Infrared Thermal Imaging

Michael Vollmer received his PhD degree for studies of clusters on surfaces, and his habilitation on optical properties of metal clusters from the University of Heidelberg, Germany. Later assignments were with the University of Kassel, Germany, the university of California in Berkeley, USA, as well as with various institutions in the United States and Asia during sabbaticals. His research interests include atmospheric optics, spectroscopy, infrared thermal imaging, and the didactics of physics. Professor Vollmer has authored one science book and co-authored a scientific monograph and about 230 scientific and didactical papers.Klaus-Peter Möllmann received his PhD from the Humboldt University of Berlin, Germany, studying strongly doped narrow band semiconductors at low temperatures and later, for his habilitation, MCT photo detectors. He subsequently held positions with the Humboldt University and with several businesses in industry. Professor Möllmann's research interests include MEMS technology, infrared thermal imaging, and spectroscopy. He is the co-author of about 150 scientific and didactical papers.Both authors are professors of experimental physics at the University of Applied Sciences in Brandenburg, Germany.

• Preface to Second Edition XVIIPreface to First Edition XIXList of Acronyms XXIII1 Fundamentals of Infrared Thermal Imaging 11.1 Introduction 11.2 Infrared Radiation 61.2.1 ElectromagneticWaves and the Electromagnetic Spectrum 61.2.2 Basics of Geometrical Optics for Infrared Radiation 101.2.2.1 Geometric Properties of Reflection and Refraction 101.2.2.2 Specular and Diffuse Reflection 121.2.2.3 Portion of Reflected and Transmitted Radiation: Fresnel Equations 121.3 Radiometry and Thermal Radiation 141.3.1 Basic Radiometry 151.3.1.1 Radiant Power, Excitance, and Irradiance 151.3.1.2 Spectral Densities of Radiometric Quantities 151.3.1.3 Solid Angles 161.3.1.4 Radiant Intensity, Radiance, and Lambertian Emitters 171.3.1.5 Radiation Transfer between Surfaces: Fundamental Law of Radiometry and View Factor 201.3.2 Blackbody Radiation 211.3.2.1 Definition 211.3.2.2 Planck Distribution Function for Blackbody Radiation 221.3.2.3 Different Representations of Planck’s Law 241.3.2.4 Stefan–Boltzmann Law 261.3.2.5 Band Emission 261.3.2.6 Order-of-Magnitude Estimate of Detector Sensitivities of IR Cameras 291.4 Emissivity 311.4.1 Definition 311.4.2 Classification of Objects according to Emissivity 321.4.3 Emissivity and Kirchhoff’s Law 321.4.4 Parameters Affecting Emissivity Values 341.4.4.1 Material 341.4.4.2 Irregular Surface Structure 341.4.4.3 Viewing Angle 351.4.4.4 Regular Geometry Effects 391.4.4.5 Wavelength 411.4.4.6 Temperature 421.4.4.7 Conclusion 431.4.5 Techniques toMeasure/Guess Emissivities for PracticalWork 441.4.6 Blackbody Radiators: Emissivity Standards for Calibration Purposes 451.5 Optical Material Properties in IR 491.5.1 Attenuation of IR Radiation while Passing throughMatter 501.5.2 Transmission of Radiation through the Atmosphere 511.5.3 Transmission of Radiation through Slablike SolidMaterials 541.5.3.1 Nonabsorbing Slabs 541.5.3.2 Absorbing Slabs 551.5.4 Examples of Transmission Spectra of Optical Materials for IR Thermal Imaging 561.5.4.1 Gray Materials in Used IR Spectral Ranges 561.5.4.2 Some Selective Absorbers 611.6 Thin Film Coatings: IR Components with Tailored Optical Properties 621.6.1 Interference ofWaves 631.6.2 Interference and Optical Thin Films 641.6.3 Examples of AR Coatings 651.6.4 Other Optical Components 661.7 Some Notes on the History of Infrared Science and Technology 691.7.1 Infrared Science 691.7.1.1 Discovery of Heat Rays and Atmospheric Absorption 691.7.1.2 Blackbodies and Blackbody Radiation 721.7.1.3 Radiation Laws 731.7.2 Development of Infrared Technology 761.7.2.1 Prerequisites for IR Imaging 771.7.2.2 Quantitative Measurements 841.7.2.3 Applications and Imaging Techniques 88References 972 Basic Properties of IR Imaging Systems 1072.1 Introduction 1072.2 Detectors and Detector Systems 1072.2.1 Parameters That Characterize Detector Performance 1082.2.2 Noise Equivalent Temperature Difference 1102.2.3 Thermal Detectors 1112.2.3.1 Temperature Change of Detector 1112.2.3.2 Temperature-Dependent Resistance of Bolometer 1122.2.3.3 NEP and D* forMicrobolometer 1132.2.4 Photon Detectors 1172.2.4.1 Principle of Operation and Responsivity 1172.2.4.2 D* for Signal-Noise-Limited Detection 1192.2.4.3 D* for Background Noise Limited Detection 1202.2.4.4 Necessity to Cool Photon Detectors 1232.2.5 Types of Photon Detectors 1252.2.5.1 Photoconductors 1252.2.5.2 Photodiodes 1262.2.5.3 Schottky Barrier Detectors 1282.2.5.4 Quantum Well IR Photodetectors 1282.2.5.5 Recent Developments in IR Detector Technology 1322.3 Basic Measurement Process in IR Imaging 1422.3.1 Radiometric Chain 1422.3.2 Wavebands for Thermal Imaging 1462.3.3 Selecting the AppropriateWaveband for Thermal Imaging 1472.3.3.1 Total Detected Amount of Radiation 1482.3.3.2 Temperature Contrast–Radiation Changes upon Temperature Changes 1512.3.3.3 Influence of Background Reflections 1552.3.3.4 Influence of Emissivity and Emissivity Uncertainties 1582.3.3.5 Potential use of Bolometers in MWor SWband 1682.4 Complete Camera Systems 1732.4.1 Camera Design – Image Formation 1732.4.1.1 Scanning Systems 1742.4.1.2 Staring Systems–Focal-Plane Arrays 1762.4.1.3 Nonuniformity Correction 1802.4.1.4 Bad Pixel Correction 1862.4.2 Photon Detector versus Bolometer Cameras 1862.4.3 Detector Temperature Stabilization and Detector Cooling 1882.4.4 Optics and Filters 1912.4.4.1 Spectral Response 1912.4.4.2 Chromatic Aberrations 1912.4.4.3 Field of View 1922.4.4.4 Extender Rings 1952.4.4.5 Narcissus Effect 1962.4.4.6 Spectral Filters 1992.4.5 Calibration 2002.4.6 Camera Operation 2042.4.6.1 Switch-On Behavior of Cameras 2052.4.6.2 Thermal Shock Behavior 2062.4.7 Camera Software – Software Tools 2082.5 Camera Performance Characterization 2092.5.1 Temperature Accuracy 2092.5.2 Temperature Resolution – Noise Equivalent Temperature Difference (NETD) 2102.5.3 Spatial Resolution – IFOV and Slit Response Function 2132.5.4 Image Quality: MTF, MRTD, and MDTD 2162.5.5 Time Resolution – Frame Rate and Integration Time 221References 2263 AdvancedMethods in IR Imaging 2293.1 Introduction 2293.2 Spectrally Resolved Infrared Thermal Imaging 2293.2.1 Using Filters 2303.2.1.1 Glass Filters 2313.2.1.2 Plastic Filters 2333.2.1.3 Influence of Filters on Object Signal and NETD 2343.2.2 Two-Color or Ratio Thermography 2363.2.2.1 Neglecting Background Reflections 2373.2.2.2 Approximations of Planck’s Radiation Law 2403.2.2.3 Tobj Error for True Gray Bodies withinWien Approximation 2423.2.2.4 Additional Tobj Errors Owing to Nongray Objects 2463.2.2.5 Ratio Versus Single-Band-Radiation Thermometry 2473.2.2.6 Exemplary Application of Two-Color Thermography 2483.2.2.7 Extension of Ratio Method and Applications 2543.2.3 Multi- and Hyperspectral Infrared Imaging 2563.2.3.1 Principal Idea 2563.2.3.2 Basics of FTIR Spectrometry 2583.2.3.3 Advantages of FTIR Spectrometers 2623.2.3.4 Example of a Hyperspectral Imaging Instrument 2633.3 Superframing 2653.3.1 Method 2663.3.2 Example of High-Speed Imaging and Selected Integration Times 2683.3.3 Cameras with Fixed Integration Time 2703.4 Polarization in Infrared Thermal Imaging 2713.4.1 Polarization and Thermal Reflections 2723.4.1.1 Transition from Directed to Diffuse Reflections from Surfaces 2723.4.1.2 Reflectivities for SelectedMaterials in the Thermal Infrared Range 2763.4.1.3 Measuring Reflectivity Spectra: Laboratory Experiments 2783.4.1.4 Identification and Suppression of Thermal Reflections: Practical Examples 2813.4.2 Polarization-Sensitive Thermal Imaging 2843.5 Processing of IR Images 2853.5.1 Basic Methods of Image Processing 2873.5.1.1 Image Fusion 2873.5.1.2 Image Building 2893.5.1.3 Image Subtraction 2903.5.1.4 Consecutive Image Subtraction: Time Derivatives 2933.5.1.5 Consecutive Image Subtraction: High-Sensitivity Mode 2963.5.1.6 Image Derivative in Spatial Domain 2963.5.1.7 Infrared Image Contrast and Digital Detail Enhancement 3003.5.2 Advanced Methods of Image Processing 3093.5.2.1 Preprocessing 3113.5.2.2 Geometrical Transformations 3133.5.2.3 Segmentation 3143.5.2.4 Feature Extraction and Reduction 3163.5.2.5 Pattern Recognition 3193.5.2.6 Deblurring of Infrared Images 3213.6 Active Thermal Imaging 3273.6.1 Transient Heat Transfer – ThermalWave Description 3303.6.2 Pulse Thermography 3333.6.3 Lock-in Thermography 3373.6.3.1 Nondestructive Testing of Metals and Composite Structures 3403.6.3.2 Solar Cell Inspection 3433.6.4 Pulsed Phase Thermography 345References 3464 Some Basic Concepts in Heat Transfer 3514.1 Introduction 3514.2 The Basic Heat TransferModes: Conduction, Convection, and Radiation 3524.2.1 Conduction 3524.2.2 Convection 3554.2.3 Radiation 3564.2.4 Convection Including Latent Heats 3574.3 Selected Examples of Heat Transfer Problems 3594.3.1 Overview 3594.3.2 Conduction within Solids: The Biot Number 3614.3.3 Steady-State Heat Transfer through One-DimensionalWalls and U-Value 3644.3.4 Heat Transfer ThroughWindows 3694.3.5 Steady-State Heat Transfer in Two- and Three-Dimensional Problems: Thermal Bridges 3704.3.6 Dew Point Temperatures 3724.4 Transient Effects: Heating and Cooling of Objects 3734.4.1 Heat Capacity and Thermal Diffusivity 3744.4.2 Short Survey of Quantitative Treatments of Time-Dependent Problems 3754.4.3 Demonstration of Transient Heat Diffusion 3774.4.4 Typical Time Constants for Transient Thermal Phenomena 3774.4.4.1 Cooling Cube Experiment 3794.4.4.2 Theoretical Modeling of Cooling of Solid Cubes 3794.4.4.3 Time Constants for Different Objects 3824.5 Some Thoughts on the Validity of Newton’s Law 3834.5.1 Theoretical Cooling Curves 3834.5.2 Relative Contributions of Radiation and Convection 3854.5.3 Experiments: Heating and Cooling of Light Bulbs 389References 3925 Basic Applications for Teaching: Direct Visualization of Physics Phenomena 3935.1 Introduction 3935.2 Mechanics: Transformation of Mechanical Energy into Heat 3945.2.1 Sliding Friction andWeight 3945.2.2 Sliding Friction during Braking of Bicycles and Motorcycles 3955.2.3 Sliding Friction: the Finger or Hammer Pencil 3985.2.4 Inelastic Collisions: Tennis 3985.2.5 Inelastic Collisions: The Human Balance 4015.2.6 Temperature Rise of Floor and Feet whileWalking 4025.2.7 Temperature Rise of Tires during Normal Driving of a Vehicle 4035.2.8 Generating Heat by Periodic Stretching of Rubber 4045.3 Thermal Physics Phenomena 4065.3.1 Conventional Hot-Water-Filled Heaters 4075.3.2 Thermal Conductivities 4075.3.3 Conduction of Heat in Stack of Paper 4105.3.4 Convection in Liquids 4105.3.5 Convection Effects Due to Gases 4145.3.6 Evaporative Cooling 4145.3.7 Adiabatic Heating and Cooling 4175.3.8 Heating of Cheese Cubes 4185.3.9 Cooling of Bottles and Cans 4225.4 Electromagnetism 4245.4.1 Energy and Power in Simple Electric Circuits 4245.4.2 Eddy Currents 4265.4.3 Thermoelectric Effects 4275.4.4 Experiments with Microwave Ovens 4295.4.4.1 Setup 4295.4.4.2 Visualization of Horizontal Modes 4305.4.4.3 Visualization of Vertical Modes 4315.4.4.4 Aluminum Foil in Microwave Ovens 4315.5 Optics and Radiation Physics 4325.5.1 Transmission ofWindow Glass, NaCl, and SiliconWafers 4335.5.2 From Specular to Diffuse Reflection 4355.5.3 Some Light Sources 4375.5.4 Blackbody Cavities 4375.5.5 Emissivities and Leslie Cube 439Contents XI5.5.6 From Absorption to Emission of Cavity Radiation 4415.5.7 Selective Absorption and Emission of Gases 443References 4446 Shortwave Infrared Thermal Imaging 4476.1 Introduction 4476.2 The Why and How of SWInfrared Imaging 4476.3 Some Applications of SWInfrared Imaging 4506.3.1 Water OpticalMaterial Properties 4526.3.2 Cameras Used in the Experiments 4526.3.3 Selected Examples of SWImaging 4546.3.3.1 High-Temperature Measurements 4546.3.3.2 Vegetation Studies 4566.3.3.3 Sky-to-Cloud Contrast Enhancement 4586.3.3.4 Sorting Plastics and Detecting Liquid Levels in Plastic Containers 4606.3.3.5 Looking Beneath the Surface 4616.3.3.6 Undamaged Fresh Fruit/Vegetable Test 4666.3.3.7 Material Properties of Liquids 4676.3.3.8 Moisture onWalls 4706.3.3.9 Other Applications of SW Imaging 4706.4 Survey of Commercial Systems 472References 4727 IR Imaging of Buildings and Infrastructure 4777.1 Introduction 4777.1.1 Publicity of IR Images of Buildings 4787.1.2 Just Colorful Images? 4797.1.2.1 Level and Span 4807.1.2.2 Choice of Color Palette 4807.1.2.3 More on Palette, Level, and Span 4807.1.3 General Problems Associated with Interpretation of IR Images 4857.1.4 Energy Standard Regulations for Buildings 4887.2 Some Standard Examples for Building Thermography 4907.2.1 Half-Timbered Houses behind Plaster 4907.2.2 Other Examples with OutsideWalls 4937.2.3 Determining whether a Defect Is Energetically Relevant 4947.2.4 The Role of Inside Thermal Insulation 4977.2.5 Floor Heating Systems 4987.3 Geometrical Thermal Bridges versus Structural Problems 5007.3.1 Geometrical Thermal Bridges 5007.3.2 Structural Defects 5047.4 External Influences 5077.4.1 Wind 5077.4.2 Effect of Moisture in Thermal Images 5097.4.3 Solar Load and Shadows 5137.4.3.1 Modeling Transient Effects Due to Solar Load 5137.4.3.2 Experimental Time Constants 5167.4.3.3 Shadows 5187.4.3.4 Solar Load of Structures withinWalls 5197.4.3.5 Direct Solar Reflections 5207.4.4 General View Factor Effects in Building Thermography 5257.4.5 Night Sky Radiant Cooling and the View Factor 5287.4.5.1 Cars Parked Outside or Below a Carport 5297.4.5.2 Walls of Houses Facing a Clear Sky 5317.4.5.3 View Factor Effects: Partial Shielding ofWalls by Carport 5317.4.5.4 View Factor Effects: The Influence of Neighboring Buildings and Roof Overhang 5337.5 Windows 5347.5.1 General Features 5347.5.2 Optically Induced Thermal Effects 5397.6 Thermography and Blower-Door Tests 5417.6.1 Close-Up Studies 5437.6.2 Overview Studies 5477.7 Quantitative IR Imaging: Total Heat Transfer through Building Envelope 5497.8 New Developments and Conclusions 552References 5568 Industrial Application: Detection of Gases 5618.1 Introduction 5618.2 Spectra of Molecular Gases 5618.3 Influences of Gases on IR Imaging: Absorption, Scattering, and Emission of Radiation 5678.3.1 Introduction 5678.3.2 Interaction of Gases with IR Radiation 5678.3.3 Influence of Gases on IR Signals from Objects 5698.4 Absorption by Cold Gases: Quantitative Aspects 5728.4.1 Attenuation of Radiation by a Cold Gas 5728.4.2 From Transmission Spectra to Absorption Constants 5748.4.3 Transmission Spectra for Arbitrary Gas Conditions and IR Camera Signal Changes 5748.4.4 Calibration Curves for Gas Detection 5778.4.5 Problem: the Enormous Variety ofMeasurement Conditions 5788.5 Thermal Emission from Hot Gases 5808.6 New Developments 5828.7 Practical Examples: Gas Detection with Commercial IR Cameras 5888.7.1 Organic Compounds 5888.7.2 Some Inorganic Compounds 5918.7.3 CO2: Gas of the Century 5948.7.3.1 Comparison of Broadband and Narrowband Detection 5968.7.3.2 Detecting Volume Concentration of CO2 in Exhaled Air 5978.7.3.3 Absorption, Scattering, and Thermal Emission of IR Radiation 5978.7.3.4 Quantitative Result: Detecting Minute Amounts of CO2 in Air 5998.7.3.5 Quantitative Result: Detection ofWell-Defined CO2 Gas Flows from a Tube 5998.A Appendix: Survey of Transmission Spectra of Various Gases 6028.A.1 Inorganic Compounds 1 6048.A.2 Inorganic Compounds 2 6058.A.3 Simple Hydrocarbons 1 6068.A.4 Simple Hydrocarbons 2 6078.A.5 Simple Multiple Bond Compounds and Some Alcohols 6088.A.6 Some Ketones/Ethers 6098.A.7 Some Benzene Compounds 6108.A.8 Some HydrocarbonsWith Halogens 611References 6129 Microsystems 6159.1 Introduction 6159.2 Special Requirements for Thermal Imaging 6169.2.1 Mechanical Stability of Setup 6169.2.2 Microscope Objectives, Close-up Lenses, Extender Rings 6169.2.3 High-Speed Recording 6189.2.4 Temperature Measurement 6189.3 Microfluidic Systems 6199.3.1 Microreactors 6199.3.1.1 Stainless Steel Falling Film Microreactor 6199.3.1.2 Glass Microreactor 6239.3.1.3 Silicon Microreactor 6259.3.2 Micro Heat Exchangers 6269.4 Microsensors 6289.4.1 Thermal IR Sensors 6289.4.1.1 IR Thermopile Sensors 6299.4.1.2 IR Bolometer Sensors 6329.4.2 Semiconductor Gas Sensors 6359.5 Microsystems with Electric to Thermal Energy Conversion 6379.5.1 Miniaturized IR Emitters 6379.5.2 Micro Peltier Elements 6399.5.3 Cryogenic Actuators 640References 64210 Selected Topics in Industry 64510.1 Introduction 64510.2 Miscellaneous Industrial Applications 64510.2.1 Predictive Maintenance and Quality Control 64510.2.2 Pipes and Valves in a Power Plant 64710.2.3 Levels of Liquids in Tanks in Petrochemical Industry 64810.2.4 Polymer Molding 65110.2.5 Rack-Storage Fire Testing 65210.3 Low-Voltage Electrical Applications 65310.3.1 Early Microelectronic Boards 65410.3.2 Macroscopic Electric Boards 65510.3.3 ModernMicroelectronic Boards 65610.4 High-Voltage Electrical Applications 65610.4.1 Substation Transformers 65710.4.2 Overheated High-Voltage Line 65910.4.3 Electric Fan Defects 66010.4.4 Oil Levels in High-Voltage Bushings 66010.5 Metal Industry and High Temperatures 66210.5.1 Direct Imaging of HotMetal Molds 66210.5.2 Manufacturing Hot SolidMetal Strips: Thermal Reflections 66310.5.3 Determination of Metal Temperatures if Emissivity Is Known 66510.5.4 Determining Metal Temperatures for Unknown Emissivity: Gold Cup Method 66610.5.5 Determining Metal Temperatures for Unknown Emissivity:Wedge and Black Emitter Method 66710.5.6 Other Applications of IR Imaging in Metal Industry or at High Temperatures 66910.6 Automobile Industry 67010.6.1 Quality Control of Heating Systems 67110.6.2 Active and Passive IR Night Vision Systems 67210.6.3 IR Imaging of Race Cars 67510.6.4 Motorcycles 67610.7 Airplane and Spacecraft Industry 67610.7.1 Imaging of Aircraft 67610.7.2 Imaging of Spacecraft 67810.8 Plastic Foils 68310.8.1 Spectra: Selective Emitters 68310.8.2 Images: Looking through Plastics 68510.9 Surveillance and Security: Range of IR Cameras 68710.9.1 Applications in Surveillance 68710.9.2 Range of IR Cameras 68810.10 Line Scanning Thermometry ofMoving Objects 69410.11 Remote Sensing Using IR Imaging 69510.11.1 Survey ofMethods 69510.11.2 Some IR Imaging Applications Using Drones 699References 70211 Selected Applications in Other Fields 70911.1 Medical Applications 70911.1.1 Introduction 70911.1.2 Diagnosis andMonitoring of Pain 71211.1.3 Acupuncture 71611.1.4 Breast Thermography and Detection of Breast Cancer 71811.1.5 Other Medical Applications 71911.1.5.1 Raynaud’s Phenomenon 71911.1.5.2 Pressure Ulcers 72011.2 Animals and Veterinary Applications 72111.2.1 Pets 72211.2.2 Zoo Animals 72311.2.3 Equine Thermography 72511.2.4 Wildlife 72611.3 Sports 72911.3.1 High-Speed Recording of Tennis Serve 72911.3.2 Squash and Volleyball 73211.3.3 Other Applications in Sports 73411.4 Arts: Music, Contemporary Dancing, and Paintings 73511.4.1 Musical Instruments 73511.4.2 Contemporary Dance 73711.4.3 Paintings 74011.5 Nature 74211.5.1 Sky and Clouds 74211.5.2 Wildfires 74611.5.3 Sun and Moon 74911.5.4 InfraredMirages 75211.5.5 Geothermal Phenomena 75411.5.5.1 Geysers and Hot Springs 75411.5.5.2 IR Thermal Imaging in Volcanology 756References 760Index 765

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