Backprojection Autofocus of Large Ships with Arbitrary Motion for Synthetic Aperture Radar

Produktbeschreibung

Radar images of the open sea taken by airborne synthetic aperture radar (SAR) show typically several smeared ships. Due to their non-linear motions on a rough sea, these ships are smeared beyond recognition, such that their images are useless for classification or identification tasks. The ship imaging algorithm presented in this thesis consists of a fast image reconstruction using the fast factorized backprojection algorithm and an extended autofocus algorithm of large moving ships. This thesis analysis the factorization parameters of the fast factorized backprojection algorithm and describes how to choose them nearoptimally in order to reconstruct SAR images with minimal computational costs and without any loss of quality. Furthermore, this thesis shows how to estimate and compensate for the translation, the rotation and the deformation of a large arbitrarily moving ship in order to reconstruct a sharp image of the ship. The proposed autofocus technique generates images in which the ship type can be recognized, which was not possible by state-of-the-art autofocus techniques before.

CONTENTS
1 introduction 1
1.1 Synthetic Aperture Radar . . . . . . . . . . . . . . . . . . . 2
1.2 Fast Factorized Backprojection . . . . . . . . . . . . . . . . 7
1.3 Autofocus of Large Ships . . . . . . . . . . . . . . . . . . . 9
1.4 Structure of the Thesis . . . . . . . . . . . . . . . . . . . . . 12
2 basics of backprojection image reconstruction 13
2.1 Fundamentals of Synthetic Aperture Radar . . . . . . . . . 13
2.2 Signal Model of a Static Scene . . . . . . . . . . . . . . . . 18
2.3 Global Backprojection . . . . . . . . . . . . . . . . . . . . . 24
2.4 Image Quality Metrics . . . . . . . . . . . . . . . . . . . . . 27
2.5 Backprojection Autofocus . . . . . . . . . . . . . . . . . . . 31
2.6 Real Data Example . . . . . . . . . . . . . . . . . . . . . . . 36
3 optimization of fast factorized backprojection 40
3.1 Fast Factorized Backprojection . . . . . . . . . . . . . . . . 41
3.2 Computational Costs . . . . . . . . . . . . . . . . . . . . . . 44
3.3 Exact Range Error Computation . . . . . . . . . . . . . . . 46
3.4 Image Error Estimation . . . . . . . . . . . . . . . . . . . . 51
3.5 Parameter Analysis and Optimization . . . . . . . . . . . . 53
3.6 Optimal Parameter Choice Rule . . . . . . . . . . . . . . . 57
3.7 Experimental Results and Evaluation . . . . . . . . . . . . 59
3.7.1 Narrow Swath SAR using Gotcha data . . . . . . . 60
3.7.2 Squinted SAR using SmartRadar data . . . . . . . 69
4 autofocus of large ships with arbitrary motion 75
4.1 Ship Detection and Location Estimation . . . . . . . . . . . 77
4.2 Signal Model of a Moving Ship . . . . . . . . . . . . . . . . 79
4.3 Effects of Arbitrary Motion on SAR Images . . . . . . . . . 81
4.4 Optimal Focus Using True Motion . . . . . . . . . . . . . . 85
4.5 State-of-the-Art Autofocus of Ships . . . . . . . . . . . . . 87
4.6 Extended Autofocus Algorithm of Large Ships . . . . . . . 90
4.7 Experimental Results and Evaluation . . . . . . . . . . . . 97
4.7.1 Autofocus of a Large Tanker . . . . . . . . . . . . . 98
4.7.2 Autofocus of a Large Bulk Carrier . . . . . . . . . . 101
4.7.3 Autofocus of a Self-Discharging Bulk Carrier . . . 103
4.7.4 Autofocus of a Static Scene with Low-Cost INS . . 107
5 conclusions 112
a appendix 117
bibliography 119

Keywords: Aron Sommer, Synthetic aperture radar (SAR), inverse synthetic aperture radar (ISAR), backprojection, fast factorized backprojection, imaging of moving objects, phase errors, auto-focus, regularization, spotmode, stripmap-mode,