scholarly journals A novel reconstruction technique for two-dimensional Bragg scatter imaging

2021 ◽  
Author(s):  
James Webber ◽  
Eric L. Miller
Keyword(s):  
Reconstruction Technique ◽  
Two Dimensional

scholarly journals Inverse reconstruction technique based on time-dependent Petschek-type reconnection model: first application to THEMIS magnetotail observations

2009 ◽  
Vol 27 (12) ◽  
pp. 4369-4377
Author(s):  
V. Ivanova ◽  
J. Liu ◽  
S. Kiehas ◽  
V. Semenov ◽  
H. Biernat
Keyword(s):  
Electric Field ◽  
Total Duration ◽  
Time Dependent ◽  
Reconstruction Technique ◽  
Field Variation ◽  
Magnetic Field Variation ◽  
Two Dimensional ◽  
Line Position ◽  
Inverse Reconstruction ◽  
Reconnection Model

Abstract. We apply the inverse reconstruction technique based on the two-dimensional time-dependent Petschek-type reconnection model to a dual bipolar magnetic structure observed by THEMIS B probe in the Earth's magnetotail during a substorm on 22 February 2008 around 04:35 UT. The technique exploits the recorded bipolar magnetic field variation as an input and provides the reconnection electric field and the location of the X-line as an output. As a result of the technique application, we get (1) the electric field, reaching ~1.1 mV/m at the maximum and consisting of two successive pulses with total duration of ~6 min, and (2) the approximate X-line position located in the magnetotail between 18 and 20 RE.

scholarly journals Reconstruction of two-dimensional magnetopause structures from Cluster observations: verification of method

2004 ◽  
Vol 22 (4) ◽  
pp. 1251-1266 ◽  
Author(s):  
H. Hasegawa ◽  
B. U. Ö. Sonnerup ◽  
M. W. Dunlop ◽  
A. Balogh ◽  
S. E. Haaland ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Minimum Variance ◽  
Reconstruction Technique ◽  
Current Layer ◽  
Two Dimensional ◽  
Magnetic Islands ◽  
Maximum Variance ◽  
Spacecraft Trajectory ◽  
Shafranov Equation ◽  
Mathematical Techniques

Abstract. A recently developed technique for reconstructing approximately two-dimensional (∂/∂z≈0), time-stationary magnetic field structures in space is applied to two magnetopause traversals on the dawnside flank by the four Cluster spacecraft, when the spacecraft separation was about 2000km. The method consists of solving the Grad-Shafranov equation for magnetohydrostatic structures, using plasma and magnetic field data measured along a single spacecraft trajectory as spatial initial values. We assess the usefulness of this single-spacecraft-based technique by comparing the magnetic field maps produced from one spacecraft with the field vectors that other spacecraft actually observed. For an optimally selected invariant (z)-axis, the correlation between the field components predicted from the reconstructed map and the corresponding measured components reaches more than 0.97. This result indicates that the reconstruction technique predicts conditions at the other spacecraft locations quite well. The optimal invariant axis is relatively close to the intermediate variance direction, computed from minimum variance analysis of the measured magnetic field, and is generally well determined with respect to rotations about the maximum variance direction but less well with respect to rotations about the minimum variance direction. In one of the events, field maps recovered individually for two of the spacecraft, which crossed the magnetopause with an interval of a few tens of seconds, show substantial differences in configuration. By comparing these field maps, time evolution of the magnetopause structures, such as the formation of magnetic islands, motion of the structures, and thickening of the magnetopause current layer, is discussed. Key words. Magnetospheric physics (Magnetopause, cusp, and boundary layers) – Space plasma physics (Experimental and mathematical techniques, Magnetic reconnection)

scholarly journals Resistive MHD reconstruction of two-dimensional coherent structures in space

2010 ◽  
Vol 28 (11) ◽  
pp. 2113-2125 ◽  
Author(s):  
W.-L. Teh ◽  
B. U. Ö. Sonnerup ◽  
J. Birn ◽  
R. E. Denton
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Synthetic Data ◽  
Two Dimensions ◽  
Mhd Equations ◽  
Numerical Code ◽  
Reconstruction Technique ◽  
Two Dimensional ◽  
Geomagnetic Tail ◽  
Spacecraft Spin

Abstract. We present a reconstruction technique to solve the steady resistive MHD equations in two dimensions with initial inputs of field and plasma data from a single spacecraft as it passes through a coherent structure in space. At least two components of directly measured electric fields (the spacecraft spin-plane components) are required for the reconstruction, to produce two-dimensional (2-D) field and plasma maps of the cross section of the structure. For convenience, the resistivity tensor η is assumed diagonal in the reconstruction coordinates, which allows its values to be estimated from Ohm's law, E+v×B=η·j. In the present paper, all three components of the electric field are used. We benchmark our numerical code by use of an exact, axi-symmetric solution of the resistive MHD equations and then apply it to synthetic data from a 3-D, resistive, MHD numerical simulation of reconnection in the geomagnetic tail, in a phase of the event where time dependence and deviations from 2-D are both weak. The resistivity used in the simulation is time-independent and localized around the reconnection site in an ellipsoidal region. For the magnetic field, plasma density, and pressure, we find very good agreement between the reconstruction results and the simulation, but the electric field and plasma velocity are not predicted with the same high accuracy.

scholarly journals A relation between algebraic and transform-based reconstruction technique in computed tomography

2013 ◽  
Vol 11 ◽  
pp. 95-100
Author(s):  
S. Kiefhaber ◽  
M. Rosenbaum ◽  
W. Sauer-Greff ◽  
R. Urbansky
Keyword(s):  
Computed Tomography ◽  
Signal Processing ◽  
Sparse Matrices ◽  
Fine Tuning ◽  
Reconstruction Technique ◽  
Algebraic Reconstruction Technique ◽  
Two Dimensional ◽  
Memory Usage ◽  
Application Specific ◽  
Theoretical Insight

Abstract. In this contribution a coherent relation between the algebraic and the transform-based reconstruction technique for computed tomography is introduced using the mathematical means of two-dimensional signal processing. There are two advantages arising from that approach. First, the algebraic reconstruction technique can now be used efficiently regarding memory usage without considerations concerning the handling of large sparse matrices. Second, the relation grants a more intuitive understanding as to the convergence characteristics of the iterative method. Besides the gain in theoretical insight these advantages offer new possibilities for application-specific fine tuning of reconstruction techniques.

scholarly journals Acoustic tomography in the atmospheric surface layer

1999 ◽  
Vol 17 (1) ◽  
pp. 139-148 ◽  
Author(s):  
A. Ziemann ◽  
K. Arnold ◽  
A. Raabe
Keyword(s):  
Surface Layer ◽  
Travel Time ◽  
Atmospheric Surface Layer ◽  
Sound Propagation ◽  
Measuring System ◽  
Acoustic Tomography ◽  
Reconstruction Technique ◽  
Two Dimensional ◽  
Sound Waves ◽  
Atmospheric Conditions

Abstract. Acoustic tomography is presented as a technique for remote monitoring of meteorological quantities. This method and a special algorithm of analysis can directly produce area-averaged values of meteorological parameters. As a result consistent data will be obtained for validation of numerical atmospheric micro-scale models. Such a measuring system can complement conventional point measurements over different surfaces. The procedure of acoustic tomography uses the horizontal propagation of sound waves in the atmospheric surface layer. Therefore, to provide a general overview of sound propagation under various atmospheric conditions a two-dimensional ray-tracing model according to a modified version of Snell's law is used. The state of the crossed atmosphere can be estimated from measurements of acoustic travel time between sources and receivers at different points. Derivation of area-averaged values of the sound speed and furthermore of air temperature results from the inversion of travel time values for all acoustic paths. Thereby, the applied straight ray two-dimensional tomographic model using SIRT (simultaneous iterative reconstruction technique) is characterised as a method with small computational requirements, satisfactory convergence and stability properties as well as simple handling, especially, during online evaluation.Key words. Meteorology and atmospheric dynamics (turbulence; instruments and techniques).

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