Synthetic Aperture Radar

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					                 강원대학교 자원개발연구소 세미나 – 2004년 4월 8일




Synthetic? Aperture? Radar!
      Systems and Signal Processing



              이훈열

            강원대학교
            지구물리학과
                                  Synthetic Aperture Radar – Systems and Signal Processing




Radarrr                                              rr rrr r rr r
 Radio Detection and Ranging
       WW II, England. Military use
       measure backscattered amplitude and distance to target
       High power, sharp pulse -> low power, FM-CW chirp signal


                  Navigation radar
                  Weather radar
                  Ground Penetrating Radar
                  Imaging radar


                  cf) LIDAR (Light detection and Ranging)
                           Synthetic Aperture Radar – Systems and Signal Processing




Imaging Radar
    Different Eyes
          microwave, UHF, VHF
          surface roughness and dielectric constant

    Microwave Ranging
          All-weather
          Cloud-free
          Side-looking

    Active System
          Day and night imaging
          independent of solar illumination
                         Synthetic Aperture Radar – Systems and Signal Processing




                     Aperture
Optics : Diameter of the lens or mirror. The larger the
aperture, the more light a telescope collects. Greater detail
and image clarity will be apparent as aperture increases.

       2.4m Hubble Space Telescope
       10m Keck, Hawaii
       16.4m VLT (Very Large Telescope), Chile
       50m Euro50
       100m OWL (OverWhelmingly Large T.)
OverWhelmingly Large Telescope
                        Synthetic Aperture Radar – Systems and Signal Processing




Real Aperture vs. Synthetic Aperture

• Real Aperture :
  resolution ~ Rλ/L

• Synthetic Aperture:
  resolution ~ L/2

  Irrespective of R
  Smaller, better?!
  - Carl Wiley (1951)
                                      Synthetic Aperture Radar – Systems and Signal Processing



ERS–1/2 SAR           Image Acquisition
L: 10 m, D: 1 m
Altitude: 785 km, sun-synchronous orbit
Ground Velocity: 6.6 km/s
Look Angle: Right 17-23 (20.355 mid-swath)
Slant Range: 845 km (mid-swath) Frequency: C- Band
(5.3GHz, 5.6 cm)
Footprint : 100 km x 5 km
Incidence Angle: 19  – 26  (23  mid-swath)
Sampling Rate: 18.96 MHz
Pulse duration: 37.1 s
Range gate: ~ 6000 s
Sampling Duration: ~ 300 s (5616 samples)
Inter-pulse period: ~ 600 s ( upto 10 pulses)
Pulse Repetition Frequency: 1700 Hz
Data Rate: 105 Mb/s (5 bits/sample)
                                      Synthetic Aperture Radar – Systems and Signal Processing




SAR Systems
Spaceborne SAR
SEASAT-A (USA, 1978), SIR-A (USA, 1981), SIR-B (USA, 1984), SIR-C/X-SAR (USA, Germany,
Italy, 1994), ALMAZ-1 (Russia, 1991-1993), ERS-1(EU, 1991-2000), ERS-2 (EU, 1995-),
JERS-1 (Japan, 1992-1998), Radarsat-1 (Canada, 1995-), SRTM (USA/Germany, 2000),
ENVISAT (EU, 2002),
RADARSAT-2 (Canada, 2005), PALSAR (Japan, 2004), LightSAR (US)*, TerraSAR (Germany)*,
MicroSAR(EU)*

Airborne SAR
TOPSAR (JPL, USA), IFSARE(ERIM/Intermap, USA), DO-SAR(Donier,Germany), E-SAR(DLR,
Germany), AeS-1(Aerosensing, Germany), AER-II (FGAN, Germany), C/X-SAR (CCRS,
Canada), EMISAR (Denmark), Ramses (ONERA, France), ESR (DERA, UK)

Planetary SAR
Magellan (US, 1990-1994), Titan Radar Mapper (US, 2004), Arecibo Antenna, Goldstone
antenna


* Under development
                                       Synthetic Aperture Radar – Systems and Signal Processing




SAR System Modes
 Target – the Earth or planets
 Vehicle – stationary, airborne, satellite, or spaceship
 Mode – monostatic and/or bistatic
 Carrier frequency – X, C, S, L, and/or P bands
 Polarisation – HH, VV, VH, HV (single-pol, dual-pol, full-pol)
 Imaging geometry – strip, scan, spot

 <examples>
      SIR-C/X-SAR: space shuttle, mono, L/C/X, full-pol.
      ERS-1/2, Envisat: Earth satellite, mono, C, VV.
      SRTM: space shuttle, mono/bistatic, C/X, HH/VV.
      Arecibo Antenna: planetary, stationary, mono/bi, multi-bands, multi-pol.
      Magellan, Cassini SAR: Venus and Titan, mono, S, HH.
      AIRSAR/TOPSAR: airborne, mono/bi, L/C/P, full-pol
                              Synthetic Aperture Radar – Systems and Signal Processing




ENVISAT
Launched 2002.2.28
C-band, Multpol, multi-mode
Data : Envisat Announcement of
Opportunity
                 Synthetic Aperture Radar – Systems and Signal Processing




Image Domain
                                            Range (R)
               5616 pixels, 100 km




                                               Azimuth (s)




                                               28,000 lines, 106 km
                                                   Synthetic Aperture Radar – Systems and Signal Processing




  Range Compression
            Linear Chirp Signal
  f (t )  exp[ 2i( f 0  0.5at )t ], 0  t  T                      Chirp autocorrelation Function




                                            Matched Filtering




                                                      For ERS-1/2,
                                                      Pulse duration (T): 37.1 s
                                                      Bandwidth : 15.5 MHz
                                                      Half power width of autocorrelation function: 0.065 s
                                                      Pulse Compression Ratio: 575 (ERS-1/2)
                                                      Ground Range Resolution: 12.5 m


Input           Range FFT                  Range Matched Filtering                        Range iFFT
                                   Synthetic Aperture Radar – Systems and Signal Processing




Range Migration                                  Flight Path




                         sc
                                             R
                                      Rc

                               R



                                                        Point Target




      R ( s )  Rc  (f Dc 2)( s  sc )  (f R 4)( s  sc ) 2

                          Linear                Quadratic
                       (Range Walk)         (Range Curvature)

                          Azimuth FFT
                                 Synthetic Aperture Radar – Systems and Signal Processing




Range Migration Compensation

              Range (R)
                          Rc                           Rc



Azimuth (s)




                sc




                                            After Range Walk Compensation




                          Range Migration
                                              Synthetic Aperture Radar – Systems and Signal Processing




Azimuth Compression
                                                             Synthetic Aperture
  Real Aperture




                                             Doppler Shift (Linear Chirp Pulse)
                                                                          2 V2          S      S
        /L                                  g ( s )  exp[ 2i ( f 0       s) s ],   s 
                                                                           R           2      2
 : wavelength
 L: Antenna length                                  For ERS-1/2,
                                                    Coherent Integration Time (S): 600 ms (5 km footprint)

Azimuth footprint width:         Matched            Bandwidth: 1260 Hz
                                 Filtering          Half power width of autocorrelation function: 0.8 ms
          5 km (ERS-1/2)
                                                    Pulse Compression Ratio: 756 (ERS-1/2)
                                                    Azimuth Resolution: 5 m


                           Azimuth Matched Filtering                                            Output
            SAR Focusing – Point Target
        azimuth
range




                    original         After range compression




                  After migration   After azimuth compression
         Synthetic Aperture Radar – Systems and Signal Processing



Southeast Cost of Spain
    ERS-2 (13km x 13km)




                                                 Descending,
                                                 Right Looking
                                 Synthetic Aperture Radar – Systems and Signal Processing




Geometric Distortion




      Terrain Imaging Geometry               Foreshortening




              Layover                             Shadow
        Synthetic Aperture Radar – Systems and Signal Processing



Scattering Mechanisms
                           Synthetic Aperture Radar – Systems and Signal Processing




 Rule of Thumb in SAR images
•Backscattering Coefficient

•Smooth – Black
•Rough surface – white

•Calm water surface – black
•Water in windy day – white

•Hills and other large-scale surface variations tend to
appear bright on one side and dim on the other.

•Human-made objects - bright spots (corner reflector)
•Strong corner reflector- Bright spotty cross (strong
sidelobes)
    Synthetic Aperture Radar – Systems and Signal Processing



청주공항 (ERS-2)
          Synthetic Aperture Radar – Systems and Signal Processing




Aleutian Volcanic Islands
        (ERS-1)
            Synthetic Aperture Radar – Systems and Signal Processing




Ship Wakes over the Bering Sea
 The Calving of Iceberg A-38
    (ERS-1 46 km x 28km)
             Synthetic Aperture Radar – Systems and Signal Processing




     대청호 ERS-1/2 SAR




Calm Water                     Rough Water
             Synthetic Aperture Radar – Systems and Signal Processing




    Ronne Ice Shelf, Antarctica
    The Calving of Iceberg A-38
(Radarsat ScanSAR 150km x 150km)
4-inch SAR onboard UAV
                          Synthetic Aperture Radar – Systems and Signal Processing




SAR Advanced Techniques
Radarclinometry: DEM from Shape-from-shading
(experimental)
Radargrammetry: DEM from stereo SAR image matching (m)
InSAR:
   Interferogram: DEM (cm)
   Coherence: statistical measurement of temporal and spatial
    decorrelation (cm)
DInSAR: surface displacement, penetration depth (mm).
Pol-SAR: Classification, segmentation
Pol-InSAR: measurement of scattering structure
SAR Tomography: 3D target distribution
             Synthetic Aperture Radar – Systems and Signal Processing




InSAR – Digital Elevation Model




             ERS-1/2 Tandem Interferogram
   InSAR Coherence Imagery
         Random Change Detection




InSAR Coherence Image     Optical Image
InSAR Coherence Imagery
      Seismic Survey Lines
Differential InSAR
    Earthquake
DInSAR
Volcano
  DInSAR
Glacier Velocity
   DInSAR
Land Subsidence
Planetary SAR
 Magellan to Venus
Planetary SAR
  Cassini to Titan
                 Synthetic Aperture Radar – Systems and Signal Processing




SAR Applications for Peace
   reconnaissance, survelliance and
  targetting
   target detection and recognition
   moving target detection
   navigation and guidence
- Sandia National Lab. 4-inch SAR
                        Synthetic Aperture Radar – Systems and Signal Processing




SAR Peaceful Applications
  Cartography – DEM, DTM
  Geology – Geological Mapping
  Seismology – Co-seismic displacement field
  Volcanology – Prediction of volcano eruption
  Forestry – Forest classification, deforest monitoring
  Soil Science – Soil moisture
  Glaciology – Glacier motion
  Oceanography – Ocean wave, wind, circulation, bathymetry
  Agriculture – Crop monitoring
  Hydrology – Wetland assessment
  Environment – Oil spill, hazard monitoring
  Archaeology – Sub-surface mapping
   Synthetic Aperture Radar – Systems and Signal Processing


Korean SAR