Novel MultiAperture Imaging Systems

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Novel Multi-Aperture Imaging Systems

• Joseph C. Marron, Richard L. Kendrick,
• Thomas Hoft and Nathan Seldomridge
• Lockheed Martin Coherent Technologies
• 135 S. Taylor Ave.
• Louisville, CO 80027
• joe.marron_at_lmco.com
• R.L. Kendrick is with LM Advanced Technology
  Center in Palo Alto, CA.

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Presentation Outline

• Motivation for Multi-Aperture Active Imaging
• Technical Approach
• Experimental Results
• Four Aperture Combiner
• Extended Range Testing
• Conclusion

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Distributed Aperture Active Imaging
Imaging systems are advanced significantly by
incorporating array concepts into receivers and
transmitters
THEN
NOW
FUTURE

• Features
• Passive
• Segmented Primary
• Common Secondary

• Features
• Passive
• Segmented Primary
• Separate Secondaries
• Optical Combiner

• Features
• Active
• Segmented Primary
• Separate Secondaries
• Digital Combiner
• Also 3D and DE

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r -Space Image Formation
Source
OPD1
rs
y
x
r
z
OPD2
Object Surface
rd
Detector
Objects Complex 3D Reflectivity
r-Space Measurement
3D Fourier Kernel
Unit Vectors
"Three-Dimensional Lensless Imaging Using Laser
Frequency Diversity," J.C. Marron and K.S.
Schroeder, Applied Optics, 31, 255-262, 1992.
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3D Fourier Fill
Source
rs
Detector Array
Object Surface
rd
2D Detector Array
3D Fourier Transform
l
3D Image
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Resolution
2D Detector Array
3D Image
3D FFT
W
Dl
capable of microns
Z resolution
X,Y resolution
equivalent to lens of size W
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Synthetic Aperture Imaging Taxonomy
Data Space 3D (angle, angle, wavelength)
b
Image Space 3D (x,y,z)
l
a
y
z
x
3D Fourier Transform
3D Parameterized
3D Imaging
2D Imaging
Two-Wavelength Imaging
Coherent 2D Aperture

• Angular Aperture Synthesis
• Small speckle size
• Aperture fill detector arrays
• Increased resolution multi- aperture
• More wavelengths better 3D

Multi-Wavelength Imaging
Angle-Angle Data Slices
Angle-Angle Data Slice
Angle-Angle Data Slices
Phase-Difference Z(x,y) Image
Angle-Angle Projection Image
3D Image s(x,y,z)
Two-Receiver Interferometric SAR
Multi-Receiver Interferometric SAR
SAR Imaging

• Translational Aperture Synthesis
• Large speckle size
• Aperture fill airplane motion
• Increased resolution more bandwidth
• Multi-static better 3D

Range-Angle Data Slice
Range-Angle Data Slices
Range-Angle Data Slices
Range-Angle Projection Image
3D Image s(x,y,z)
Phase-Difference X(y,z) Image
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Distributed Aperture Active Imaging

• Features
• Large aperture receiver
• Fine-resolution imaging at extended range
• Modular system
• System simplified with modular approach
• Digital image formation
• Allows correction of optical misalignment errors
• Atmospheric Compensation
• Apply low-order correction to sub-apertures

Distributed Aperture Active System
Target
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Presentation Outline

• Motivation for Multi-Aperture Active Imaging
• Technical Approach
• Experimental Results
• Four Aperture Combiner
• Extended Range Testing
• Conclusion

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Technical Approach
1. Target flood illuminated coherent images
recorded by sub-apertures
2. Image reconstructed using digital imaging
methods
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Technical Approach
1. Target flood illuminated coherent images
recorded by sub-apertures
Transceiver Module
Detector


LO Spot
Array

Object Return
Field Stop

Pupil

(Intermediate Image)
Spatial Heterodyne Detection

• Coherent Image Recorded
• Complex-valued

Received Data
Fourier Transform
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Technical Approach
2. Image reconstructed using digital imaging
methods

• Digitally formed image sensitive to return-path
  turbulence
• Aberrations are determined directly using
  coherent data
• Auto-focus based on sharpness maximization
• Robust high-speed performance

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Autofocus Process
Initial Aberrated Image
Coherent Data
Amplitude
Recorded Data
Applied Phase Correction
Phase

• Iteration (25-30)
• Good Keep
• Bad Try again

Focused Image
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Presentation Outline

• Motivation for Multi-Aperture Active Imaging
• Technical Approach
• Experimental Results
• Four Aperture Combiner
• Extended Range Testing
• Conclusion

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Demonstration Experiments

• 4 aperture system

Sensor Table
Target Table
Laser
Collimator (places target at infinity)
Target
LO
Cam 2
Sub-Aperture Primaries (2 of 4)
Cam 1
LO
Sub-aperture Primaries
Sensor Table Front View
LO Fibers
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4 Aperture Modular System

• Extended Scene Images
• Object 1951 USAF Resolution Test Chart

Example Synthetic Pupil
Example Image

• Obscurations
• Collimator secondary
• Sub-aperture secondaries

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4 Aperture Modular System
1 sub-aperture, 1 realization
1 sub-aperture, 8 realizations
4 sub-apertures, 8 realizations
4 sub-aps, 8 realizations, filtered
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3D Imaging

• Base mode for coherent imaging
• Reflectivity image
• Also provides for 3D imaging
• Useful for ID, aimpoint selection
• Other discriminants follow

Reflectivity Image
Composite Image
3D Image (color-encoded)
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Table Mountain Experiments

• Demonstration of multi-aperture imaging over
  extended range (0.5 km)
• Extreme telescope misalignment
• Extreme atmospheric phase aberrations

Multi-Ap Telescope
Table Mountain Test Facility
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Table Mountain Experiments
Telescope Illuminator Laser
Target
Laser Height 40
Target Height 52
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Table Mountain Experiments

• Point target results

Corrected Image Strehl 0.63 (wavefront rms
0.11 waves)
Perfect System
Initial Image Strehl 0.20
Applied Phase
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Table Mountain Experiments

• Extended scene
• Motorcycle license plate at 0.5 km

Single Coherent Image
FFT
Raw Data
Object
20 images averaged To produce incoherent image
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Summary

• Distributed Aperture Active Imaging
• Allows fine resolution digital imaging
• Reduced volume, weight
• Features of Approach
• Digital image formation
• Corrects for optical misalignment errors
• Atmospheric compensation
• Apply low-order correction to sub-apertures
• Significant progress reported
• Laboratory and field demonstrations of imaging
  performance