Spie Press BookAlien Vision: Exploring the Electromagnetic Spectrum with Imaging Technology
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Austin Richards takes readers on a visual tour of the electromagnetic spectrum beyond the range of human sight, using imaging technology as the means to 'see' invisible light. Dozens of colorful images and clear, concise descriptions make this an intriguing, accessible technical book. Richards explains the light spectrum, including visible light, and describes the advanced imaging technologies that enable humans to synthesize our own version of 'alien' vision at different wavelengths, with applications ranging from fire fighting and law enforcement to botany and medicine.
"This clearly written, humorous and outstandingly illustrated non-technical tour of the spectrum of light, from gamma rays to radio waves, is quite enlightening and a pleasure to read."
--J. C. Rosenberg, OPN July 2003
- List of Figures / vii
- Preface / xi
- Introduction / xiii
- 1 Infrared and Ultraviolet: The Edges of the Rainbow / 1
- Night Vision and Surveillance with Near-IR Imaging / 6
- Forensic Imaging with Near-IR and Near-UV Imaging / 10
- Animal Ultraviolet Vision / 19
- Optical Properties of Materials in the Near-IR and Near-UV / 21
- Infrared Photography and Heat Detection / 27
- 2 Thermal Imaging: We All Glow in the Dark / 31
- Midwave and Longwave IR Imaging Systems / 37
- Surveillance and Law Enforcement / 39
- Thermography / 42
- Thermal Imaging and Biology / 45
- Thermal Imaging in Astronomy / 48
- 3 Microwave and Millimeter-Wave Imaging: Piercing the Veil / 51
- Sub-Millimeter-Wave Imaging: T-Rays / 53
- Millimeter-Wave Imaging: Seeing through Clothing and Fog / 55
- Radio Astronomy: The Foundations of Microwave Imaging / 58
- Radar Imaging: A Microwave Searchlight / 64
- Small-Scale Imaging Radar / 71
- 4 X Rays and Gamma Rays: Crookes Tubes and Nuclear Light / 77
- High-Energy Astronomy / 93
- Gamma-Ray Imaging / 96
- PET Scans: Observing Living Tissue with Gamma Rays / 98
- 5 Acoustic Imaging: Seeing with Sound /107
- Underwater Acoustic Imaging / 108
- Ultrasound Medical Imaging /111
- Acoustic Daylight Imaging / 114
- Acoustic Imaging of Sound Sources / 117
- 6 Sweeping through the Spectrum: Comparative Imagery / 123
- Milky Way Images from Radio to Gamma Ray / 128
- Milky Way Image Descriptions / 128
- Epilogue /133
- Glossary / 135
- Bibliography and Internet Resources / 145
- Index / 149
The inspiration for Alien Vision came from two other illustrated science books that I have long admired. Both are visual explorations of nature that use imaging technology to transcend the limitations of human visual perception. The first is The Powers of Ten, by Phillip and Phylis Morrison 1 , which takes the reader on a pictorial journey through 40 powers of ten in size scale, starting with a one-meter square image of a couple sleeping on a park lawn. Each successive section of the book changes the size of the image by a factor of ten, zooming out to view the park, then Chicago, then Lake Michigan, then North America, then Earth; and so on, until finally the square image is so large that it encompasses a multitude of galaxies. Then the "camera" zooms in on the man's hand, on a mosquito feeding there, then on bacteria on the mosquito, and so on, stopping at the sub-atomic particles whirling around in the nucleus of a single atom. There is also a movie version of this book available that includes a sequence where the observer rushes in from viewing distant clusters of galaxies to the hand of the sleeping man!2 The Powers of Ten explores nature in the scale domain, exploring size scales that are much larger and much smaller than the size scale of human visual perception.
The second book is Stopping Time-The Photographs of Harold Edgerton.3 The photographs in this book show commonplace events captured with high-speed cameras using electronic flash units and special shutters invented by Professor Edgerton and his colleagues at the Massachusetts Institute of Technology. Events that happen in thousandths or millionths of a second are captured on film: a bullet passing through an apple, the first atomic bomb test an instant after detonation,a football player kicking a football. The work of Edgerton is an exploration of images of the world in the time domain. The Eames Office, makers of the film version of The Powers of Ten, have also produced a film called The Powers of Time 4 which explores the universe in 37 orders of magnitude of time, from the tiny attosecond to 31 billion years. These time scales are much shorter and much longer than the time scale of human visual perception.
My idea was to apply this same idea of a visual exploration of the universe to the electromagnetic spectrum itself, which could be considered the domain of wavelength. Instead of exploring the universe in many size or time scales, my book would take the reader on a tour of all the possible "colors" of light, from long-wavelength radio waves to extremely short gamma rays. These are wavelengths of light that are much longer and much shorter than the narrow wave-length range of human visual perception. It would be as though the readers had a knob on their heads that they could tune like a radio dial and change the "color response" of their eyes out of the visible spectrum and into the infrared, ultraviolet, and beyond. I worked for a time as an astronomer, and was always fascinated by the way we observe the sky with instrumentation that extends the human visual sense into new realms of the electromagnetic spectrum beyond the visible portion. An astronomy teacher of mine once remarked that if our eyes could only detect radio waves instead of what we call visible light, then we would not see the stars at all. Instead, we would see a sky full of big clouds and swirls of cold interstellar gas, with compact radio sources sprinkled throughout. The familiar night sky we see is only one of many possible skies overlaid on top of one another. I wondered if hypothetical aliens on some distant planet might see a radio sky with their peculiar visual apparatus. Aliens aside, with imaging technology we have the ability to synthesize our own version of "alien vision."
This book is not intended as a comprehensive survey of imaging technology. Rather, it is a compilation of images and descriptions of imaging technology that conveys a sense of what nature looks like when imaged with "invisible light." Descriptions of the imaging technology (electronic sensors and photographic film) are nontechnical in nature, and I include pictures of actual imaging devices only in cases where the layperson can appreciate the design of the device. I have attempted to include a visible-light picture of the same scene or object next to every "invisible light" image, but these visible-light counterparts were not always available.
The majority of the research for this book was carried out through World Wide Web searches, which uncovered many images and articles on imaging. I located the authors of this Web content, and these helpful colleagues transmitted additional articles and digital images to me via e-mail from all over the world. I obtained many of the infrared images in Chapter 2 using cameras provided by my present employer, Indigo Systems Corporation in Santa Barbara, California. I have attempted to obtain the highest-resolution images available, but many of the electronic sensors used to image in invisible wavebands of light have limited resolution, and the resulting images can appear quite grainy in comparison with their visible-light counterparts. In some cases, the ultimate resolution of an image is limited by the wavelike properties of light, properties that make it impossible to resolve features that are smaller than a wavelength. I have used metric units throughout, and terms or jargon in boldface are included in a glossary at the end of the book.