 | Madrigal O.P. Multicircular holographic SAR tomography over forested: Diss. zur … Dr.-Ing. / Deutsches Zentrum für Luft- und Raumfahrt, Institut für Flugfuhrung, Braunschweig. - Köln: DLR, 2017. - XXXI,162 p. : ill. - (Forschungsbericht; 2016-59). - Res. also Germ. - Bibliogr.: p. 147-160. - ISSN 1434-8454
Шифр: (Pr 1120/2016-59) 02
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Abstract ....................................................... ix
Kurzfassung .................................................... xi
List of figures ............................................. xxiii
List of tables ................................................ xxv
1 Introduction ............................................... 1
1.1 Radar remote sensing ....................................... 1
1.2 Circular and multicircular SAR acquisitions ................ 3
1.3 Thesis contribution ........................................ 7
1.3.1 Objectives, scope and justification ................. 7
1.3.2 Outline ............................................. 9
2 Synthetic Aperture Radar .................................. 11
2.1 SAR resolution ............................................ 11
2.1.1 Range resolution ................................... 11
2.1.2 Azimuth resolution for Stripmap and Spotlight SAR .. 13
2.2 SAR processing ............................................ 15
2.2.1 Nominal range imaging .............................. 16
2.2.2 Nominal azimuth imaging ............................ 16
2.3 SAR interferometry ........................................ 19
2.3.1 Across-track interferometry (XTI) ................. 19
2.4 SAR polarimetry ........................................... 24
2.5 Tomography ................................................ 27
2.5.1 Analogy with spotlight SAR ......................... 27
2.5.2 SAR tomography ..................................... 28
3 Circular Synthetic Aperture Radar ......................... 35
3.1 Impulse response function (IRF) ........................... 35
3.1.1 Target in the center ............................... 37
3.1.2 Target off the center .............................. 40
3.1.3 Pulse repetition frequency ......................... 42
3.2 Geometric resolutions ..................................... 43
3.3 Topography dependency ..................................... 45
3.4 Multicircular acquisitions ................................ 46
3.5 Focusing algorithms ....................................... 46
3.5.1 Wavefront reconstruction ........................... 47
3.5.2 Time-domain direct back-projection (DBP) ........... 49
3.5.3 Generalised likelihood ratio test (GLRT) ........... 51
3.5.4 Compressive sensing (CS) reconstruction ............ 52
3.6 Autofocus algorithms ...................................... 56
3.6.1 Phase gradient autofocusing (PGA) .................. 56
3.6.2 Maximum-likelihood estimation for PGA .............. 58
3.6.3 Frequency-domain autofocus ......................... 60
4 Fast Factorised Back-Projection for CSAR .................. 63
4.1 FFBP for linear SAR imaging modes ......................... 63
4.1.1 Fast back-projection ............................... 63
4.1.2 Fast factorised back-projection .................... 65
4.2 FFBP for circular trajectories ............................ 68
4.2.1 Geometry ........................................... 69
4.2.2 Methodology ........................................ 69
4.2.3 Sampling requirements .............................. 71
4.2.4 Computational burden ............................... 73
4.2.5 Assessment with simulated data ..................... 74
4.2.6 Practical implementation ........................... 74
5 Fully Polarimetrie High-Resolution 3-D Imaging with
Circular SAR .............................................. 77
5.1 Circular L-band campaign .................................. 77
5.2 FFBP assessment with real data ............................ 78
5.3 Incoherent versus coherent imaging ........................ 80
5.4 Stripmap versus CSAR ...................................... 83
5.5 3-D CSAR reconstruction ................................... 84
6 Fully Polarimetrie Holographic SAR Tomography with
Multicircular Acquisitions ................................ 93
6.1 Holographic SAR tomography (HoloSAR) ...................... 93
6.1.1 HoloSAR with mutlicircular acquisitions ............ 93
6.1.2 The 3-D projection-slice theorem ................... 96
6.1.3 Impulse response function (IRF) .................... 97
6.1.4 Sidelobe analysis and geometric resolutions ........ 99
6.1.5 Frequency domain analysis of the IRF .............. 101
6.2 Focusing approaches of HoloSAR ........................... 103
6.2.1 Coherent imaging .................................. 105
6.2.2 Subaperture-based processing ...................... 106
6.3 SVD-based phase calibration .............................. 110
6.4 Holographic SAR tomography at P-band ..................... 111
6.4.1 Multicircular P-band campaign ..................... 111
6.4.2 Experimental results .............................. 113
6.5 Holographic SAR tomography at L-band ..................... 117
6.5.1 Multicircular L-band campaign ..................... 118
6.5.2 PGA-based autofocusing ............................ 120
6.5.3 Impulse response function: Lьneburg lens .......... 125
6.5.4 Single tree at 3-D high resolution ................ 127
6.5.5 Study of processing strategies .................... 128
7 Conclusions and Outlook .................................. 133
7.1 Future work .............................................. 135
A Appendix ................................................. 141
A.l DLR's SAR systems: E-SAR and F-SAR ....................... 141
A.2 Experimental realisation with E-SAR and F-SAR ............ 142
A.3 Special functions ........................................ 142
A.3.1 Gamma function .................................... 143
A.3.2 Bessel function ................................... 143
A.3.3 Hankel function ................................... 144
A.3.4 Analysis of the 3-D back-projection equation ...... 144
Bibliography .................................................. 147
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