CONTENTS
1.WHY MICROWAVES? 1
1.1 Overview of Microwave Systems 2
1.1.2 Information from Passive Microwave Imagers Information from Passive Microwave Sounders 2.
1.1.3 Information from Active Microwave Instruments 3
1.1.4 How Can This Information be Used? 5
2. A BRIEF HISTORY OF MICROWAVES 7
2.1 In the Beginning 8
2.2 Out of the Darkness: Maxwell and Hertz 8
2.3 Radios, Death Rays and Radar 14
2.4 The Venus Ruler and Little Green Men 18
2.5 Imaging Radar 20
2.6 Microwave Remote Sensing from Space 21
2.7 Further Reading 22
3. PHYSICAL FUNDAMENTALS 23
3.1Physical Properties of EM Waves 23
3.1.1 Electromagnetic Radiation as Waves 24
3.1.2 Complex Wave Description 28
3.2 Energy and Power of Waves 29
3.2.1 Polarisation 31
3.3 Combination of Waves 33
3.3.1 Coherence 34
3.4 The Most Important Section in This Book 37
3.4.1 Phase as a (Relative) Distance Measure 37
3.4.2 Combining Two Waves in 2-D 39
3.4.3 Quantifying the Interference Pattern 43
3.4.4 Passive Case 45
3.4.5 Multiple Source Interference Pattern 47
3.4.6 Beamwidth and Angular Resolution 48
3.4.7 Huygens' Wavelets 50
3.4.8 More on Coherence 51
3.5 Propagation of Microwaves 53
3.5.1 Through Lossy Media 55
3.5.2 Moving Sources 56
3.6 Where Do Microwaves Come From? 57
3.6.1 How Are They Produced in Nature? 57
3.6.2 Radiation Laws 60
3.6.3 How Are Microwaves Produced Artificially? 62
3.7 Further reading 64
POLARIMETRY 65
4.1 Describing polarised waves 66
4.1.1 Summary of linear basis 67
4.2 Superposition of polarized waves 68
4.3 Representing polarization 73
4.3.1 Poincare sphere 73
4.3.2 Mathematical Description 74
4.3.3 Stokes Vector 74
4.3.4 Brightness Stokes Vector 76
4.3.5 Partially Polarised Waves 76
4.3.6 The Stokes Scattering Matrix 78
4.3.7 The Scattering Matrix 80
4.3.8 Target Vector 80
4.3.9 Covariance Matrix 81
4.4 Passive Polarimetry 82
4.5 Polarimetry in Radar 82
4.5.1 Radar Polarimeters 82
4.5.2 Polarimetric Synthesis and Response Curves 83
4.6 Important Polarimetric Properties 85
4.6.1 Unpolarised Power 87
4.6.2 Degree of Polarisation and Coefficient of Variation 87
4.6.3 Polarimetric Ratios 88
4.6.4 Coherent Parameters 89
4.6.5 Polarimetric Decomposition 90
4.7 Further Reading 91
5. MICROWAVES IN THE REAL WORLD 93
5.1 Continuous Media and the Atmosphere
5.1.1Radiative Transfer Theory 94
5.1.2 Microwave Brightness Temperature 96
5.1.3 Spectral Lines 98
5.1.4 Line Broadening 100
5.1.5 Faraday Rotation 101
5.2 Interaction With Discrete Objects 102
5.2.1 Diffraction 103
5.2.2 Importance of Diffraction 104
5.2.3 Scattering 105
5.2.4 Radar Cross-section 106
5.2.5 Importance of Scattering Theory 110
5.3 Scattering and Emission from Volumes 112
5.3.1 Transmission Through Volumes 113
5.3.2 Emission 114
5.3.3 Scattering 116
5.4 Reflection and Emission from Smooth Surfaces 118
5.4.1 Scattering from Smooth Boundaries 120
5.4.2 Emission from Smooth Boundaries 123
5.4.3 Summary 124
5.5 Scattering and Emission from Rough Surfaces 124
5.5.1 Definition of "Rough" 124
5.5.2 Effects of Roughness 125
5.5.3 Summary 126
5.6 Non-Random (Periodic) Surfaces 127
5.7 Scattering and Emission from Natural Surfaces 126
5.7.1 Oceans and Lakes 129
5.7.2 Hydrometeors 132
5.7.3 Ice and Snow 133
5.7.4 Freshwater Ice 134
5.7.5 Glacial Ice 135
5.7.6 Sea Ice 136
5.7.7 Bare Rock and Deserts 138
5.7.8 Soils 139
5.7.9 Vegetation 142
5.8 Special Scatterers 144
5.8.1 Corner Reflectors 144
5.8.2 Moving Targets 146
5.8.3 Mixed Targets 147
5.9 Further Reading 149
6. DETECTING MICROWAVES 151
6.1General Approach 151
6.2 Conceptual Approach to Microwave Systems 153
6.2.1 A Word of Warning 154
6.3 Basic Microwave Radiometer 154
6.4The Antenna 154
6.4.1 Parabolic Antennas 155
6.4.2 The Dipole Antenna 157
6.4.3 Array Antennas 159
6.4.4 Antenna Properties 160
6.5 The Receiver 163
6.5.1 Detector 165
6.6 Coherent Systems 165
6.7 Active Systems 166
6.8 System Performance 167
6.8.1 Noise and Sensitivity 167
6.8.2 Sensitivity Considerations for Receivers 167
6.8.3 Other Sources of Uncertainty 169
6.9 Calibration 169
6.9.1 Antenna Calibration 172
6.9.2 Verification and Validation 173
6.9.3 Types of Calibration 173
6.9.4 Strategies for Calibrating Receivers 175
6.10 Final Remarks on Calibration 176
6.11 Further Reading 177
7. ATMOSPHERIC SOUNDING 179
7.1 Atmospheric Sounding 180
7.1.1 The Need for Measurements 180
7.1.2 The Earth's Atmosphere 181
7.1.3 Water Vapour and Oxygen 182
7.1.4 Clouds and Precipitation 183
7.1.5 Ozone 183
7.1.6 Chlorine Monoxide 184
7.1.7 Other Relevant Measurements 184
7.2 Principles of Measurement 184
7.3 Theoretical Basis of Sounding 186
7.3.1 The Forward Model 186
7.3.2 Simple Formulation of the Forward Model 188
7.3.3 The Inverse Model 189
7.3.4 Solving the Inverse Problem 191
7.3.5 The Influence Functions 194
7.4 Viewing Geometries 195
7.4.1 Nadir Sounding 195
7.4.2 Limb Sounding 197
7.5 Passive Rainfall Mapping 200
7.5.1 The Need for Measurements 200
7.5.2 Principles of Measurement 200
7.5.3 Emission Method 201
7.5.4 Scattering Method 201
7.6 Further Reading 202
8. PASSIVE IMAGING 205
8.1 Principles of Measurement 206
8.1.1 Background 206
8.1.2 Practical Radiometers 206
8.1.3 Viewing Geometries 207
8.1.4 The Generic Forward Model 207
8.2 Oceans 209
8.2.1 The Need for Measurements 211
8.2.2 Principles of Measurement: SST 211
8.2.3 Principles of Measurement: Ocean Salinity 212
8.2.4 Principles of Measurement: Ocean Winds 213
8.3 Sea Ice
8.3.1 The Need for Measurements 213
8.3.2 Sea Ice Concentration 214
8.4 Land 217
8.4.1 The Need for Measurements 217
8.4.2 The Forward Problem Over Land 218
8.4.3 Empirical Approaches to Snow Depth 219
8.4.4 A Final Comment on Passive Polarimetry 220
8.5 Further Reading 220
9. ACTIVE MICROWAVES 221
9.1 Principles of Measurement 222
9.1.1 What is RADAR? 223
9.1.2 Basic Radar Operation 224
9.2 The Generic Equations of Radar Performance 225
9.2.1The Radar Equation 225
9.2.2 Range resolution 227
9.3 Radar Altimeters 231
9.3.1 The Need for Altimeter Measurements 232
9.3.2 Altimeter Geometry 235
9.3.3 Instrumentation 236
9.3.4 Echo Shape Analysis 237
9.3.5 Range Ambiguity 241
9.3.6 Accuracy of Height Retrievals 243
9.3.7 Scanning Altimeters 245
9.3.8 Calibration and Validation 246
9.4 Improving Directionality 247
9.4.1 Sub-Beamwidth Resolution 248
9.4.2 Synthetic Aperture Altimeters 249
9.5 Scatterometers
9.5.1 The Need for Scatterometer Measurements 251
9.5.2 General Operation 252
9.5.3 Rain Radar 253
9.5.4 Windscatterometers 254
9.5.5 Polarimetric Scatterometers 257
9.6 Further Reading 257
10. IMAGING RADAR 259
10.1 The Need for Imaging Radar 259
10.1.1 Oceans 260
10.2.2 Sea Ice 261
10.1.3 Terrestrial Surfaces 262
10.1.4 The Water Cloud Model for Vegetation 263
10.1.5 Other Uses of Radar Imagery 264
10.2 What is an Image? 265
10.3 Radar Image Construction 267
10.4 Side-Looking Airborne Radar 268
10.4.1 Ground Range resolution 269
10.4.2 Azimuth Resolution 270
10.5 Synthetic Aperture Radar (SAR) 271
10.5.1 Aperture Synthesis: A Doppler Interpretation 271
10.5.2 Aperture Synthesis: A Geometric Explanation 275
10.5.3 Geometry vs. Doppler 278
10.5.4 SAR Focussing 280
10.6 Radar Equation for SAR 271
10.7 Geometric Distortions in Radar Images 281
10.7.1 Lay-over and Foreshortening 281
10.7.2 Radar Shadow 282
10.7.3 Motion Errors 283
10.7.4 Moving Targets 284
10.8 Operational Limits 284
10.8.1 Ambiguities 285
10.8.2 Coverage vs PRF 286
10.9 Other SAR Modes 287
10.9.1 ScanSAR Operation 287
10.9.2 Spotlight Mode 287
10.10 Working With SAR Images 287
10.10.1 Speckle 289
Speckle Statistics 292
Speckle Filtering 296
10.10.4 Geometric Correction 297
10.10.5 Limitations of Geometric Correction 299
10.11 SAR Data Formats 300
10.12 Extracting Topography from SAR Images 301
10.12.1 Stereo SAR Radargrammetry 302
10.12.2 SAR Clinometry 302
10.13 Further Reading 303
11. INTERFEROMETRY 305
11.1 The Need for Interferometric Measurements 305
11.2 Principles of Interferometry 306
11.2.1 Phase Measurements 306
11.2.2 Application of Dual Systems 307
11.2.3 Interferometry for Resolving Direction 309
11.3 Passive Imaging Interferometry 310
11.4 Radar Interferometry 312
11.4.1 Interferometric Altimetry 312
11.4.2 Interferometric SAR 313
11.4.3 InSAR Viewing Geometries 315
11.4.4 Interferometric Coherence Magnitude 325
11.4.5 Decorrelation 327
11.4.6 Summary of Decorrelation 329
11.5 Practical DEM Generation 331
11.5.1 InSAR Processing Chain 332
11.6 Vegetation Height Estimation 333
11.6.1 Single Frequency 334
11.6.2 Dual-Frequency 334
11.6.3 Polarimetric Interferometry and Multibaseline Interferometry 335
11.6.4 SAR Tomography 335
11.7 Differential SAR Interferometry 336
11.7.1 Considerations and Limitations 338
11.7.2 Atmospheric Water Vapour 339
11.8 Permanent Scatterer Interferometry 340
11.9 Along-Track Interferometry 341
11.10 Further Reading 342
APPENDIX: Summary of Useful Mathematics 343
A.1 Angles 343
A.1.1 Degrees 343
A.1.2 Radians 343
A.1.3 Steradian (solid angle) 344
A.2 Some Useful Trigonometric Relations 344
A.3 Logs and Exponentials 344
A.3.4 Some Fundamental Properties 345
A.3.5 Special values 345
A.3.6 Series Expansions 346
A.4 Complex Numbers 346
A.5 Vectors 349
A.5.7 Law of Vector Algebra 349
A.5.8 Cross or Vector Product 349
A.6 Matrices 350
A.6.9 Matrix Algebra
bibiliography 353
index 357