Table Of ContentInfrared Thermography
Microwave Technology Series
The Microwave Technology Series publishes authoritative works for professional
engineers, researchers and advanced students across the entire range of microwave
devices, sub-systems, systems and applications. The series aims to meet the reader's
needs for relevant information useful in practical applications. Engineers involved
in microwave devices and circuits, antennas, broadcasting communications, radar,
infra-red and avionics will find the series an invaluable source of design and
reference information.
Series editors:
Michel-Henri Carpentier
Professor in 'Grandes Ecoles', France,
Fellow of the IEEE, and President of the French SEE
Bradford L. Smith
International Patents Consultant and Engineer
with the Alcatel group in Paris, France,
and a Senior Member of the IEEE and French SEE
Titles available
1. The Microwave Engineering Handbook Volume 1
Microwave components
Edited by Bradford L. Smith and Michel-Henri Carpentier
2. The Microwave Engineering Handbook Volume 2
Microwave circuits, antennas and propagation
Edited by Bradford L. Smith and Michel-Henri Carpentier
3. The Microwave Engineering Handbook Volume 3
Microwave systems and applications
Edited by Bradford L. Smith and Michel-Henri Carpentier
4. Solid-state Microwave Generation
J. Anastassiades, D. Kaminsky, E. Perea and A. Poezevara
5. Infrared Thermography
G. Gaussorgues
6. Phase Locked Loops
J.B. Encinas
7. Frequency Measurement and Control
Chronos Group
8. Microwave Integrated Circuits
Edited by I. Kneppo
Infrared Thermography
G. Gaussorgues
Technical Director, HGH lnfrared System
Massy, and
Director, Electro-oprics Laboratory of the French Navy,
Fruna
Translated by
s.
Chomet
Department of Physics
King's College
Vniversity of London
VK
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SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
English language edition 1994
© 1994 Springer Science+Business Media Dordrecht
Originally published by Chapman & Hali in 1994
Softcover reprint ofthe hardcover lst edition 1994
Original French language edition - La Therrrwgraphie lnfrarouge
Principes, Technologies, Applications (3rd edition, revised) - © 1989
Technique et Documentation - Lavoisier
ISBN 978-94-010-4306-9 ISBN 978-94-011-0711-2 (eBook)
DOI 10.1007/978-94-011-0711-2
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The publisher makes no representation, express or implied, with regard
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A catalogue record for this book is available from the British Library
Contents
Colour and black and white plates showing thermograms and images recorded in
false colours appear at the end of the book
Foreword xiii
Historical Background xv
1 Revision of Radiometry 1
1.1 The radiometric chain 1
1.2 Radiant flux 2
1.3 Geometrical spreading of a beam 2
1.4 Radiance 3
1.5 Irradiance 4
1.6 Radiant exitance 5
1. 7 Radiant intensity of a source in a given direction 5
1.8 Quantity of radiation and exposure 5
1.9 Bouguer's law 6
1.10 Radiation scattering 6
1.11 Note on units 7
2 Origins of Infrared Radiation 8
3 Thermal Emission by Matter 11
3.1 Black-body radiation 11
3.1.1 Planck's law 12
3.1.2 Wien's law 13
3.1.3 Stefan-Boltzmann law 15
3.1.4 Exitance of black-body in a given spectral band 16
3.1.5 Evaluation of exitance of a body by the method of
reduced coordinates 17
3.1.6 Thermal derivation of Planck's law 22
3.1.7 Thermal contrast 23
3.2 Different types of radiator 24
3.3 Problems with the emissivity of a material 25
3.4 Thermodynamic equilibrium 26
vi Infrared Thermography
3.5 Problems with the reflectance of a material 26
3.6 Example of an application 30
3.6.1 Calculation of Te and Ee 32
3.6.2 Calculation of EO and To 34
3.7 Emissivity of materials 36
3.7.1 Spectral emissivity 36
3.7.2 Emissivity of dielectrics - the effect of temperature 37
3.7.3 Emissivity of metals - the effect of temperature 39
3.7.4 The effect of the angle of incidence on emissivity 40
3.7.5 Measurement of emissivity 42
3.7.6 The effect of emissivity in thermography 43
3.7.7 Emissivity of a rough surface 43
3.7.8 The emissivity of dihedrons and trihedrons 45
3.8 Emission from the interior of a medium 46
3.9 Other sources of infrared radiation 50
3.9.1 The Nernst filament (Nernst glower) 50
3.9.2 The globar 51
3.9.3 Electroluminescent junctions 51
3.9.4 Sources employing stimulated emission (lasers) 52
4 Transmission by the Atmosphere 61
4.1 Self-absorption by gases 62
4.2 Scattering by particles 67
4.3 Atmospheric turbulence 68
4.3.1 Diffraction by inhomogeneities 70
4.3.2 The structure function 71
4.3.3 Measurements of turbulence 74
4.4 Methods for calculating atmospheric transmission 75
4.4.1 The 'line-by-line' method 76
4.4.2 The band model method 76
4.4.3 Empirical methods employing band models 77
4.4.4 The multiparametric model 78
4.5 A practical method for calculating atmospheric transmission 78
4.5.1 Molecular absorption 78
4.5.2 Scattering by particles 81
4.5.3 Example of application 94
5 Optical Materials for the Infrared 103
5.1 Propagation of an electromagnetic wave in matter 103
5.2 Optical properties of a medium 109
5.2.1 Refraction 110
5.2.2 Dispersion 110
5.2.3 Absorption, transmission and reflection 111
5.3 Physical properties of optical materials 114
5.3.1 Hardness 115
Contents vii
5.3.2 Thermal properties 115
5.3.3 Cost of materials 116
5.4 Types of material 117
5.4.1 Glasses 117
5.4.2 Crystals 118
5.4.3 Plastics 118
5.4.4 Metals 118
5.5 Properties of some optical materials 119
5.5.1 Glasses 119
5.5.2 Crystals 125
6 Optical Image Formation 135
6.1 Geometrical optics 135
6.2 Aberrations of optical systems 136
6.2.1 Chromatic aberrations 136
6.2.2 Geometrical aberrations 139
6.3. Calculation of geometrical aberrations 159
6.3.1 Path of a marginal ray - imaging by an objective 160
6.3.2 The path of a principal - stop imaging 162
6.3.3 Paraxial rays - the Gaussian approximation 164
6.3.4 The third-order approximation 167
6.3.5 Spherical aberration 167
6.3.6 The case of aplanatic optics - the Abbe's sine condition 168
6.3.7 Calculation of coma 169
6.3.8 Astigmatism and field curvature 171
6.3.9 Distortion 172
6.4 Diffraction 173
6.4.1 Diffraction by an aperture 173
6.4.2 Image formation - linear filter theory 178
6.4.3 The optical transfer function 181
6.4.4 Optics for the infrared 188
6.4.5 Reflecting telescopes 188
6.4.6 Catadioptric telescopes 196
6.4.7 Evaluation of image-spot abberration for different simple
optical systems 196
6.4.8 Refractive optics 200
6.4.9 Simple germanium lens for A. = 10,um 201
7 Scanning and Imaging 213
7.1 Radiometers 213
7.2 Radiometers for spatial analysis 214
7.3 Thermography 220
7.4 Scanning methods 220
7.4.1 Line scanners 221
7.4.2 Image scanning 231
YIll Infrared Thermography
7.5 Imaging 232
7.6 Imaging with multi-element detectors 234
7.6.1 Two-dimensional scanning with a single detector 234
7.6.2 Scanning by a parallel array of n elements 235
7.6.3 Scanning using an array of p elements in series 239
7.6.4 Serial-parallel scanning with a two-dimensional array 240
7.7 Electronic imaging 240
7.7.1 The pyroelectric image tube 242
7.7.2 Pyroelectric arrays 243
7.7.3 Solid state arrays 243
8 Spectral Filtering 244
8.1 Spectral transmittance of materials 244
8.2 The properties of thin layers 246
8.3 Antirefiective thin films 249
8.3.1 Antirefiective coating using a single layer 249
8.3.2 Two-layer antirefiective coating 251
8.3.3 Multilayer antirefiective coating 251
8.3.4 Examples of surface treatments for improving the
transmission of materials 252
8.4 Filters 254
8.4.1 Different types of filter 255
8.4.2 Filter fabrication technologies 256
9 Radiation Detectors 261
9.1 Generalities 261
9.2 Characteristics of detectors 262
9.2.1 Current-voltage characteristic 262
9.2.2 Shape of signal 264
9.3 Noise 264
9.3.1 The spectral distribution and technological causes of noise 264
9.3.2 Signal-to-noise ratio 265
9.3.3 The noise equivalent power (NEP) 267
9.3.4 Detectivity 267
9.3.5 Detectivity limit of a perfect detector 268
9.4 Detector sensitivity 268
9.4.1 Local variation of sensitivity 268
9.4.2 Spectral sensitivity 268
9.4.3 Global sensitivity 269
9.4.4 Sensitivity as a function of frequency 270
9.5 Thermal detectors 271
9.5.1 Fluctuations 271
9.5.2 General principle of operation 271
9.5.3 Signal-to-noise ratio 273
Contents ix
9.5.4 Detectivity of heat detectors 273
9.6 Different types of thermal detector 274
9.6.1 Bolometers 274
9.6.2 Pyroelectric detectors 275
9.6.3 Thermopiles 276
9.6.5 Pneumatic detectors 276
9.7 Quantum detectors 276
9.7.1 Fluctuations 277
9.7.2 Detectivity of quantum detectors 278
9.8 Different types of quantum detector 280
9.8.1 Photoemissive detectors 280
9.8.2. Summary of solid state physics 282
9.8.3. Photoconductive detectors 284
9.8.4 Photovoltaic detectors 287
9.9 Applications of detectors 289
9.9.1 Spectral sensitivity range 289
9.9.2 Sensitivity 291
9.9.3 Noise and detectivity 292
9.9.4 Frequency response of detectors 293
9.9.5 Detector bias arrangements 294
9.9.6 Effect of detector field angle 295
9.9.7 Passivation of detectors 295
9.10 Multielement detectors 296
9.11 Detectors used in thermography 297
9.12 Charge coupled devices 298
9.12.1 Three-phase CCD 298
9.12.2 Two-phase CCD 299
9.12.3 Transfer efficiency 300
9.12.4 Reading of a detector array with a CCD 301
9.12.5 Imaging with a CCD matrix 301
9.12.6 Charge injection devices (Cms) 302
9.12.7 Spectral response and characteristics of CCD and
cm imaging devices 304
9.13 Infrared charge coupled devices (IRCCD) 304
9.13.1 HgTeCd detectors 305
9.13.2 Indium antimonide 306
9.13.3 Silicon-platinum Schottky diode 306
9.13.4 Performance of IRCCDs 307
9.14 Sprite detectors 308
9.15 Detector cooling 311
9.15.1 Cooling by liquified gas 311
9.15.2 Cooling by Joule-Thomson expansion 311
9.15.3 Cooling by cryogenic cycles 313
9.15.4 Thermoelectric cooling 316
x Infrared Thermography
10 Signal Processing 319
10.1 The analogue signal 319
10.2 Processing of analogue signals 323
10.3 Processing of digital signals 323
10.4 Example of application 324
10.4.1 Analogue acquisition 325
10.4.2 Digitisation of the signal 325
10.4.3 Visualisation 329
10.4.4 Architecture of image reconstruction 331
10.4.5 Image processing 333
10.4.6 Temperature calibration of images 334
10.4.7 Description of program 337
11 Characterisation of infrared systems 340
11.1 Generalities 340
11.1.1 Noise equivalent irradiance (NEI) 341
11.1.2 Thermal resolution 341
11.1.3 Spatial resolution 342
11.1.4 Spectral response 342
11.1.5 The signal-temperature relation 342
11.1.6 Temporal stability and drift 343
11.2 Characteristics of infrared detectors 343
11.2.1 Sensitivity 343
11.2.2 Time constant 344
11.2.3 Noise equivalent power (NEP) 344
11.2.4 Noise equivalent irradiance (NEI) 345
11.2.5 Detectivity 345
11.3 Calculation of the characteristics of infrared systems 347
11.3.1 Calculation of noise equivalent irradiance (NEI) 347
11.3.2 Calculation of noise equivalent temperature difference
(NETD) 351
11.4 Measurement of the characteristics of an infrared system 353
11.4.1 Measurement of NEI 354
11.4.2 Measurement of NETD 357
11.4.3 Measurement of MRTD 357
11.4.4 Measurement ofMDTD 359
11.4.5 Measurement of relative spectral response 359
11.4.6 Measurement of spatial resolution - the modulation
transfer function 360
11.4.7 Determination of the signal-temperature relation 363
11.4.8 Measurement of drift 368
11.5 Example: Characterisation of a system 369
11.5.1 Evaluation of NEI 370
11.5.2 Evaluation of NETD 372
11.5.3 Measurement of NEI 374
11.5.4 Measurement ofNETD 373
