Synthetic aperture signal processing for high resolution 3D image reconstruction in the THz domain

1
Synthetic aperture signal processing for high
resolution 3D image reconstruction in the THz
domain
Signal Image Centre - RMA

• Marijke Vandewal, Roel Heremans and Marc Acheroy
• Royal Military Academy, Brussels

EUSIPCO, 24-28 August 2009
2
Outline

• Justification of synthetic aperture THz system
• Simulation of raw data
• Synthetic aperture imaging
• Performance analysis
• Conclusion future work

3
Introduction
Justification of synthetic Aperture THz system

• Non-Destructive Testing (NDT) techniques
• see-through capacity
• high spatial resolution (range azimuth)

• Conventional THz imaging techniques
• range resolution lt THz pulse width
• azimuth resolution lt ? and optics
• focusing depth

• Synthetic aperture imaging
• range resolution not altered
• azimuth resolution
• beam opening used as an advantage
• optics less demanding

4
Simulation of raw data
Synthetic Aperture Radar/Sonar
Raw data simulation of 9 point targets
1D Scanning geometry
stop
object
Along-track direction (m)
start
?az
?az
D
?az ? D/2
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Simulation of raw data
Extension towards THz
2D Scanning geometry
Raw data simulation of 2 point targets
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Simulation of raw data
Extension towards THz
Target positions
Raw data simulation of 2 point targets
Sensor position
Target position
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Synthetic aperture imaging
Reconstruction algorithm domains
time/space
range/Doppler
?
?
t?f
t
f
???
???
Fourier transform in range direction
t?f
-
wave number
?
?
t
f
Fourier transform in azimuth direction
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Synthetic aperture imaging
Reconstruction algorithms
Time/space domain
Wavenumber domain
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Synthetic aperture imaging
Time-domain reconstruction algorithm

• Very precise reconstruction
• High computational load need for parallel
  processing

10
Performance analysis
Theoretical azimuth resolution
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Performance analysis
Simulated azimuth resolution
TD reconstruction
12
Performance analysis
Comparison with wave number domain algorithm
TD reconstruction FD reconstruction
13
Performance analysis
Validity of simulated results

• Source and detector coherence
• Scanning precision
• Phase errors due to a varying propagation medium
• Trade-off wide beam opening and high SNR

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Conclusions Future work
Conclusions

• Comparison theoretical and simulated azimuth
  resolution
• Azimuth resolution dependence shown
• carrier frequency
• beam opening
• Practical limitations

Future work

• Application of TD and FD algorithm on real data
  using calibration test objects
• Extension of measurements to real aircraft parts