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E-raamat: Thermal Imaging Cameras: Characteristics and Performance

(Bromley, Kent, UK)
  • Formaat: 238 pages
  • Ilmumisaeg: 01-Apr-2009
  • Kirjastus: CRC Press Inc
  • Keel: eng
  • ISBN-13: 9781420071863
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  • Formaat: 238 pages
  • Ilmumisaeg: 01-Apr-2009
  • Kirjastus: CRC Press Inc
  • Keel: eng
  • ISBN-13: 9781420071863
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Intended for suppliers and users of thermal imagers, this guide explains how a thermal imager works, the components it uses, and procedures for measuring several performance characteristics. The performance parameter sections cover field of view, modulation transfer function, and minimum resolvable temperature difference, as well as less common parameters, such as slit response function, narcissus, and scene influence factor. The last two chapters discuss calibration and alignment of test facilities, industrial applications, and specialty applications. Black and white photographs of the different devices are provided. Annotation ©2009 Book News, Inc., Portland, OR (booknews.com)

The ability to see through smoke and mist and the ability to use the variances in temperature to differentiate between targets and their backgrounds are invaluable in military applications and have become major motivators for the further development of thermal imagers. As the potential of thermal imaging is more clearly understood and the cost decreases, the number of industrial and civil applications being exploited is growing quickly. In order to evaluate the suitability of particular thermal imaging cameras for particular applications, it is important to have the means to specify and measure meaningful performance characteristics.

Thermal Imaging Cameras: Characteristics and Performance expands our current understanding of thermal imaging and, most importantly, provides a sound quantitative basis for evaluating the suitability of various thermal imagers for particular applications. Utilizing a practical approach that keeps theory and mathematics to a minimum, the text reviews the important performance parameters for industrial, laboratory, and surveillance applications as well as how these parameters can be measured. The author, T. L. Williams, a distinguished expert on designing and testing thermal imaging systems and recipient of the Callendar Medal from the Institute of Measurement and Control, focuses on the standard form of imaging camera but also includes descriptions of the different specialized forms of thermal imagers useful to anyone working with these systems.

Providing detailed descriptions of the equipment and techniques that can be used for testing complete thermal imagers as well as in the testing of the main subunits of a thermal imager, this comprehensive reference will prove invaluable not only to those who use, test, and design thermal imagers, but also to anyone designing equipment or making measurements in the thermal band of wavelengths.

Preface xiii
Author xv
Symbols and Abbreviations xvii
Chapter 1 An Introduction to Thermal Imaging 1
1.1 Aim of This Book
1
1.2 What Is Thermal Imaging?
1
1.3 Atmospheric Transmission
3
1.4 Choice of 3-5 µm or 8-12 µm
4
1.5 Important Factors in the Application of Thermal Imaging
5
1.6 Specifying and Measuring the Performance of a Thermal Imager
5
Chapter 2 Thermal Imaging Cameras and Their Component Parts 7
2.1 A Basic Thermal Imager
7
2.2 Image-Forming Optical System
8
2.3 Windows for Thermal Imaging
14
2.4 Scanning Mechanisms
15
2.5 Radiation Detectors
18
2.5.1 The Basic Detector
18
2.5.2 Photon/Quantum Detectors
19
2.5.3 Thermal Detector Arrays
21
2.5.4 Some Detector Array Configurations
24
2.6 Cooling Detectors
28
2.7 Special Signal Processing and Other Requirements
32
2.7.1 Signal Offset Correction
32
2.7.2 Conversion to Standard Video Format
32
2.8 Displays
32
2.9 Computer and Software
33
References
33
Chapter 3 Industrial and Commercial Thermal Imagers and the Facilities They Provide 35
3.1 Introduction
35
3.2 Thermal Imagers That Measure Actual Temperature
36
3.2.1 Temperature Measurement
36
3.2.2 Emissivity and Atmospheric Absorption
39
3.2.3 Object Dimensions
42
3.2.4 Thermal and Visible Displays
42
3.3 Software Facilities for Industrial Applications
43
3.3.1 General
43
3.3.2 Monitoring Temperatures
43
3.4 Thermal Imagers for Surveillance Types of Application
45
3.4.1 General
45
3.4.2 Military Applications
47
3.4.3 Civil Applications
48
3.5 Imagers Used by Firefighters
48
3.6 Manufacturers' Data Sheets
50
References
52
Chapter 4 Performance Parameters for Components of a Thermal Imager 53
4.1 Introduction
53
4.2 Lenses
53
4.2.1 Focal Length
53
4.2.2 Magnification (M)
54
4.2.3 Numerical Aperture (NA)
55
4.2.4 f/number
56
4.2.5 Transmission
56
4.2.6 Relative Field Irradiance (RFI)
56
4.2.7 Modulation Transfer Function (MTF)
57
4.2.8 Veiling Glare Index (VGI)
59
4.2.9 Narcissus Effect
59
4.2.10 Distortion
60
4.3 Detectors
61
4.3.1 Detective Quantum Efficiency (DQE)
61
4.3.2 RMS Noise
61
4.3.3 Noise Spectrum
62
4.3.4 Noise-Equivalent Power (NEP)
62
4.3.5 D* (D-star)
62
4.3.6 Responsivity
63
4.3.7 Spectral Response
63
4.3.8 Frequency Response
63
4.3.9 Time Constant
63
4.3.10 Modulation Transfer Function (MTF)
64
4.4 Scanners
65
4.4.1 Horizontal Scan Linearity
65
4.4.2 Vertical Scan Linearity
65
4.4.3 Scan Judder
65
4.5 Displays
66
4.5.1 General
66
4.5.2 Maximum Luminance
66
4.5.3 Polar Luminance Distribution
66
4.5.4 Grey Scale/Linearity
66
4.5.5 MTF
67
4.5.6 Distortion
67
4.5.7 Veiling Glare
68
References
69
Chapter 5 Performance Parameters for a Complete Thermal Imager 71
5.1 Introduction
71
5.2 Factors Affecting Performance
71
5.3 Performance Parameters
73
5.3.1 MTF
73
5.3.2 Nyquist Limit
73
5.3.3 Aliasing
74
5.3.4 Signal Transfer Function (SiTF)
75
5.3.5 Noise-Equivalent Temperature Difference (NETD)
76
5.3.6 Minimum Resolvable Temperature Difference (MRTD): The Johnson Criterion
76
5.3.7 Minimum Detectable Temperature Difference (MDTD)
79
5.3.8 Objective MRTD
79
5.3.8.1 MRTD Model A (Video or Display)
80
5.3.8.2 MRTD Model B
81
5.3.9 Objective MDTD
81
5.3.10 Slit Response Function (SRF)
81
5.3.11 Aperture Response Function (ARF)
82
5.3.12 Absolute Temperature Range
82
5.3.13 Maximum and Minimum Temperature Difference Range and Offset Temperature Range
83
5.3.14 Temperature Measurement Uncertainty
83
5.3.15 Emissivity Range
83
5.3.16 Narcissus
83
5.3.17 Veiling Glare Index (VGI) and Uniformity Index (VGUI)
84
5.3.18 Scene Influence Factor (SIF)
84
5.3.19 Field of View (FOV)
85
5.3.20 Close Focus Distance
85
5.3.21 Spectral Response
85
5.4 Frame Rates and Readout Timing
86
5.5 Other Factors
86
References
86
Chapter 6 Basic Equipment for Testing and Calibrating at Thermal Wavelengths 87
6.1 Introduction
87
6.2 Radiation Sources
87
6.2.1 Tungsten Filament Lamps
87
6.2.2 Nichrome Wire or Strip Sources
88
6.2.3 Nernst Glower
89
6.2.4 Globar (SiC/Carborundum Rod)
90
6.2.5 Opperman Source
90
6.2.6 Blackbody
90
6.2.7 High-Emissivity Plates
91
6.2.8 Modulated IR Sources
91
6.2.9 Laser, Laser Diode, and LED Sources
92
6.3 Infrared Detectors
93
6.4 Cooling Detectors
93
6.5 Optical Systems and Collimators
93
6.5.1 General
93
6.5.2 Off-Axis Paraboloid Collimators
93
6.5.3 Multimirror Collimators
96
6.5.4 Refracting Collimators
96
6.5.4.1 3-5 µm Collimators
96
6.5.4.2 8-14 µm Collimators
97
6.5.5 High-Magnification Objectives
97
6.6 Integrating Spheres
97
6.7 Spectral Filters
99
References
101
Chapter 7 Measurement Procedures and Techniques for the Principal Components That Make Up a Thermal Imager 103
7.1 Introduction
103
7.2 General Measurement Procedures
103
7.3 Lenses and Optical Systems
104
7.3.1 Focal Length
104
7.3.2 Angular Magnification
107
7.3.3 f/number or NA
109
7.3.4 Entrance and Exit Pupil Diameters of Afocal Systems
111
7.3.5 Distortion
112
7.3.6 Spectral Transmission
113
7.3.7 Relative Field Irradiance
117
7.3.8 Veiling Glare
118
7.3.9 Narcissus
119
7.3.10 MTF
120
7.3.10.1 Testing Image-Forming Objectives
121
7.3.10.2 Testing Afocal Systems
126
7.3.10.3 Measuring MTF with a Detector Array or Thermal Imager
126
7.3.10.4 Removing a Pedestal or dc Offset from the LSF
127
7.4 Detectors and Detector Arrays
128
7.4.1 Responsivity
128
7.4.2 Detective Quantum Efficiency (DQE)
130
7.4.3 RMS Noise
131
7.4.4 Noise-Equivalent Power (NEP)
131
7.4.5 Frequency Response
131
7.4.6 MTF
132
7.4.6.1 Slit Scan While Monitoring the Output of a Single Element
132
7.4.6.2 Slit and Array Scan Technique for Linear and 2D Arrays
133
7.4.6.3 Tilted (Sloping) Slit Technique for 2D Arrays
134
7.4.6.4 SPRITE or Detector with TDI
135
7.4.6.5 Random Pattern Technique
135
7.4.6.6 Software Requirements
136
7.5 Scanners
136
7.6 Displays
137
7.6.1 Luminance and Spectral Characteristics
137
7.6.2 Polar Luminance Distribution
137
7.6.3 Grey Scale/Linearity
138
7.6.4 MTF
138
7.6.4.1 Eyepiece Displays
140
7.6.5 Distortion
141
7.6.6 Veiling Glare
142
References
143
Chapter 8 Measurement Techniques and Procedures for Complete Thermal Imagers 145
8.1 Introduction
145
8.2 MTF
146
8.2.1 General
146
8.2.2 Measurement from the Video Output
146
8.2.3 Measurement off the Display
147
8.3 Nyquist Limit
148
8.4 Aliasing
148
8.5 Signal Transfer Function (SiTF)
149
8.6 Noise-Equivalent Temperature Difference (NETD)
150
8.7 Minimum Resolvable Temperature Difference (MRTD)
151
8.8 Minimum Detectable Temperature Difference (MDTD)
153
8.9 Objective MRTD
154
8.10 Objective MDTD
154
8.11 Slit Response Function (SRF)
154
8.12 Aperture Response Function (ARF)
155
8.13 Temperature Measurement Performance Characteristics
155
8.14 Emissivity Range
156
8.15 Narcissus
157
8.16 Veiling Glare Index (VGI) and Uniformity Index (VGUI)
157
8.17 Scene Influence Factor (SIF)
158
8.18 Field of View (FOV)
159
8.19 Close Focus Distance
159
8.20 Spectral Response
160
References
162
Chapter 9 Calibration and Alignment of Test Facilities 163
9.1 Introduction
163
9.2 Calibrating and Aligning a Collimator
163
9.2.1 Wavefront Deformation (Aberration)
163
9.2.2 Calibrating Focal Length
165
9.2.3 Collimator Alignment and Focus
166
9.2.4 Test Piece Alignment
170
9.2.4.1 Lens System
170
9.2.4.2 Thermal Imager
171
9.2.5 Checking an MTF Test Facility
172
9.2.5.1 Audit Lenses
172
9.2.5.2 Standard Lenses
172
9.2.5.3 Slits
173
9.2.5.4 Square-Topped Pulses
173
9.3 Radiometric Characteristics
173
9.3.1 General
173
9.3.2 Temperature Sensors
174
9.3.3 Blackbodies
175
9.3.4 Radiometers
175
9.3.5 Radiometric Calibration of an MRTD or Similar Test Facility
178
9.3.6 Spectral Characteristics
179
References
179
Chapter 10 Applications of Thermal Imaging Cameras 181
10.1 Introduction
181
10.2 Industrial Applications
181
10.2.1 Buildings and Structures
181
10.2.2 Inspection of Composite Panels and Structures
182
10.2.3 Inspection of Furnace and Other High-Temperature Constructions
183
10.2.4 Plant and Site Inspection
184
10.3 Advanced and Specialist Applications
186
10.3.1 Detection of Buried Objects
186
10.3.2 Studying and Preserving Works of Art
186
10.3.3 Fire Detection and Volcano Monitoring
187
10.3.4 Visualizing Electric and Magnetic Fields
187
10.3.5 Thermal Wave Imaging (TWI) and Time-Resolved Infrared Radiometry (TRIR)
187
10.3.6 Sonic Thermal NDT
188
10.3.7 Thermoelastic Stress Analysis
188
10.4 Medical and Biological Applications
189
10.5 Military and Civil Surveillance and Other Applications
191
References
192
Appendix A: Objective Measurement of MRTD and MDTD 195
A.1 Performance Parameters That Determine MRTD and MDTD
195
A.2 Theory for MRTD Measurement
195
A.2.1 MRTD Model A (Video or Display)
196
A.2.2 MRTD Model B
197
A.3 Theory for MDTD Measurement
200
A.3.1 MDTD Model A
200
A.3.2 MDTD Model B
201
A.3.3 MDTD Model C
201
References
201
Appendix B: Sampled Imaging Systems and Aliasing 203
B.1 What Are Sampled Imaging Systems?
203
B.2 Image Formation by Sampled Imaging System
203
B.3 Basic Theory
205
B.4 Measures of Aliasing
210
B.5 MTF Measurement Techniques
211
References
212
Index 213
Bromley, Kent, England, UK