Introduction to Microwave Remote Sensing

Transcription

1 Introduction to Microwave Remote Sensing lain H. Woodhouse The University of Edinburgh Scotland Taylor & Francis Taylor & Francis Group Boca Raton London New York A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Croup, the academic division of T&F Informa pic.

2 CONTENTS 1 WHY MICROWAVES? Overview of Microwave Systems Information from Passive Microwave Imagers Information from Passive Microwave Sounders Information from Active Microwave Instruments How Can This Information be Used? 5 2 A BRIEF HISTORY OF MICROWAVES In the beginning Out of the Darkness: Maxwell and Hertz Radios, Death Rays and Radar The Venus Ruler and Little Green Men Imaging Radar Microwave Remote Sensing from Space Further Reading 22 3 PHYSICAL FUNDAMENTALS Physical Properties of EM Waves Electromagnetic Radiation as Waves Complex Wave Description Energy and Power of Waves Polarisation 31 XV

3 xvi Introduction to Microwave Remote Sensing 3.3 Combination of Waves Coherence The Most Important Section in This Book Phase as a (Relative) Distance Measure Combining Two Waves in 2-D Quantifying the Interference Pattern Passive Case Multiple Source Interference Pattern Beamwidth and Angular Resolution ' Huygens' Wavelets More on Coherence Propagation of Microwaves Through Lossy Media Moving Sources Where Do Microwaves Come From? How Are They Produced in Nature? Radiation Laws How Are Microwaves Produced Artificially? Further Reading 64 4 POLARIMETRY Describing Polarised Waves Summary of Linear Basis 4.2 Superposition of Polarised Waves 4.3 Representing Polarisation Poincare sphere Mathematical Description Stokes Vector Brightness Stokes Vector Partially Polarised Waves The Stokes Scattering Matrix The Scattering Matrix Target Vector Covariance Matrix

4 Contents xvii 4.4 Passive Polarimetry Polarimetry in Radar Radar Polarimeters Polarimetric Synthesis and Response Curves 4.6 Important Polarimetric Properties Unpolarised Power Degree of Polarisation and Coefficient of Variation Polarimetric Ratios Coherent Parameters Polarimetric Decomposition Further Reading 91 5 MICROWAVES IN THE REAL WORLD Continuous Media and the Atmosphere Radiative Transfer Theory Microwave Brightness Temperature Spectral Lines Line Broadening Faraday Rotation Interaction With Discrete Objects Diffraction Importance of Diffraction Scattering Radar Cross-section Importance of Scattering Theory Scattering and Emission from Volumes Transmission Through Volumes Emission Scattering Reflection and Emission from Smooth Surfaces Scattering from Smooth Boundaries Emission from Smooth Boundaries

5 xviii Introduction to Microwave Remote Sensing Summary Scattering and Emission from Rough Surfaces Definition of "Rough" Effects of Roughness Summary Non-Random (Periodic) Surfaces Scattering and Emission from Natural Surfaces Oceans and Lakes Hydrometeors Ice and Snow Freshwater Ice Glacial Ice Sea Ice Bare Rock and Deserts Soils Vegetation 5.8 Special Scatterers Corner Reflectors Moving Targets Mixed Targets Further Reading DETECTING MICROWAVES General Approach Conceptual Approach to Microwave Systems A Word of Warning Basic Microwave Radiometer The Antenna Parabolic Antennas The Dipole Antenna Array Antennas 159

6 Contents xix Antenna Properties The Receiver Detector Coherent Systems Active Systems System Performance Noise and Sensitivity Sensitivity Considerations for Receivers Other Sources of Uncertainty Calibration Antenna Calibration Verification and Validation Types of Calibration Strategies for Calibrating Receivers Final Remarks on Calibration Further Reading ATMOSPHERIC SOUNDING Atmospheric Sounding The Need for Measurements The Earth's Atmosphere Water Vapour and Oxygen Clouds and Precipitation Ozone Chlorine Monoxide Other Relevant Measurements 7.2 Principles of Measurement 7.3 Theoretical Basis of Sounding The Forward Model Simple Formulation of the Forward Model The Inverse Model Solvina the Inverse Problem

7 xx Introduction to Microwave Remote Sensing The Influence Functions 7.4 Viewing Geometries Nadir Sounding Limb Sounding 7.5 Passive Rainfall Mapping The Need for Measurements Principles of Measurement Emission Method Scattering Method Further Reading 8 PASSIVE IMAGING 8.1 Principles of Measurement Background Practical Radiometers Viewing Geometries The Generic Forward Model 8.2 Oceans The Need for Measurements Principles of Measurement: SST Principles of Measurement: Ocean Salinity Principles of Measurement: Ocean Winds 8.3 Sea Ice The Need for Measurements Sea Ice Concentration Land The Need for Measurements The Forward Problem Over Land Empirical Approaches to Snow Depth A Final Comment on Passive Polarimetrv Further Reading ACTIVE MICROWAVES 221

8 Contents XXI 9.1 Principles of Measurement What is RADAR? Basic Radar Operation 9.2 The Generic Equations of Radar Performance The Radar Equation Range resolution 9.3 Radar Altimeters The Need for Altimeter Measurements Altimeter Geometry Instrumentation Echo Shape Analysis Range Ambiguity Accuracy of Height Retrievals Scanning Altimeters Calibration and Validation 9.4 Improving Directionality Sub-Beamwidth Resolution Synthetic Aperture Altimeters 9.5 Scatterometers The Need for Scatterometer Measurements General Operation Rain Radar Windscatterometers Polarimetric Scatterometers Further Reading IMAGING RADAR The Need for Imaging Radar Oceans Sea Ice Terrestrial Surfaces The Water Cloud Model for Vegetation Other Uses of Radar Imagery 264

9 xxii Introduction to Microwave Remote Sensing 10.2 What is an Image? Radar Image Construction Side-Looking Airborne Radar Ground Range resolution Azimuth Resolution Synthetic Aperture Radar (SAR) Aperture Synthesis: A Doppler Interpretation Aperture Synthesis: A Geometric Explanation Geometry vs Doppler SAR Focussing Radar equation for SAR Geometric Distortions in Radar Images Lay-over and Foreshortening Radar Shadow Motion Errors Moving Targets Operational Limits Ambiguities Coverage vs PRF Other SAR Modes ScanSAR Operation Spotlight Mode Working With SAR Images Speckle Speckle Statistics Speckle Filtering Geometric Correction Limitations of Geometric Correction SAR Data Formats Extracting Topography from SAR Images Stereo SAR Radargrammetry 302

10 Contents xxiii SAR Clinometry Further Reading INTERFEROMETRY The Need for Interferometric Measurements Principles of Interferometry Phase Measurements Application of Dual Systems Interferometry for Resolving Direction Passive Imaging Interferometry Radar Interferometry Interferometric Altimetry Interferometric SAR InSAR Viewing Geometries Interferometric Coherence Magnitude Decorrelation Summary of Decorrelation Practical DEM Generation InSAR Processing Chain Vegetation Height Estimation Single Frequency Dual-Frequency Polarimetric Interferometry and Multibaseline Interferometry SAR Tomography Differential SAR Interferometry Considerations and Limitations Atmospheric Water Vapour 339

11 xxiv Introduction to Microwave Remote Sensing 11.8 Permanent Scatterer Interferometry Along-Track Interferometry Further Reading 342 A 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 352 bibliography 353 index 357