution hurricane vector winds from c band dual polarization sar observations
Journal of Atmospheric and Oceanic Technology, 2014Co-Authors: Biao Zhang, William Perrie, Jun A Zhang, Eric W UhlhornAbstract:AbstractThis study presents a new approach for retrieving hurricane surface wind vectors utilizing C-band dual-polarization (VV, VH) synthetic aperture radar (SAR) observations. The copolarized geophysical model function [C-band model 5.N (CMOD5.N)] and a new cross-polarized wind speed retrieval model for dual polarization [C-band cross-polarized ocean surface wind retrieval model for dual-polarization SAR (C-2POD)] are employed to construct a cost function. Minimization of the cost function allows optimum estimates for the wind speeds and directions. The wind direction ambiguities are removed using a parametric two-dimensional sea surface Inflow Angle model. To evaluate the accuracy of the proposed method, two RADARSAT-2 SAR images of Hurricanes Bill and Bertha are analyzed. The retrieved wind speeds and directions are compared with collocated Quick Scatterometer (QuikSCAT) winds, showing good consistency. Results suggest that the proposed method has good potential to retrieve hurricane surface wind vect...
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Hurricane Sea Surface Inflow Angle and an Observation-Based Parametric Model
Monthly Weather Review, 2012Co-Authors: Jun A Zhang, Eric W UhlhornAbstract:AbstractThis study presents an analysis of near-surface (10 m) Inflow Angles using wind vector data from over 1600 quality-controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes. The mean Inflow Angle in hurricanes is found to be −22.6° ± 2.2° (95% confidence). Composite analysis results indicate little dependence of storm-relative axisymmetric Inflow Angle on local surface wind speed, and a weak but statistically significant dependence on the radial distance from the storm center. A small, but statistically significant dependence of the axisymmetric Inflow Angle on storm intensity is also found, especially well outside the eyewall. By compositing observations according to radial and azimuthal location relative to storm motion direction, significant Inflow Angle asymmetries are found to depend on storm motion speed, although a large amount of unexplained variability remains. Generally, the largest storm-relative Inflow Angles (
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hurricane sea surface Inflow Angle and an observation based parametric model
Monthly Weather Review, 2012Co-Authors: Jun A Zhang, Eric W UhlhornAbstract:AbstractThis study presents an analysis of near-surface (10 m) Inflow Angles using wind vector data from over 1600 quality-controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes. The mean Inflow Angle in hurricanes is found to be −22.6° ± 2.2° (95% confidence). Composite analysis results indicate little dependence of storm-relative axisymmetric Inflow Angle on local surface wind speed, and a weak but statistically significant dependence on the radial distance from the storm center. A small, but statistically significant dependence of the axisymmetric Inflow Angle on storm intensity is also found, especially well outside the eyewall. By compositing observations according to radial and azimuthal location relative to storm motion direction, significant Inflow Angle asymmetries are found to depend on storm motion speed, although a large amount of unexplained variability remains. Generally, the largest storm-relative Inflow Angles (<−50°) are found in the fas...
Henrique Alves - One of the best experts on this subject based on the ideXlab platform.
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Global scatterometer observations of the structure of tropical cyclone wind fields
Monthly Weather Review, 2020Co-Authors: Ali Tamizi, Ian R. Young, Agustinus Ribal, Henrique AlvesAbstract:AbstractA very large database containing 24 years of scatterometer passes is analysed to investigate the surface wind fields within tropical cyclones. The analysis confirms the left-right asymmetry of the wind field with the strongest winds directly to the right of the tropical cyclone centre (northern hemisphere). At values greater than two times the radius to maximum winds, the asymmetry is approximately equal to the storm velocity of forward movement. Observed wind Inflow Angle (i.e. storm motion not subtracted) is shown to vary both radially and azimuthally within the tropical cyclone. The smallest observed wind Inflow Angles are found in the left-front quadrant with the largest values in the right-rear quadrant. As the velocity of forward movement increases and the central pressure decreases, observed Inflow Angles ahead of the storm decrease and behind the storm increase. In the right-rear quadrant, the observed Inflow Angle increases with radius from the storm centre. In all other quadrants, the observed Inflow Angle is approximately constant as a function of radial distance.
Rob J. Van Der Geest - One of the best experts on this subject based on the ideXlab platform.
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Disturbed diastolic left ventricular Inflow vortex ring formation in patients with corrected atrioventricular septal defect: quantitative three-dimensional vortex core analysis from 4DFlow MRI
Journal of Cardiovascular Magnetic Resonance, 2015Co-Authors: Mohammed S. M. Elbaz, Emmeline E. Calkoen, Arno A.w. Roest, Jos J.m. Westenberg, Rob J. Van Der GeestAbstract:Background Vortex formation in the left ventricle (LV) is suggested to contribute to efficient blood pumping and altered vortex formation is associated with diastolic dysfunction. Patients after atrioventricular septal defect (AVSD) correction present abnormalities in valve morphology and subsequently develop altered Inflow patterns (Calkoen et al. JMRI 2014), which may disturb normal vortex formation. We aimed to analyze vortex ring formation in AVSD-corrected patients compared to healthy controls and to evaluate association with Inflow Angle.
Ali Tamizi - One of the best experts on this subject based on the ideXlab platform.
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Global scatterometer observations of the structure of tropical cyclone wind fields
Monthly Weather Review, 2020Co-Authors: Ali Tamizi, Ian R. Young, Agustinus Ribal, Henrique AlvesAbstract:AbstractA very large database containing 24 years of scatterometer passes is analysed to investigate the surface wind fields within tropical cyclones. The analysis confirms the left-right asymmetry of the wind field with the strongest winds directly to the right of the tropical cyclone centre (northern hemisphere). At values greater than two times the radius to maximum winds, the asymmetry is approximately equal to the storm velocity of forward movement. Observed wind Inflow Angle (i.e. storm motion not subtracted) is shown to vary both radially and azimuthally within the tropical cyclone. The smallest observed wind Inflow Angles are found in the left-front quadrant with the largest values in the right-rear quadrant. As the velocity of forward movement increases and the central pressure decreases, observed Inflow Angles ahead of the storm decrease and behind the storm increase. In the right-rear quadrant, the observed Inflow Angle increases with radius from the storm centre. In all other quadrants, the observed Inflow Angle is approximately constant as a function of radial distance.