Detection of Obscured Targets: Signal Processing

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Detection of Obscured Targets Signal Processing

• James McClellan and Waymond R. Scott, Jr.
• School of Electrical and Computer Engineering
• Georgia Institute of Technology
• Atlanta, GA 30332-0250
• jim.mcclellan_at_ece.gatech.edu
• 404-894-8325

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Outline

• Introduction
• 3-D Quadtree Imaging
• GPR processing examples
• Location with Acoustic/Seismic Arrays
• Small Number of Receivers (moving)
• Cumulative Array strategy for imaging
• Accomplishments/Plans

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Three Sensor ExperimentSensor Adjustments and
Features

• Adjustable Parameters for all three sensors
• Frequency range
• Frequency Resolution
• Spatial Resolution
• Integration time/bandwidth
• Height above ground
• Location

• Possible Features for sensors
• EMI
• Relaxation frequency
• Relaxation strength
• Relaxation shape
• Spatial response
• GPR
• Primary Reflections
• Multiple Reflections
• Depth
• Spatial Response
• Seismic
• Resonance
• Reflections
• Dispersion
• Spatial response

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Multi-Resolution Processing
Features
Decision Process Exploit Correlation Training
GPR
Imaging
ID
Detect
Features
EMI
SigProc
Classify
Features
Seismic
Imaging
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Quadtree BackProjection

• Space-Time Domain Decomposition
• Image Patch Dividing and Sub-Aperture Formation
  (Virtual Sensor)
• Divide and Conquer Strategy
• Computational Complexity O(N2log2N)

Image Patch Dividing (Sub-Patch )
Sub-Aperture Formation (Virtual Sensor)
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GPR Processing

• Data taken in frequency domain with network
  analyzer 500 MHz to 8 GHz
• Imaging
• Quadtree
• Multi-resolution
• Approximate Backprojection
• 2-D, extend to 3-D
• Fast like w-k algorithms

Antenna Shape
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Detection and Region Elimination

• Purpose Distinguish regions consisting coherent
  scatterers, such as mines, from other regions
  consisting of only clutter.
• Detector exploits the fact that from stage to
  stage the energy for a coherent target increases
  relative to total energy while energy of clutter
  decreases.

Define the ratio of the energy in a sub-volume
Si1 to that in its parents Si
The probability of a target being present in
stage i1 is then given by Bayes Rule
Then apply a threshold test
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Quadtree Results
Experimental Data from the model mine
field Target A VS-50 AP Mine buried 1.3 cm deep
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3D Detection Volume
Synthetic Data 1 target at position X 13, Y
10, Z -10 Four quadtree stages, 1 cm step size
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Outline

• Introduction
• 3-D Quadtree Imaging
• GPR processing examples
• Location with Acoustic/Seismic Arrays
• Small Number of Receivers (moving)
• Cumulative Array strategy for imaging
• Accomplishments/Plans

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Seismic Sensor
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Home in on a Target

• Problem Statement
• Use a small number of source receiver positions
  to locate targets, i.e., landmines
• Minimize the number of measurements
• Three phases
• Probe phase use a tiny 2-D array (rectangle or
  cross)
• Find general target area from reflected waves
• Adaptive placement of additional sensors
• Maneuver receiver(s) to increase resolution
• RELAX/CLEAN recalculates for cumulative sensor
  array
• On-top of the target
• Verify the resonance

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Adaptive Sensor Placement
Target
Source
Probe Array
Probe Array finds general target area
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Wideband RELAX algorithm
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Surface Plot for Displays
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Examples using Sandbox Data

• Single source is used
• Only the Reverse wave is used in processing
• Or, passive listening for Buried structures
• Remove the Forward wave
• Prony analysis, or spatial filter
• Frequency range
• obtained from Spectrum Analysis of measured data
• Future work
• use RELAX to separate Forward and Reverse waves
• Cylindrical wave model

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Spectrum Analysis via Prony
TS-50 at 1cm
VS1.6 at 5cm
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Processing Examples

• Probe Phase
• Pick five sensors in a cross pattern
• Apply CLEAN/RELAX algorithm and plot the RELAX
  surface over a search grid
• Maneuver Phase
• Add one more sensor at a time
• Increase Aperture, or Triangulate
• Spatial resolution increases which narrows down
  the search area sfor the target

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TS-50 (1cm)
Source at (-20,50)
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Move Direction after PROBE Three likely
directions to move when adding one more sensor
Next Measurement
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Next Measurement
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2
3
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Further Probing of Direction-1
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Further Probing of Direction-3
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Another Probing of Direction-1
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On-Top
Sensor is placed at the Peak of Previous Step
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Yet Another Strategy
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Accomplishments

• Developed three sensor experiment to study
  multimodal processing
• Developed new metal detector and a radar
• Investigated three burial scenarios
• Showed responses for all the sensors over a
  variety of targets
• Demonstrated possible feature for
  multimodal/cooperative processing
• Developed new 3D quadtree strategy for GPR data
• Developed seismic experiments, models, and
  processing
• Improved experimental measurement by
  incorporating a Wiener filter
• Demonstrated reverse-time focusing and
  corresponding enhancement of mine signature
• Demonstrated imaging on numerical and
  experimental data from a clean and a cluttered
  environment
• Modified time-reverse imaging algorithms to
  include near field DOA and range estimates. The
  algorithms are verified for both numerical and
  experimental data with and without clutter.
• Modified wideband RELAX and CLEAN algorithms for
  the case of passive buried targets. The
  algorithms are verified for both numerical and
  experimental data with and without clutter.
• Used RELAX imaging to locate targets with
  cumulative maneuvering receivers.
• Developed a vector signal modeling algorithm
  based on IQML (Iterative Quadratic maximum
  Likelihood) to estimate the two-dimensional ?-k
  spectrum for multi-channel seismic data.
• Developed multi-static radar
• Demonstrated radar operation with and without
  clutter objects for four scenarios
• Buried structures
• Developed numerical model for a buried structure
• Demonstrated two possible configurations for a
  sensor

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Plans

• Three sensor experiment (Landmine)
• Incorporate reverse-time focusing and imaging
• Incorporate multi-static radar
• More burial scenarios based on inputs from the
  signal processors
• More/Stronger clutter
• Distribution of targets and clutter
• Close proximity between clutter and targets
• Look for more connections between the sensor
  responses that can be exploited for
  multimodal/cooperative imaging/inversion/detection
  algorithms
• Imaging/inversion/detection algorithms
• Extend 3-D quadtree algorithm to multi-static GPR
  data.
• Investigate the use of reverse-time ideas to
  characterize the inhomogeneity of the ground
• Investigate the time reverse imaging algorithm
  for multi-static GPR data.
• Investigate the CLEAN and RELAX algorithms for
  target imaging from reflected data in the
  presence of forward waves with limited number of
  receivers.
• Investigate joint imaging algorithms for GPR and
  seismic data.
• Buried Structures
• Experiments with multi-static radar
• Develop joint seismic/radar experiment
• Signal Processing