Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE

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2.4 Calibration and Preprocessing 10 Z SXZ ( , ) Motion X TX RX TX RX tr tr [ x,z re re] [ x,z] E 1 T= [ x T,zT] E 2 n BXn ( , ) Hyperbola a) b) Fig. 2.3.1: a) 2D SAR spatial model. b) B-scan of one point. The basic 2D SAR spatial model is shown in Fig. 2.3.1 a). A transmitted wave is reflected from the target to all directions uniformly. Because the antenna beam is wide, the signal reflected from the target is received not only when the antenna system is exactly over the target, but in a lot of positions that allow to ”see” the target. This will cause that one point in S(X, Z) space will be represented in an acquired B-scan B(X, n) (set of A-scans assembled together in a 2D structure) as a hyperbola, as it is show in Fig. 2.3.1 b). The X is scanning direction and Z is looking direction. 2.4 Calibration and Preprocessing There are several types of calibrations and preprocessing methods that help us to remove some unwanted artifacts from measured data. The most important are: oversampling in time domain, time zero estimation, crosstalk removing and deconvolution. Such signal processing methods affect the imaging results on a large scale. For example crosstalk does not contain any information about the scanned object and should be removed. Time zero estimation is very important for correct focusing measured hyperbolas back to the one point, which will be described in Section 2.5. An image of the investigated object would be blurred, if time zero estimation is incorrect even in a few chips. All of these calibration and preprocessing methods are applied individually to the A-scans. 2.4.1 Time Domain Interpolation The measured B-scan B(X, n) (Fig. 2.4.1 a)) is oversampled by the cubic spline interpolation [83] with an oversampling factor KO in the discrete time domain, so X
2.4 Calibration and Preprocessing 11 Amplitude Amplitude Amplitude Amplitude Amplitude 0.5 0 -1 0.5 0 -1 0.5 0 -1 �[ k] 0.5 0 -1 0.5 0 Crosstalk a) Measured A-scan 5 10 15 20 25 30 35 tns [ ] b) Interpolated A-scan �[ k] Crosstalk Crosstalk Wall Wall 5 10 15 20 25 30 35 tns [ ] c) Shifted to the time zero Wall 5 10 15 20 25 30 35 tns [ ] d) Crosstalk removed Wall 5 10 15 20 25 30 35 tns [ ] e) After deconvolution Wall Object behind the wall Object behind the wall Object behind the wall Object behind the wall Object behind the wall 5 10 15 20 25 30 35 tns [ ] INTERPOLATION SHIFT TO TIME ZERO REMOVE CROSSTALK DECONVOLUTION Fig. 2.4.1: Preprocessing and calibration steps: a) Measured A-scan. b) Interpolated A-scan. c) Shift to time zero. d) Crosstalk removed. e) After deconvolution. the interpolated B-scan Bs(X, k) is obtained (Fig. 2.4.1 b)): Bs(X, k) = Spline(B(X, n), KO), k = nKO − KO + 1 (2.4.1)
Page 1 and 2: TECHNICAL UNIVERSITY OF KOˇSICE Fa
Page 3 and 4: Acknowledgement I give a sincere gr
Page 5 and 6: CONTENTS v 3 Goals of Dissertation
Page 7 and 8: LIST OF FIGURES vii List of Figures
Page 9 and 10: LIST OF FIGURES ix 4.4.3 Aquarium f
Page 11 and 12: LIST OF FIGURES xi List of Symbols
Page 13 and 14: LIST OF FIGURES xiii kx - Horizonta
Page 15 and 16: Chapter 1 Introduction 1.1 Motivati
Page 17 and 18: 1.3 Thesis Organization 3 In additi
Page 19 and 20: Chapter 2 State Of The Art 2.1 UWB
Page 21 and 22: 2.2 Through-Wall Radar Basic Model
Page 23: 2.3 SAR Scanning 9 and shall remain
Page 27 and 28: 2.4 Calibration and Preprocessing 1
Page 29 and 30: 2.5 Radar Imaging Methods Overview
Page 55 and 56: Chapter 4 Selected Research Methods
Page 57 and 58: 4.1 Through-Wall TOA Estimation 43
Page 71 and 72: 4.2 Measurements of the Wall Parame
Page 73 and 74: 4.2 Measurements of the Wall Parame
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4.2 Measurements of the Wall Parame
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4.3 Highlighting of a Building Cont
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4.4 Measurements of the Practical S
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5.1 Conclusion and Future Work 85 5
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50 100 150 200 250 300 350 400 Z 45
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50 100 150 200 250 300 350 400 Z 45
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50 100 150 200 250 300 350 400 Z 45
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50 100 150 200 250 300 350 400 Z 45
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Z [cm] Z [cm] 50 100 150 200 250 30
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Z [cm] 50 100 150 200 250 300 b) Em
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BIBLIOGRAPHY 99 [13] T. W. Barrett,
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BIBLIOGRAPHY 101 [46] G. Derveaux,
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BIBLIOGRAPHY 103 [81] S. Kidera, T.
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BIBLIOGRAPHY 105 [115] J. Sachs, M.
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BIBLIOGRAPHY 107 [150] O. Yilmaz, S
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Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE

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