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

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2.5 Radar Imaging Methods Overview 18 30,29,31,131,39,151,44,92]. Most of them present methods for computing dinwall. Even if it looks like a simple task, it is a very complex problem that mostly requires huge computational power. In Section 4.1 we introduce an efficient, precise and fast method how to compute TOA for through the wall scenario. Very simple, fast, but not too precise approximation for compensation of the wall effect is presented in [31]. Here, the time of flight of the wave inside a wall is given by: tinwall = dinwall vw (2.5.3) where vw is the velocity of the signal inside the wall. The approximation of the velocity inside the wall is related to the wall permittivity and permeability given by: vw ≈ 1 √ µwεw = 1 √ µaεaµrwεrw = c √ µrwεrw (2.5.4) where µw and εw are the permeability and permittivity of the wall, µa and εa are the permeability and permittivity of the air, and µrw and εrw are the relative permeability and permittivity of the wall. For non-magnetic materials such as concrete or brick wall, the relative permeability µrw = 1. Hence the velocity in non-magnetic wall is given by: and time in the wall by: vw = c √ εrw √ εrwdinwall (2.5.5) tinwall = . (2.5.6) c With the assumption that the wave mostly penetrates perpendicularly to the wall, the approximation of dinwall can be given by: dinwall ≈ Dw (2.5.7) where Dw is thickness of the wall. Time delay caused by through-wall penetration is then expressed as comparison to through the air propagation: tdelay = Dw vw − Dw c = Dw c (√ εrw − 1) . (2.5.8) All impulse responses BP n should be shifted by tdelay before SAR imaging is applied. Including tdelay into the migration (2.5.2) partly compensates effect of the wall: I(xT , zT ) = 1 N N� BP n (X, k = (T OAn + tdelay)). (2.5.9) n=1 The example of migrated image with and without simple wall compensation is shown in [31]. In general, the targets in compensated image are better focused as well as the positions of objects behind the wall are closer to the real positions.
2.5 Radar Imaging Methods Overview 19 2.5.4 Differential SAR The wall is mostly represented in a long area of the migrated image. Sometimes the objects behind the wall are overlapped by the wall reflection. Differential SAR (DSAR) is a method for elimination of direct reflection from the walls proposed by Mojtaba Dehmollaian et al. [45] in 2009. The idea is similar to applying background subtraction for detection of moving objects behind the wall. Although during SAR scanning all the scanned objects seems to move, the reflection from the first wall is almost the same for two successive antenna positions. However, the reflection from the object behind the wall is not the same, as it can be seen in Fig. 2.5.2. Before the SAR imaging is applied, the matrix of difference signal is Z Antenna at two successive positions Wall reflections TOA W TOA W TOA T Target reflections TOA T+� Target Wall Fig. 2.5.2: Differential SAR model for monostatic approach. obtained by substracting two successive impulse responses: B∆ = VR(n + 1) − VR(n). (2.5.10) Computing the SAR image with B∆ leads to elimination of direct reflection from the first wall. This can increase a signal-to-clutter ratio of small objects behind the wall. The wall has to be homogenous and scan has to be performed in parallel to the wall in order to obtain the same wall reflection in two successive antenna positions. X
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 and 24: 2.3 SAR Scanning 9 and shall remain
Page 25 and 26: 2.4 Calibration and Preprocessing 1
Page 27 and 28: 2.4 Calibration and Preprocessing 1
Page 29 and 30: 2.5 Radar Imaging Methods Overview
Page 31: 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
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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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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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