Introduction to Sensors for Ranging and Imaging

Dr. Graham Brooker

S SCITEOT puBLisHmefiNC.

SciTech Publishing, Inc Raleigh, NC

www.scitechpub.com

Table of Contents

Introduction to Sensors for Ranging and Imaging

Chapter 1 Introduction to Sensing

1.1 Introduction 1

1.1.1 Active Sensors 1

1.1.2 Passive Sensors 1

1.2 A Brief History of Sensing 2

1.2.1 Sonar 2 1.2.2 Radar 4 1.2.3 Lidar 10

1.3 Passive Infrared Sensing 12 1.4 Sensor Systems 14 1.5 Frequency Band Allocations for the Electromagnetic Spectrum 1.6 Frequency Band Allocations for the Acoustic Spectrum 19 1.7 References 21

Chapter 2 Signal Processing and Modulation

2.1 The Nature of Electronic Signals 2 3

2.1.1 Static and Quasi-Static Signals 23 2.1.2 Periodic and Repetitive Signals 23

2.1.3 Transient and Quasi Transient Signals 23

2.2 Noise 24

2.2.1 Thermal Noise 24

2.2.1.1 Noise Power Spectrum for Thermal Noise 25

2.2.2 Shot Noise 26

2.2.2.1 Noise Power Spectrum for Shot Noise 27

2.2.3 1/f Noise 27 2.2.4 Avalanche Noise 28

2.3 Signals 28

2.4 Signals and Noise in the Frequency Domain 28

2.4.1 The Fourier Series 30

2.5 Sampled Signals 33

2.5.1 Generating Signals in MATLAB 35 2.5.2 Aliasing 37

VI Table of Contents

2.6 Filtering 38

2.6.1 Filter Categories 39

2.6.1.1 Butterworth 40 2.6.1.2 Chebyshev 40 2.6.1.3 Bessel 40 2.6.1.4 Elliptic 40

2.6.2 Filter Roll-off 40

2.6.3 The Ear as a Filter Bank 41

2.7 Analog Modulation and Demodulation 41

2.7.1 Amplitude Modulation 42

2.8 Frequency Modulation (FM) 45 2.9 Linear Frequency Modulation 50 2.10 Pulse Coded Modulation Techniques 52

2.10.1 Pulse Amplitude Modulation 52 2.10.2 Frequency Shift Keying 55 2.10.3 Phase Shift Keying 57 2.10.4 Stepped Frequency Modulation 60

2.11 Convolution 61

2.11.1 Linear Time Invariant Systems 61 2.11.2 The Convolution Sum 63 2.11.3 Worked Example: Pulsed Radar Echo Amplitude 65

2.12 References 67

Chapter 3 IR Radiometers & Image Intensifies ' 69

3.1 Introduction 69 3.2 Thermal Emission 70

3.2.1 Blackbody Radiation 70 3.2.2 The Planck Function 70 3.2.3 Properties of the Planck Function 71 3.2.4 Confirmation of Stefan-Boltzmann and Rayleigh-Jean Laws 74

3.3 Emissivity and Reflectivity 76

3.3.1 Worked Example: Black Body Radiation from Human Body 78

3.4 Detecting Thermal Radiation 79

3.4.1 External Photoeffect 80 3.4.2 Internal Photoeffect 80

3.4.2.1 Photoconductive Detectors 80 3.4.2.2 Photovoltaic Detectors 81

3.5 Heating 82

3.5.1 Bolometers 82 3.5.2 Pyroelectric Sensors 83 3.5.3 Thermopiles 84

Table of Contents VII

3.6 Performance Criteria for Detectors 85

3.6.1 Responsivity 85 3.6.2 Noise Equivalent Power (NEP) 87 3.6.3 Detectivity and Specific Detectivity 87

3.7 Noise Processes and Effects 88 3.8 Applications 89

3.8.1 Passive Ultraviolet Sensor (External Photoeffect) 89 3.8.2 Radiation Thermometer (Internal Photoeffect:

Thermopile) 90 3.8.3 Passive Infrared Sensor (Internal Photoeffect: Pyroelectric) 91 3.8.4 Crookes' Radiometer 92

3.9 Introduction to Thermal Imaging Systems 93

3.9.1 Scattering and Absorption 93 3.9.2 Scanning Mechanisms and Arrays 95 3.9.3 Micro-bolometer Arrays 96 3.9.4 Key Optical Parameters 97

3.10 Performance Measures for Infrared Imagers 98

3.10.1 Detector Field of View 98 3.10.2 Spatial Frequency 100 3.10.3 Signal to Noise Ratio for a Point Target 102 3.10.4 Worked Example: IRST System SNR 103 3.10.5 Signal to Noise Ratio for a Target in Ground Clutter 104 3.10.6 Noise Equivalent Temperature Difference (NETD) 105 3.10.7 Example 105 3.10.8 The Minimum Resolvable Temperature Difference

(MRTD) 107

3.11 Target Detection and Recognition 107

3.11.1 Example of FLIR Detection 109

3.12 Thermal Imaging Applications 112 3.13 Image Intensifiers 114

3.13.1 First Generation Tubes 114 3.13.2 Second Generation Tubes 115 3.13.3 Limitations of MicroChannel Plates 116 3.13.4 Third Generation Tubes 117 3.13.5 Spectral Characteristics of die Scene 117 3.13.6 Time Gating MicroChannel Plates 117

3.14 References 119

Chapter 4 Millimeter Wave Radiometers

4.1 Antenna Power Temperature Correspondence 121

4.1.1 Example of Power Received from a Blackbody 123

121

Table of Contents

4.2 Brightness Temperature 123 4.3 Apparent Temperature 123 4.4 Atmospheric Effects 125

4.4.1 Attenuation 125 4.4.2 Downwelling Radiation 125 4.4.3 Upwelling Radiation 125

4.5 Terrain Brightness 127

4.6 Worked Example: Space-based Radiometer 127

4.6.1 Temperature Contrast 128

4.7 Antenna Considerations 128

4.7.1 Beamwidth 128 4.7.2 Efficiency 128

4.7.3 Fill Ratio 129

4.8 Receiver Considerations 129

4.8.1 Mixer Implementations for Microwave Receivers 129

4.8.1.1 Mixer Specifications 130

4.8.2 Noise Figure 130

4.9 The System Noise Temperature 131 4.10 Radiometer Temperature Sensitivity 131 4.11 Radiometer Implementation 133

4.11.1 Total Power Radiometer 134 4.11.2 Dicke Radiometer 135 4.11.3 Performance Comparison between Radiometer Types 135

4.12 Intermediate Frequency and Video Gain Requirements 135 4.13 Worked Example: Anti Tank Submunition Sensor Design 135

4.13.1 Radiometer Implementation 142 4.13.2 Receiver Noise Temperature 142

4.13.3 Minimum Detectable Temperature Difference 143

4.14 Radiometric Imaging 144

4.14.1 Image Processing 144

4.15 Applications 147

4.15.1 Airborne Scanned Millimeter Wave Radiometer 148 4.15.2 Scanning Multi-channel Microwave Radiometer

(SMMR) 149 4.15.3 Ground Based Millimeter Wave Radiometers 150

4.15.3.1 Low Visibility Imaging 150 4.15.3.2 Concealed Weapon Detection 152 4.15.3.3 Surveillance and Law Enforcement 154 4.15.3.4 Medical Imaging 154

4.15.4 Radio Astronomy 155

4.15.4.1 Single Dish Telescopes 156

Table of Contents IX

4.15.4.2 Telescope Arrays 156

4.15.4.3 Applications 157

4.16 References 158

Chapter 5 Active Ranging Sensors 161

5.1 Overview 161 5.2 Triangulation 161 5.3 Pulsed Time-of-Flight Operation 164

5.3.1 Sensor Requirements 165 5.3.2 Speed of Propagation 166 5.3.3 The Antenna 167 5.3.4 The Transmitter 170

5.3.4.1 Radar Transmitters 172 5.3.4.2 Underwater Sonar Transmitters 175 5.3.4.3 Ultrasonic Transmitters 176 5.3.4.4 Laser Transmitters 179

5.3.5 The Receiver 182

5.4 Pulsed Range Measurement 187

5.4.1 Timing Discriminators 188 5.4.2 Pulse Integration 191

5.4.3 Time Transformation 194

5.5 Other Methods to Measure Range 194

5.5.1 Ranging using an Unmodulated Carrier 195 5.5.2 Ranging using a Modulated Carrier 195

5.5.3 Tellurometer Example 197

5.6 The Radar Range Equation 199

5.6.1 Derivation 199 5.6.2 The dB Form 201 5.6.3 Worked Example: Radar Detection Calculation 202 5.6.4 Receiver Noise 204 5.6.5 Determining the Required Signal Level 204 5.6.6 Pulse integration and the probability of detection 206

5.7 The Acoustic Range Equation 207

5.7.1 Example of Using the Acoustic Range Equation 209

5.8 TOF Measurement Considerations 210 5.9 Range Measurement Radar for a Cruise 210 5.10 References 212

Chapter 6 Active Imaging Sensors 215

6.1 Imaging Techniques 215 6.2 Range-Gate limited 2D Image Construction 216

X Table of Contents

6.3 Beamwidth Limited 3D Image Construction 219

6.3.1 Push-Broom Scanning 219 6.3.2 Mechanical Scanning 219

6.4 The Lidar Range Equation 222

6.5 Lidar System Performance 223

6.5.1 Direct Detection 224

6.5.1.1 Direct Detection Photodiodes 225 6.5.2 Heterodyne Detection 226 6.5.3 Signal to Noise Ratio and Detection Probability 227 6.5.4 Worked Example: Laser Radar Reflection from the

Moon 228

6.6 Digital Terrain Models 230

6.6.1 Surface Models 231 6.6.2 Digital Landscapes 231 6.6.3 Thematic Visualization 232

6.6.3.1 Geographic Information Systems 233 6.6.3.2 3D City Models 233

6.7 Airborne Lidar Hydrography 234 6.8 3D Imaging 235

6.8.1 Radar Systems 236 6.8.2 Focused Beam Radar Imaging 237 6.8.3 Lidar Imaging 240 6.8.4 Jigsaw—Foliage Penetrating Lidar 243

6.9 Acoustic Imaging 244 '

6.9.1 Scanning Acoustic Microscopes 244

6.10 Worked Example: Lidar Locust Tracker 245

6.10.1 Requirement 245 6.10.2 Specifications 247 6.10.3 System Hardware 247 6.10.4 Determining the Required Aircraft Speed 247 6.10.5 Laser Power Density on the Ground 248 6.10.6 The power density of the reflected signals back at the

laser 249 6.10.7 The Effect of the Sun 250 6.10.8 The Receiver 252 6.10.9 Conclusions 254

6.11 References 254

Chapter 7 Signal Propagation 257

7.1 The Sensing Environment 257

7.2 Attenuation of Electromagnetic Waves 257

7.2.1 Clear Weather Attenuation 259

Table of Contents XI

7.2.2 Effect of Atmospheric Pressure (air density) 260 7.2.3 Effect of Rain 260 7.2.4 Effect of Fog and Clouds 262 7.2.5 Overall Attenuation 265 7.2.6 Attenuation through Dust and Smoke 266

7.2.6.1 Attenuation of Radar Signals 267 7.2.6.2 Attenuation of Laser Signals 268

7.2.7 Effect of atmosphere composition 271 7.2.8 Electromagnetic propagation through solid 272

7.3 Refraction of Electromagnetic Waves 273 7.4 Acoustics and Vibration 274

7.4.1 Characteristic Impedance (Z) and Sound Pressure 275 7.4.2 Sound Intensity (I) 275 7.4.3 Sound Propagation in Gases 276

7.4.3.1 Worked Example: Effect of Molecular Weight on Speed of Sound 277

7.4.3.2 Effect of Temperature and Pressure 277

7.4.4 Sound Propagation in Water 278 7.4.5 Sound Propagation in Solids 280 7.4.6 Attenuation of Sound in Air 282

7.5 Attenuation of Sound in Water 284 7.6 Reflection and Refraction of Sound 287

7.6.1 Waves normal to the Interface 287 7.6.2 Waves at an angle to the Interface 287 7.6.3 Refraction and Refraction 288

7.7 Multipath Effects 289

7.7.1 Mechanism 289 7.7.2 Multipath Lobing 292 7.7.3 Multipath Fading 293 7.7.4 Multipath Tracking 294 7.7.5 Effects on Imaging 296

7.8 References 297

Chapter 8 Target and Clutter Characteristics 299

8.1 Introduction 299 8.2 Target Cross-Section 299

8.2.1 Cross-section and the Equivalent Sphere 300 8.2.2 Cross-section of Real Targets 300

8.3 Radar Cross-sections (RCS) 301

8.4 RCS of Simple Shapes 302

8.4.1 Flat Plate 302

8.4.2 The Sphere 303 8.4.3 Trihedral Reflector 304 8.4.4 Other Simple Calibration Reflectors 304

8.5 Radar Cross-section of Complex Targets 306

8.5.1 Aircraft 306 8.5.2 Ships 306 8.5.3 Ground Vehicles 309

8.6 Effect of Target Material 311 8.7 RCS of Living Creatures 311

8.7.1 Human Beings 311 8.7.2 Birds 313 8.7.3 Insects 315

8.8 Fluctuations in Radar Cross-section 315

8.8.1 Temporal Fluctuations 315

8.8.2 Spatial Distribution of Cross-section 317

8.9 Radar Stealth 318

8.9.1 Minimizing Detectability 318 8.9.2 Anti-Stealth Technology 320

8.10 Target Cross-section in the Infrared 321 8.11 Acoustic Target Cross-section 324

8.11.1 Target Composition 324 8.11.2 Target Properties 324 8.11.3 Particulate Targets 325 8.11.4 Underwater Targets 325

8.11.4.1 TS of a Sphere 326

8.11.4.2 TS of Other Shapes 326

8.12 Clutter 328

8.12.1 Ground Clutter 328 8.12.2 Spatial Variations 329 8.12.3 Temporal Variations 333 8.12.4 Sea Clutter 335

8.13 Calculating Surface Clutter Backscatter 336 8.14 Calculating Volume Backscatter 338

8.14.1 Rain 339

8.14.2 Dust and Mist Backscatter 339

8.15 Sonar Clutter and Reverberation 342

8.15.1 Backscatter 342

8.15.2 Volume Reverberation 343

8.16 Worked Example: Orepass Radar Development 343

8.16.1 Requirement 343 8.16.2 Selection of a Sensor 344

Table of Contents XIII

8.16.3 8.16.4 8.16.5 8.16.6 8.16.7 8.16.8 8.16.9

16.10 16.11 16.12 16.13 16.14 16.15 16.16 8

Range Resolution 345 Target Characteristics 345 Clutter Characteristics 346 Target Signal-to-Clutter Ratio (SCR) 346 Antenna Size and Radar Frequency 347 Radar Configuration 347 Component Selection 347

8.16.9.1 Antenna Options 347 8.16.9.2 Radar Transmitter 348 8.16.9.3 Receiver Options 349 Signal-to-Noise Ratio 351 Output Signal-to-Noise Ratio 351 Required IF Gain 352

Detection Probability and Pulses Integrated 352 Measurement Update Rate 352 Monitoring Rock Falling Down the Pass 352 Prototype Build and Test 353

8.17 References 355

Chapter 9 Detection of Signals in Noise

9.1 Receiver Noise 357

9.1.1 Radar Noise 357 9.1.2 Noise Probability Density Functions 359 9.1.3 Infrared Detection and Lidar Noise 359

9.1.3.1 Thermal Noise 359 9.1.3.2 Shot Noise 360 9.1.3.3 Avalanche Noise 361 9.1.3.4 1/f Noise 361 9.1.3.5 Total Noise Contribution 361

9.1.4 Sonar Noise 361

9.1.4.1 Thermal Noise 361

9.1.4.2 Noise from the Sea 362

9.2 Effects of Signal-to-noise Ratio 362

9.2.1 Probability of False Alarm 362 9.2.2 Example 364 9.2.3 Probability of Detection 364 9.2.4 Detector Loss Relative to an Ideal System 368

9.3 The Matched Filter 369 9.4 Coherent Detection 370 9.5 Integration of Pulse Trains 371 9.6 Detection of Fluctuating Signals 373 9.7 Detecting Targets in Clutter 376

357

XIV Table of Contents

9.8 Constant False Alarm Rate (CFAR) Processors 377 9.9 Target Detection Analysis 379

9.9.1 Worked Example: Target Detection with Air Surveillance Radar 380

9.9.1.1 Determine Receiver Parameters 381 9.9.1.2 Radar Range Equation 382 9.9.1.3 Determine the Receiver Noise and

SNR 382 9.9.1.4 Solve for the Detection Range (m) 383

9.9.2 Range Analysis Software Packages 385

9.9.3 Detection Range in Rain 385

9.10 Noise Jamming 387

9.10.1 Noise Jamming Example 388

9.11 References 388

Chapter 10 Doppler Measurement 389

10.1 The Doppler Shift 389

10.1.1 Doppler Shift Derivation 389

10.2 Doppler Geometry 392

10.2.1 Targets moving at low velocities (v « c) 392

10.2.2 Targets Moving at High Speed (v < c) 392

10.3 Doppler Shift Extraction 393

10.3.1 Direction Discrimination 394 10.3.1.1 Sideband Filtering 395 10.3.1.2 Offset Carrier Demodulation 395 10.3.1.3 In-phase/Quadrature

Demodulation 396

10.4 Pulsed Doppler 398 10.5 Doppler Sensors 403

10.5.1 Continuous Wave Doppler Ultrasound 403 10.5.2 Continuous Wave Doppler Radar 404

10.5.2.1 Intruder Detection 404 10.5.2.2 Sports Radar 406 10.5.2.3 Police Radar Speed Trap 407 10.5.2.4 Worked Example: Police Radar and

Detector Comparison 407 10.5.2.5 Projectile Tracking Radar 411 10.5.2.6 Doppler Target Identification 412

10.5.3 Pulsed Doppler Ultrasound 413 10.5.4 Pulsed Doppler Radar 414

10.6 Doppler Target Generator 416

Table of Contents xv

10.7 Case Study: Estimating the Speed of Radio Controlled Aircraft 417

10.7.1 Background 418 10.7.2 Measured Data 420

10.8 References 423

Chapter 11 High Range-Resolution Techniques 425

11.1 Classical Modulation Techniques 425

11.2 Amplitude Modulation 425

11.2.1 Range Resolution 42 5

11.3 Frequency & Phase Modulation 427

11.3.1 Matched Filter 427

11.4 Phase-Coded Pulse Compression 430

11.4.1 Barker Codes 431

11.4.2 Random Codes 432

11.4.2.1 Optimal Binary Sequences 433

11.4.3 Correlation 436

11.4.3.1 Binary Correlation 436 11.4.3.2 Circular Correlation 436

11.5 SAW Based Pulse Compression 437 11.6 Step Frequency 439 11.7 Frequency-modulated continuous-wave Radar 442

11.7.1 Operational Principles 442 11.7.2 Matched Filtering 445 11.7.3 The Ambiguity Function 446 11.7.4 Effect of a Non-Linear Chirp 449 11.7.5 Chirp Linearization 450

11.7.5.1 Open Loop Techniques 450 11.7.5.2 Determining the Effectiveness of Linearization

Techniques 450 11.7.5.3 Implementation of Closed-Loop

Linearization 451 11.7.5.4 Direct Digital Synthesis 453

11.7.6 Extraction of Range Information and Range Gating 454

11.7.6.1 FFT Processing 454

11.7.6.2 Other Range Gating Methods 455

11.7.7 Problems with FMCW 455

11.8 Stretch 455 11.9 Interrupted FMCW 456

11.9.1 Disadvantages 456 11.9.2 Optimizing for a Long Range Imaging Application 458 11.9.3 Implementation 458

XVI Table of Contents

11.10 Sidelobes and Weighting for Linear FM Systems 459 11.11 High Resolution Radar Systems 461

11.11.1 Industry 461 11.11.2 Automotive Radar 462 11.11.3 Research Radars 464

11.12 Worked Example: Brimstone Antitank Missile 464

11.12.1 System Specifications 465 11.12.2 Seeker Specifications (known) 466 11.12.3 Operational procedure—Lock-on after launch 467 11.12.4 System Performance (speculated) 467

11.12.4.1 Target Detection and Identification 467 11.12.4.2 Radar Front End 468 11.12.4.3 Antenna and Scanner 469 11.12.4.4 Signal Processing 471 11.12.4.5 Signal-to-Clutter Ratio: Clutter Levels 471 11.12.4.6 Target Levels 473 11.12.4.7 Signal-to-Clutter Ratio 473 11.12.4.8 Signal-to-Noise Ratio 474 11.12.4.9 Target Identification: Doppler Processing 475 11.12.4.10 Target Identification: Other Techniques 476

11.12.5 Tracking and Guidance 476

11.13 References 477

Chapter 12 High Angular-Resolution Techniques 481

12.1 Introduction 481 12.2 Phased Arrays 482

12.2.1 Advantages of using Phased Arrays 482 12.2.2 Array Synthesis 483 12.2.3 Two Point Array 486 12.2.4 4 Point Array 487 12.2.5 The General Case 488

12.3 The Radiation Pattern 489

12.3.1 Linear Array 489

12.3.2 Radiation pattern: 2D Rectangular Array 490

12.4 Beam Steering 491

12.4.1 Active and Passive Arrays 493

12.4.2 Corrections to Improve Range Resolution 493

12.5 Array Characteristics 494

12.5.1 Antenna Gain and Beamwidth 494 12.5.2 Matching and Mutual Coupling 494 12.5.3 Thinned arrays 494 12.5.4 Conformal Arrays 495

Table of Contents XVII

12.6 Applications 495

12.6.1 Acoustic Array 496 12.6.2 New Generation MMIC Phased Arrays 496 12.6.3 Early Warning Phased Array Radar 496

12.7 Sidescan Sonar 500

12.7.1 Operational Principles 500 12.7.2 Hardware 501 12.7.3 Operation and Image Interpretation 502 12.7.4 Signal Processing 504

12.8 Worked Example: Performance of the ICT-5202 Transducer 506 12.9 Doppler Beam-Sharpening 513 12.10 Operational Principles of Synthetic Aperture 516 12.11 Range and Cross-range Resolution 517

12.11.1 Unfocused SAR 517 12.11.2 Focused SAR 519 12.11.3 Resolution Comparison 522

12.12 Worked Example: Synthetic Aperture Sonar 522 12.13 Radar Image Quality Issues 527

12.13.1 Perspective of a Radar Image 527 12.13.2 Image Distortion 528

12.13.2.1 Stretching 528

12.13.2.2 Shadowing 528

12.13.3 Speckle 528

12.14 SAR on Unmanned Aerial Vehicles 528

12.14.1 TESAR 528 12.14.2 MiniSAR 530

12.15 Airborne SAR Capability 5 3 2

12.16 Space-based SAR 533

12.16.1 Interferometry 535

12.17 Magellan Mission to Venus 536 12.18 References 537

Chapter 13 Range and Angle Estimation and Tracking 539

13.1 Introduction 539

13.2 Range Estimation and Tracking 539

13.2.1 Range Gating 539

13.3 Principles of a Split-Gate Tracker 540

13.3.1 Range Transfer Function 540

13.3.2 Noise on Split-Gate Trackers 541

13.4 Range Tracking Loop Implementation 542

13.4.1 The A-ß Filter 543

XVIII Table of Contents

13.4.2 The Kaiman Filter 545 13.4.3 Other Tracking Filters 545

13.5 Ultrasonic Range Tracker Example 546 13.6 Tracking Noise after Filtering 546 13.7 Tracking Lag for an Accelerating Target 550 13.8 Worked Example: Range Tracker Bandwidth Optimization 551

13.9 Range Tracking Systems 553

13.9.1 Lidar Speed Trap 553

13.10 Seduction Jamming 555 13.11 Angle Measurement 557

13.11.1 Amplitude Thresholding 557

13.11.2 Proximity Detector Example 558

13.12 Angle Tracking Principles 558

13.12.1 Scanning Across the Target 558

13.12.2 Null Steering 559

13.13 Lobe Switching (Sequential Lobing) 559

13.13.1 Main Disadvantages of Lobe Switching 560

13.14 Conical Scan 560 13.14.1 The Squint Angle Optimization Process 563 13.14.2 Measuring the Conscan Antenna Transfer

Function 563 13.14.3 Application 564 13.14.4 Main Disadvantages 566 13.14.5 Other considerations 567

13.15 Infrared Target Trackers 567 13.16 Amplitude Comparison Monopulse 568

13.16.1 Antenna Patterns 568 13.16.2 Generation of Error Signals 568

13.17 Comparison between Conscan and Monopulse 571 13.18 Angle Tracking Loops 573

13.19 Angle Estimation and Tracking Applications 574

13.19.1 Instrument Landing System (ILS) 574

13.19.1.1 Localizer Transmitter 574 13.19.1.2 Localizer Receiver 575

13.19.1.3 Glide Slope Equipment 575

13.20 Worked Example: Combined Acoustic and Infrared Tracker 575

13.20.1 Operational Principles of Prototype 576 13.20.2 Theoretical Performance 579 13.20.3 Tracker Implementation 581

13.20.3.1 Beacon 581 13.20.3.2 Receiver 582

Table of Contents XIX

13.20.4 Construction 585 13.20.5 Control Algorithms 586

13.21 Angle Track Jamming 586

13.22 Triangulation 587

13.22.1 Loran-C 588

13.22.1.1 Summary of Operation 588 13.22.1.2 Measurement Process 588 13.22.1.3 Advantages of Loran-C 590

13.23 References 591 '

Chapter 14 Tracking Moving Targets 593

14.1 Track While Scan 593 14.2 The Coherent Pulsed Tracking Radar 595

14.2.1 Single Channel Detection 597 14.2.2 I/Q Detection 598 14.2.3 Moving Target Indicator (MTI) 598

14.2.3.1 Blind Speeds 601 14.2.3.2 Staggered PRF and Blind Speed 602

14.3 Limitations to MTI Performance 603 14.4 Range-Gated Pulsed Doppler Tracking 603 14.5 Coordinate Frames 605

14.5.1 Measurement Frame 605 14.5.2 Tracking and Estimation Frame 605

14.6 Antenna Mounts and Servo Systems 606 14.7 On-Axis Tracking 608

14.7.1 Crossing Targets and Apparent Acceleration 608 14.7.2 Millimeter Wave Tracking Radar 616

14.8 Tracking in Cartesian Space 619 14.9 Worked Example: Fire Control Radar 620

14.9.1 Requirements 621 14.9.2 Selection of Polarization 621 14.9.3 Positioner Specifications 622 14.9.4 Radar Horizon 622 14.9.5 Selection of Frequency 623 14.9.6 Adverse Weather Effects 623 14.9.7 Required Single Pulse Signal-to-Noise Ratio 624 14.9.8 Tracking Gate Size 626 14.9.9 Signal-to-Clutter 626 14.9.10 Moving Target Indicator 627 14.9.11 The Pulse Repetition Frequency 627 14.9.12 Search Requirement 628 14.9.13 Integration Gain 630

XX Table of Contents

14.9.14 Matched Filter 630 14.9.15 Transmitter Power 631 14.9.16 System Configuration 631 14.9.17 Free Space Detection Range 632 14.9.18 Effects of Multipath on Aircraft Detection 634 14.9.19 Detection Threshold and CFAR 636 14.9.20 Transition to Track 637

14.9.21 Target Tracking 637

14.10 References 640

Chapter 15 Radio Frequency Identification Tags and Transponders 641

15.1 Principle of Operation 641 15.2 History 641 15.3 Secondary Surveillance Radar 642

15.3.1 Interrogation Equipment 643 15.3.2 Transponder Equipment 643 15.3.3 Operation 643 15.3.4 SSR Issues 644

15.3.4.1 Sidelobe problems 644

15.3.4.2 Congestion 645

15.4 Radio Frequency Identification (RFID) Systems 646

15.4.1 Electronic Article Surveillance (EAS) 647

15.4.1.1 Radio Frequency Tags 647 15.4.1.2 Acousto-Magnetic Tags 647 15.4.1.3 Microwave Tags (E-tags) 648

15.4.2 Multibit EAS Tags 649

15.4.3 Magnetic Coupled RFID Transponder Systems 649

15.4.3.1 Operational Principles 649

15.4.4 Electromagnetic Coupled RFID Transponder Systems 650

15.5 Other Applications 652

15.5.1 House Arrest Tag 652

15.6 Social Issues 653 15.7 Technical Challenges 654 15.8 Harmonic Radar 655

15.9 Battlefield Combat ID System (BCIS) 655

15.9.1 Combat Identification: The Future 656

15.10 References 657

Chapter 16 Tomography and 3D Imaging 659

16.1 Principle of Operation 659 16.2 CT Imaging 660

16.2.1 Image Reconstruction 662

Table of Contents XXI

16.2.2 What is displayed in CT images 664 16.2.3 Two Dimensional Displays 665 16.2.4 Three Dimensional Displays 665

16.3 Magnetic Resonance Imaging (MRI) 665

16.3.1 Nuclear Magnetic Resonance (NMR) 667 16.3.2 Imaging Process 670 16.3.3 Imaging Resolution 673

16.4 MRI Images 673 16.5 Functional MRI Investigations of Brain Function 673 16.6 Positron Emission Tomography 674

16.6.1 Examples of the use of PET Scans 677

16.7 3D Ultrasound Imaging 677

16.7.1 2D Medical Ultrasound 677

16.7.1.1 Medical Applications 680

16.7.1.2 Dangers of Ultrasound Use 680

16.8 3D Extension 680

16.8.1 Ultrasonic Computed Tomography 682

16.9 3D Sonar Imaging 683

16.10 Ground Penetrating Radar 686

16.10.1 3D Imaging using GPR 690

16.11 Worked Example: Detecting a Ruby Nodule in a Rock Matrix 691 16.12 References 693

Index 695