Inverse Synthetic Aperture Radar Imaging: Principles, Algorithms, and Applications

304 Pages·2014·4.75 MB·English

by  Victor C. Chen

Inverse Synthetic Aperture
Radar Imaging

Inverse Synthetic Aperture
Radar Imaging
Principles, Algorithms and Applications
Victor C. Chen
Ancortek Inc. USA
US Naval Research Laboratory, retired
Marco Martorella
Department of Information Engineering
University of Pisa
Edison, NJ
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Contents
Preface ix
List of Abbreviations and Symbols xi
1 Introduction to ISAR Imaging 1
1.1 SAR and ISAR Concepts at a Glance 2
1.2 Brief Historical Overview of SAR and ISAR 5
1.3 Fundamentals of ISAR Imaging 6
1.4 ISAR Image Resolution 15
1.5 Main Differences between ISAR and Optical Images 16
1.6 Conclusions 18
References 19
2 Basic Principles of ISAR Imaging 21
2.1 ISAR Scattering Model 21
2.2 ISAR Signal Waveforms 25
2.3 Radar Ambiguity Function 37
2.4 Matched Filter 39
2.5 Point Spread Function in ISAR Imaging 41
2.6 ISAR Image Projection Plane 43
2.7 ISAR Image Processing 47
2.8 Bistatic ISAR 51
References 55
v
vi Contents
3 ISAR Image Formation 57
3.1 ISAR Range-Doppler Image Formation 57
3.2 Time-Frequency–Based Image Formation 67
3.3 Display 2-D ISAR Imagery—Windowing and
Zero Padding for Sidelobe Suppression 74
References 75
4 ISAR Motion Compensation 77
4.1 Translational Motion Compensation 77
4.2 Rotational Motion Compensation 94
References 102
5 ISAR Autofocus Algorithms 105
5.1 Prominent Point Processing Autofocus 105
5.2 Phase Gradient Autofocus Algorithm 114
5.3 Image Contrast-Based Autofocus 116
5.4 Entropy Minimization–Based Autofocus 124
5.5 Keystone Transform in ISAR 126
References 131
6 Signal Processing Issues in ISAR Imaging 133
6.1 ISAR Imaging in the Presence of Target’s Complex Motion 133
6.2 ISAR Imaging in the Presence of Strong Noise and Clutter 138
6.3 Sidelobes and Their Reduction and Cancellation in ISAR
Imaging 150
References 159
7 ISAR Target Feature Extraction 161
7.1 Feature Extraction from 2-D ISAR Imagery 163
7.2 Extraction of Micro-Doppler Features from ISAR Data 166
7.3 Summary 174
References 175
8 ISAR Imaging for Refocusing Moving Targets
in SAR Images 177
8.1 Review of Spotlight SAR Algorithms 179
8.2 Projection of SAR Image onto Wavenumber
Domain—Inversion Mapping 185
Contents vii
8.3 Examples 188
References 196
9 FMCW ISAR 199
9.1 FMCW Radar for SAR and ISAR Imaging 199
9.2 FMCW ISAR Received Signal Model 201
9.3 FMCW ISAR Processing 203
9.4 Example of FMCW ISAR Autofocusing 210
References 213
10 Bistatic ISAR 215
10.1 Basics of ISAR Imaging 215
10.2 Geometry and Modeling 217
10.3 Bistatically Equivalent Monostatic ISAR Geometry 218
10.4 Bistatic ISAR Image Formation 219
10.5 Bistatic ISAR Image Interpretation 222
10.6 The Effect of Synchronization Errors on B-ISAR Imaging 224
10.7 Examples 232
10.8 Multistatic ISAR 241
References 245
11 Polarimetric ISAR 247
11.1 Signal Model 248
11.2 Image Formation and Point Spread Function 250
11.3 Polarimetric ISAR Image Autofocus 251
11.4 Polarimetric ISAR Image Interpretation 255
References 258
12 Applications of ISAR Imaging 261
12.1 Case Study 1: Ground-Based ISAR Images of a
Noncooperative Sailing Ship 262
12.2 Case Study 2: Airborne ISAR Imaging of a
Noncooperative Cargo Ship 267
12.3 Case Study 3: Dual Ground-Based/Satellite ISAR Imaging
of a Noncooperative Sailing Ship 270
viii Contents
12.4 Case Study 4: Ground-Based ISAR Imaging of Airplanes 271
12.5 Case Study 5: Extraction of Doppler Features from ISAR
Data of Small Vessels in Sea Clutter 274
References 281
Index 283
Preface
Inversesyntheticapertureradar(ISAR)imaginghasbeenthefocusofmanyresearchersand
operational users in the last few decades. Starting from the 1970s, researchers began to
investigate radar imaging of a target on a rotating turntable, and then a concept of inverse
SAR(ISAR)imaging wasproposed.Shortlyafter that, ISARsystemswerebuilt, andISAR
imaging of ships and aircraft was successfully demonstrated. The main idea behind the
concept of ISAR imaging is to exploit Doppler information induced by the rotation of tar-
gets, which allows for echoes returned from different parts of the target to be distinguished
fromeachother.ThismakesISARsystemsdifferentfromotherimagingsystems,including
direct synthetic aperture radar (SAR) systems. Although SAR and ISAR share the same
underlying concept of forming a synthetic aperture, they are substantially different in the
way they process the radar received signal and generate a focused image of a target. The
importance of ISAR is its potential to form radar images of targets without knowing their
motion parameters. Such targets are generally referred to as noncooperative targets. Thus,
ISARisable to handle a class of scenarios that conventional SARcannot.
Because of the nature of ISAR, most early works were of military interests and classi-
fied. Since late 1980s,somebooksthatinclude ISARtopics have been published[1,2],and
more and more publications on ISAR topics have begun to appear in conferences and
journals.
Thisbookisbasedonour20years’research workonISARimaging ofmovingtargets
and noncooperative target recognition. The goal of this book is to provide readers with a
basic concept of the principles of ISAR imaging of noncooperative targets and a working
knowledge of various algorithms of ISAR imaging formation and autofocus. Therefore, a
large part of this book is devoted to the basic concepts and mathematical models of ISAR
imaging, basic algorithms for motion compensation, ISAR image formation, and image
autofocusing. Chapter 1 is an introduction to the concept of ISAR imaging. Chapter 2 dis-
cusses the basic principles of ISAR imaging, including ISAR scattering model, signal
waveforms,pointspreadfunction,imageprojectionplane,cross-rangefocusprocessing,and
bistatic ISAR. Chapters 3 through 5 are dedicated to detailed algorithms of ISAR image
formation, motion compensation,and autofocus.
The second part of the book discusses more recent research work on ISAR imaging.
Details about ISAR signal processing issues are included in Chapter 6, whereas Chapter 7
deals with feature extraction. Chapter 8 describes a new technique of refocusing moving
ix