IMAGING WITH SYNTHETIC APERTURE RADAR

Transcription

1 ENGINEERING SCIENCES ; t rical Bngi.net IMAGING WITH SYNTHETIC APERTURE RADAR Didier Massonnet & Jean-Claude Souyris EPFL Press A Swiss academic publisher distributed by CRC Press

2 Table of Contents Acknowledgements Preface A THEORETICAL EMERGENCY KIT FOR SAR IMAGERY The propagation and polarization of electromagnetic waves Maxwell's Equations The polarization of electromagnetic waves Partially polarized waves In passing: the elegant algebra of the SU(2)-0 + (3) homomorphism The electromagnetic radiation of microwave antennas Introduction The electromagnetic radiation equation Resolving the electromagnetic radiation equation Antenna pattern, directivity and gain The radiation of planar antennas Array antennas SAR antenna technology Interaction between waves and natural surfaces Introduction Surface scattering Volume scattering Penetration properties of electromagnetic waves The effects of slope on radiometry Elements of signal processing Introduction Fourier series of real periodic functions Fourier transform 40 v vii

3 X IMAGING WITH SYNTHETIC APERTURE RADAR CHAPTER Properties of the Fourier transform (FT) Fourier transforms of standard functions Sampling real signals Sampling theorem (Shannon's theorem) The Fast Fourier transform (FFT) algorithm The two-dimensional Fourier transform 50 SAR PROCESSING: AT THE HEART OF THE SAR TECHNIQUE Introduction General principles of Synthetic Aperture Radar A different way of observing the Earth Range vision The three fundamental radar frequencies An intuitive geometrical approach to synthetic aperture Synthetic aperture, an analytic geometry formulation Frequency representation Phase distribution expressed in thefrequencydomain Non-Zero Mean Doppler Doppler locking Mean Doppler (or Doppler centroid) estimation Mean reduced Doppler estimation (integer part) Range migration Range processing Saturation effects Interference effects Motionless radar approximation SAR Synthesis algorithms A common preliminary step, range compression Time or 'naive' processing Range-azimuth or 'classic' processing An alternative technique, the Clk processor Subtle distortion, chirp scaling PRISME architecture, a multistage processing technique Unfocussed processing, a special case 90

4 TABLE OF CONTENTS XI A practical example of the unfocussed processing technique Another special case, deramping processing A radar processing technique without approximations System constraints Radar system design Timing constraints The different types of radar data Tricks for cheating nature Geometry characteristics A practical example of the effect of range on images Equations for geometric positioning Perpendicular radargrammetry Radargrammetry and interferometry Oblique radargrammetry Radar clinometry An introduction to super-resolution Radar processing and geometric specificity of bistatic data Direct echo Triangular resolution 115 CHAPTER 3 FROM SAR DESIGN TO IMAGE QUALITY Introduction Radar equation, Radar Cross Section (RCS) of a point target Loss terms Radar signature for extended targets - the backscatter Signal to noise ratio (SNR) of the radar-target link before SAR synthesis Modifying the SNR during SAR synthesis Point targets Extended targets Instrument Noise Equivalent cr (NEcx 0mst ) Energy cost for improving resolution Impact of image ambiguities on the NEa ' nst - total Range ambiguities 134

5 Xll IMAGING WITH SYNTHETIC APERTURE RADAR Azimuth ambiguities Combined processing of range and azimuth ambiguities Total NEa (NEcr 0 "") Volume of data generated onboard Telemetry data rate Source coding Calibration and corresponding image quality requirements Internal calibration External calibration Calibration requirements and expected scientific results Speckle noise and image statistics Physical origin Statistics of fully developed speckle Speckle noise: multiplicative nature and modeling Texture effect Speckle noise in multi-look images Speckle reduction filters The impulse response (IR) Range impulse response (RIR) Azimuth impulse response (AIR) Complex image spectrum, ISLR, PSLR, weighting effect Radiometric elements of Image Quality Estimating and analysing NEa otot Estimating the ambiguity level Radiometric resolution: Geometric elements of image quality Spatial resolution and pixel size Geometric distortion The image location Radar image interpretation Description of data Assessment of the Doppler spectrum Platform position 173

6 TABLE OF CONTENTS ХШ CHAPTER Saturation effects Directional effects Is it possible to fully characterize a radar instrument only from an image? 175 SAR INTERFEROMETRY: TOWARDS THE ULTIMATE RANGING ACCURACY Principles and limitations of radar interferometry A specific use for radar A brief history of interferometry Interferometry and the physical properties of radar images Phase difference between radar images Robustness of the phase signal in interferometry Limitations due to geometric and surface changes Eliminating systematic contributions Implementing interferometry processing Radar image co-registration Calculating phase differences between images Finishing tasks Application for topography Set of equations and error budget Eliminating measurement ambiguity Application for displacement measurement Set of equations and error budget Examples of use How slope effects limit interferometry Frequency interpretation of the slope effect Interpreting the results Typical signatures of different contributions Methods for improving interpretation Interferometry interpretation in practice Availability and mission perspectives Availability of archived radar data Availability of processing resources Principles of data selection Possibilities for future dedicated space missions. 213

7 XIV IMAGING WITH SYNTHETIC APERTURE RADAR CHAPTER Comparison of interferometry with other methods Comparison with optical stereoscopy for topographic measurement Comparison with GPS for measuring displacement Robustness of coherent processing when faced with ambiguities Permanent reflectors 226 SAR POLARIMETRY: TOWARDS THE ULTIMATE CHARACTERIZATION OF TARGETS Introduction Radar polarimetry: operating principle Timing analysis - impact on system design The scattering matrix The monostatic singularity - the backscattering matrix Target vector Standard forms of backscatter Odd-bounce (single, triple) scattering Even-bounce (double) scattering Diffraction or dipole mechanisms Polarization synthesis Polarimetrie signatures Characteristic polarization and Euler parameters The Huynen fork Coherent decomposition of the Polarimetrie measurement Decomposition into standard mechanisms - the group of Pauli matrices Algebraic decomposition: the Cameron approach Taking depolarization into account Stokes formalism and Mueller matrix Covariance matrix - coherence matrix Covariance matrix Coherence matrix Incoherent decomposition of Polarimetrie measurements Decomposition into polarization states: the Huynen approach 254

8 TABLE OF CONTENTS XV Decomposition into standard mechanisms - the Freeman approach Algebraic decomposition - The (H, a) approach Practical cases of Polarimetrie analysis Radiometric analysis Entropy analysis Average backscattering mechanism Synoptic representation of Polarimetrie information Future compact Polarimetrie systems Another idea: compact polarimetry and the JT/4 mode Merging polarimetry and interferometry: PolInSAR Interferometric coherence optimization Application to the inversion of vegetation height PolInSAR extensions Conclusion 273 Index 277