Preface xi

Nomenclature and Abbreviations xiii

Chapter 1 Introduction to Radiometry / 1

1.1 Definitions 1

1.2 Why Measure Light? 2

1.3 Historical Background 4

1.4 Radiometric Measurement Process 5

1.5 Radiometry Applications 7

References 9

Chapter 2 Propagation of Optical Radiation / 11

2.1 Basic Definitions 11

    2.1.1 Rays and angles 11

    2.1.2 System parameters 19

    2.1.3 Optical definitions 23

2.2 Fundamental Radiometric Quantities 24

    2.2.1 Radiance 24

    2.2.2 Radiant exitance 26

    2.2.3 Irradiance 28

    2.2.4 Radiant intensity 29

2.3 Radiometric Approximations 30

    2.3.1 Inverse square law 30

    2.3.2 Cosine³ law 31

    2.3.3 Lambertian approximation 32

    2.3.4 Cosine⁴ law 33

2.4 Equation of Radiative Transfer 36

2.5 Configuration Factors 38

2.6 Effect of Lenses on Power Transfer 40

2.7 Common Radiative Transfer Configurations 42

    2.7.1 On-axis radiation from a circular Lambertian disc 42

    2.7.2 On-axis radiation from a non-Lambertian disc 43

    2.7.3 On-axis radiation from a spherical Lambertian source 44

2.8 Integrating Sphere 46

2.9 Radiometric Calculation Examples 48

    2.9.1 Intensities of a distant star and the sun 48

    2.9.2 Lunar constant 50

        2.9.2.1 Calculation 50

        2.9.2.2 Moon-sun comparisons 51

    2.9.3 "Solar furnace" 52

    2.9.4 Image irradiance for finite conjugates 53

    2.9.5 Irradiance of the overcast sky 55

    2.9.6 Near extended source 55

    2.9.7 Projection system 56

2.10 Generalized Expressions for Image-Plane Irradiance 57

    2.10.1 Extended source 57

    2.10.2 Point source 58

2.11 Summary of Some Key Concepts 58

For Further Reading 59

References 59

Chapter 3 Radiometric Properties of Materials / 61

3.1 Introduction and Terminology 61

3.2 Transmission 62

3.3 Reflection 63

3.4 Absorption 69

3.5 Relationship Between Reflectance, Transmittance, and Absorptance 69

3.6 Directional Characteristics 69

    3.6.1 Specular transmittance and reflectance 69

    3.6.2 Diffuse transmittance and reflectance 73

3.7 Emission 76

3.8 Spectral Characteristics 77

3.9 Optical Materials Checklist 79

For Further Reading 80

References 80

Chapter 4 Generation of Optical Radiation / 83

4.1 Introduction 83

4.2 Radiation Laws 84

    4.2.1 Planck's law 84

    4.2.2 Wien displacement law 86

    4.2.3 Stefan-Boltzmann law 89

    4.2.4 Laws in photons 89

    4.2.5 Rayleigh-Jeans law 92

    4.2.6 Wien approximation 93

    4.2.7 More on the Planck equation 93

    4.2.8 Kirchhoff's law 97

4.3 Emitter Types and Properties 102

    4.3.1 Metals 102

    4.3.2 Dielectrics 102

    4.3.3 Gases 103

4.4 Practical Sources of Radiant Energy 104

    4.4.1 Two major categories 104

    4.4.2 Thermal sources 105

        4.4.2.1 Tungsten and tungsten-halogen lamps 105

        4.4.2.2 Other metallic sources 108

        4.4.2.3 Dielectric thermal sources 108

        4.4.2.4 Optical elements 109

        4.4.2.5 Miscellaneous thermal sources 109

    4.4.3 Luminescent sources 110

        4.4.3.1 General principles 110

        4.4.3.2 Fluorescent lamps 116

        4.4.3.3 Electroluminescent sources 118

        4.4.3.4 LED sources 118

        4.4.3.5 Lasers 119

    4.4.4 Natural sources 120

        4.4.4.1 Sunlight 120

        4.4.4.2 Skylight, planetary, and astronomical sources 121

        4.4.4.3 Application: energy balance of the earth 122

4.5 Radiation Source Selection Criteria 122

4.6 Source Safety Considerations 124

4.7 Summary of Some Key Concepts 124

For Further Reading 124

References 125

Chapter 5 Detectors of Optical Radiation / 127

5.1 Introduction 127

5.2 Definitions 128

5.3 Figures of Merit 131

5.4 #N$O%&I*S@E~^ 133

    5.4.1 Introduction to noise concepts 133

    5.4.2 Effective noise bandwidth 136

    5.4.3 Catalog of most unpleasant noises 137

        5.4.3.1 Johnson noise 137

        5.4.3.2 Shot noise 139

        5.4.3.3 1/f noise 139

        5.4.3.4 Generation-recombination noise 140

        5.4.3.5 Temperature fluctuation noise 141

        5.4.3.6 Photon noise 141

        5.4.3.7 Microphonic noise 142

        5.4.3.8 Triboelectric noise 142

        5.4.3.9 CCD noises 142

        5.4.3.10 Amplifier noise 143

        5.4.3.11 Quantization noise 143

    5.4.4 Noise factor, noise figure, and noise temperature 143

    5.4.5 Some noise examples 144

    5.4.6 Computer simulation of Gaussian noise 147

5.5 Thermal Detectors 147

    5.5.1 Thermal circuit 147

    5.5.2 Thermoelectric detectors 150

        5.5.2.1 Basic principles 150

        5.5.2.2 Combinations and configurations 153

    5.5.3 Thermoresistive detector: bolometer 155

    5.5.4 Pyroelectric detectors 157

        5.5.4.1 Basic principles 157

        5.5.4.2 Pyroelectric materials 160

        5.5.4.3 Operational characteristics of pyroelectric detectors 162

        5.5.4.4 Applications of pyroelectric detectors 162

    5.5.5 Other thermal detectors 163

5.6 Photon Detectors 164

    5.6.1 Detector materials 164

    5.6.2 Photoconductive detectors 169

        5.6.2.1 Basic principles 169

        5.6.2.2 Noises in photoconductive detectors 173

        5.6.2.3 Characteristics of photoconductive detectors 174

        5.6.2.4 Applications of photoconductive detectors 175

    5.6.3 Photoemissive detectors 175

        5.6.3.1 Basic principles 175

        5.6.3.2 Classes of emitters 176

        5.6.3.3 Dark current 181

        5.6.3.4 Noises in photoemissive detectors 182

        5.6.3.5 Photoemissive detector types 183

    5.6.4 Photovoltaic detectors 185

        5.6.4.1 Basic principles 185

        5.6.4.2 Responsivity and quantum efficiency 195

        5.6.4.3 Noises in photovoltaic detectors 196

        5.6.4.4 Photovoltaic detector materials and configurations 198

5.7 Imaging Arrays 199

    5.7.1 Introduction 199

    5.7.2 Photographic film 199

        5.7.2.1 History 199

        5.7.2.2 Physical characteristics 201

        5.7.2.3 Spectral sensitivity 201

        5.7.2.4 Radiometric calibration 201

        5.7.2.5 Spatial resolution 202

        5.7.2.6 Summary 202

    5.7.3 Electronic detector arrays 203

        5.7.3.1 History 203

        5.7.3.2 Device architecture description and tradeoffs 203

        5.7.3.3 Readout mechanisms 204

        5.7.3.4 Comparison 207

    5.7.4 Three-color CCDs 207

    5.7.5 Ultraviolet photon-detector arrays 208

    5.7.6 Infrared photodetector arrays 209

    5.7.7 Uncooled thermal imagers 210

    5.7.8 Summary 211

For Further Reading 211

References 213

Chapter 6 Radiometric Instrumentation / 215

6.1 Introduction 215

6.2 Instrumentation Requirements 215

    6.2.1 Ideal radiometer 215

    6.2.2 Specification sheet 215

    6.2.3 Spectral considerations 216

    6.2.4 Spatial considerations 217

    6.2.5 Temporal considerations 217

    6.2.6 Make or buy? 218

6.3 Radiometer Optics 218

    6.3.1 Introduction 218

    6.3.2 Review of stops and pupils 218

    6.3.3 The simplest radiometer: bare detector 219

    6.3.4 Added aperture 219

    6.3.5 Basic radiometer 221

    6.3.6 Improved radiometer 223

    6.3.7 Other methods for defining the field of view 224

    6.3.8 Viewing methods 224

    6.3.9 Reference sources 226

    6.3.10 Choppers 226

    6.3.11 Stray light 227

    6.3.12 Summing up 228

6.4 Spectral Instruments 228

    6.4.1 Introduction 228

    6.4.2 Prisms and gratings 230

    6.4.3 Monochromator configurations 231

    6.4.4 Spectrometers 234

    6.4.5 Additive versus subtractive dispersion 235

    6.4.6 Arrays 236

    6.4.7 Multiple slit systems 236

    6.4.8 Filters 236

    6.4.9 Interferometers 237

    6.4.10 Fourier transform infrared 237

    6.4.11 Fabry-Perot 238

For Further Reading 240

References 240

Chapter 7 Radiometric Measurement and Calibration / 241

7.1 Introduction 241

7.2 Measurement Types 241

7.3 Errors in Measurements, Effects of Noise, and Signal-to-Noise Ratio in Measurements 241

7.4 Measurement and Range Equations 250

7.5 Introduction to the Philosophy of Calibration 253

7.6 Radiometric Calibration Configurations 257

    7.6.1 Introduction 257

    7.6.2 Distant small source 258

    7.6.3 Distant extended source 260

    7.6.4 Near extended source 261

    7.6.5 Near small source 262

    7.6.6 Direct method 262

    7.6.7 Conclusion 263

7.7 Example Calculations: Satellite Electro-optical System 263

7.8 Final Thoughts 267

For Further Reading 268

References 268

Table of Appendices / 269

Appendix A: Systeme Internationale (SI) Units for Radiometry and Photometry 271

Appendix B: Physical Constants, Conversion Factors, and Other Useful Quantities 275

Appendix C: Antiquarian's Garden of Sane and Outrageous Terminology 277

Appendix D: Solid-Angle Relationships 283

Appendix E: Glossary 285

Appendix F: Effective Noise Bandwidth of RC Filters and the Selection of Filter Parameters to Optimize Signal-to-Noise Ratio 297

Appendix G: Bandwidth Normalization by Moments 305

Appendix H: Jones Near-Small-Source Calibration Configuration 309

Appendix I: Is Sunglint Observable in the Thermal Infrared? 313

Appendix J: Documentary Standards for Radiometry and Photometry 321

Appendix K: Radiometry and Photometry Bibliography 341

Appendix L: Reference List for Noise and Postdetection Signal Processing 357

Index / 361

Foreword

The material for this book grew out of a first-year graduate-level course, "Radiometry, Sources, Materials, and Detectors," that Jim Palmer created and taught at the University of Arizona College of Optical Sciences for many years. The book is organized by topic in a similar manner, with the first five chapters presenting radiation propagation and system building blocks, and the final two chapters focusing on instruments and their uses. Chapter 1 provides an overview and history of the subject, and Chapter 2 presents basic concepts of radiometry, including terminology, laws, and approximations. It also includes examples that will allow the reader to see how key equations may be used to address problems in radiation propagation. Chapter 3 introduces radiometric properties of materials such as reflection and absorption, and Chapter 4 extends that discussion via a detailed consideration of sources. Point and area detectors of optical radiation are considered in Chapter 5, which also includes thermal and photon detection mechanisms, imaging arrays, and a discussion about film.

In Chapter 6, the focus shifts to instrumentation. Concepts introduced in Chapter 2 are here applied to instrument design. Practical considerations relating to radiometer selection are detailed, and a "Make or Buy?" decision is explored. Several monochromator configurations are examined, and spectral instruments are discussed. Proceeding from instruments to their uses, Chapter 7 details types of measurements that may be made with radiometric systems and provides a discussion of measurement error. The philosophy of calibration is introduced, and several radiometric calibration configurations are considered.

The material in the appendices covers a variety of topics, including terminology, standards, and discussions of specific issues such as Jones source calibration and consideration of solar glint. Due to Jim's attention to detail and the length of time over which he accumulated material, the long lists he provided here may be viewed as comprehensive, if not current by today's standards.

The level of discussion of the material is suitable for a class taught to advanced undergraduate students or graduate students. The book will also be useful to the many professionals currently practicing in fields in which radiometry plays a part: optical engineering, electro-optical engineering, imagery analysis, and many others.

In 2006, Jim Palmer was told that he was terminally ill, and he asked me to complete this work. I was humbled and honored by the request. I'd met Jim as a graduate student in optical sciences in the late 1980s, and he had served on my thesis committee. My career after graduation had focused on systems engineering and analysis, two areas in which radiometry plays a significant role. For nearly the last ten years of Jim's life, I'd been able to receive mentoring from the master simply by showing up at Jim's office door with a question or topic for discussion, but I never anticipated that our discussions would one day come to an end. Upon Jim's death, I sought to weave his collection of resources and narrative together with newer material and discussion in a manner I hope will be both informative to read and valuable to reference. The preface that follows was written by Jim before he died and has been left as he wrote it.

I am grateful for the assistance of many. First is William L. Wolfe, Jim's professor and mentor, who offered helpful comments on each chapter and adapted Chapter 6 on radiometric instrumentation. Others for whose help I am grateful, all from or associated with the University of Arizona College of Optical Sciences, are Bob Schowengerdt, who contributed the narrative on film; Anurag Gupta of Optical Research Associates, Tucson, Arizona, who adapted the appendix material; and L. Stephen Bell, Jim's close friend and colleague, who revised the signal processing discussion that appears in that section and provided a complete bibliography on the subject. A special note of thanks goes to Eustace Dereniak, who provided office space for me, helpful discussions, and hearty doses of encouragement. I also wish to thank John Reagan, Kurt Thome (NASA Goddard Spaceflight Center, Greenbelt, Maryland), Mike Nofziger, and Arvind Marathay for review, discussion, and helpful insights. In addition, I am grateful for the assistance of Anne Palmer, Jim's beloved sister, and University of Arizona College of Optical Sciences staff members Trish Pettijohn and Ashley Bidegain. Gwen Weerts and Tim Lamkins of SPIE Press have my gratitude for the special assistance they provided to this project. I also gratefully acknowledge Philip N. Slater, my professor in optical sciences, who selected me as a graduate student and trained me in remote sensing and absolute radiometric calibration from 1987 to 1989, and Michael W. Munn, formerly Chief Scientist at Lockheed Martin Corporation, who instilled the value of a systems perspective in the approach to technical problems.

Finally, I am grateful to my family for providing financial support; to Ralph Gonzales, Arizona Department of Transportation, and Sylvia Rogers Gibbons for providing professional contacts; and my friends at Calvary Chapel, Tucson, Arizona, whose donations and prayers sustained me as I worked to complete this book.

Barbara G. Grant
Cupertino, California
October 2009

Preface

This volume is the result of nearly twenty years of frustration in locating suitable material for teaching the subject of radiometry and its allied arts. This is not to say that there is not a lot of good stuff out there- it's just not all in one place, consistent in usage of units, and applicable as both a teaching tool and as a reference. I intend this book to be all things to all people interested in radiometry. The material comes from teaching both undergraduate and graduate-level courses at the Optical Sciences Center of the University of Arizona, and from courses developed for SPIE and for industrial clients. I have unabashedly borrowed the tenor of the title from the superb text The Art of Electronics by Paul Horowitz in the hope that this volume will be as useful to the inquisitive reader.

I gratefully acknowledge the contributions of my mentor, William L. Wolfe, Jr., and the hundreds of students whose constant criticism and occasional faint praise have helped immeasurably.

This book is dedicated to the memory of my mother, Candace W. Palmer (1904-1996) and my father, James A. Palmer (1905-1990). She was all one could wish for in a Mom, and he showed me the path to engineering.

James M. Palmer
1937-2007