Multi-Sensor Measurements for the Detection of Buried Targetslcarin/Scott8.3.05.pdf2005/08/03 ·...
Transcript of Multi-Sensor Measurements for the Detection of Buried Targetslcarin/Scott8.3.05.pdf2005/08/03 ·...
Multi-Sensor Measurements for the Detection of Buried Targets
Waymond R. Scott, Jr. and James McClellanSchool of Electrical and Computer Engineering
Georgia Institute of TechnologyAtlanta, GA 30332-0250
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Outline
IntroductionThree Sensor ExperimentMulti-static RadarSeismic ArrayAccomplishments/Plans
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Multi-Sensor Cooperation/Adaptation
GPR
EMI
Seismic
Imaging
SigProc
Imaging
Features
Features
Features
DecisionProcess
ExploitCorrelation & Sensitivity
Feedback
Feedback
Controls
Controls
Controls
Controls
Controls
ControlsFrequency BandwidthFocusingRemote ImagingMeasurement Spacing
Frequency BandwidthMeasurement Spacing
Frequency BandwidthArray Elements UsedMeasurement Spacing
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Experimental Test BedDevelop a set of experiments to investigate the potential of multi-modal processing
Landmine (Three sensors/six modes)EMIGPR
• Bi-Static• Multi-Static
Seismic• Unfocused• Focused• Remote Detection
Buried Structure (Two sensors/four modes)GPR
• Bi-Static• Multi-Static
Seismic• Bi-Static• Multi-Static
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Outline
IntroductionThree-Sensor ExperimentMulti-static RadarSeismic ArrayAccomplishments/Plans
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Diagram of the Laboratory Model
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Three Sensor Experiment
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Three Sensor Experiment
Experimental Scenario #16 Mines> 20 Clutter objectsRelatively uniform distribution
Experimental Scenario #27 Mines> 25 Clutter objectsNon-uniform distribution
Experimental Scenario #3Non-uniform distribution of 7 Mines (2 AT, 5 AP) and 57 clutter objectsRock field surrounding AP mine and canAP mines and clutter objects grouped around and on top of AT mines
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Burial Scenario #1
1.8m by 1.8m Scan Region
Rocks (3 and4 cm deep)
Dry Sand(5cm deep)
MINESVS-2.2
(7cm deep)
TS-50(1.5cm deep)
w/ Nail
M-14(0.5cm deep)
VS-50(1cm deep)
PFM-1(1.5 cm deep)
VS-1.6(6.5cm deep)
SeismicSources
Cans (3 and2.5 cm deep)
AssortedMetal Clutter (2 to 4 cm deep)
Shells(4cm deep)
ThreadedRod(3.5cm deep)
Penny(5.5cm deep)
Nails(4cm deep)
Ball Bearing(3.5cm deep)
Shells(5.5cm deep)
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Comparison of ImagesSeismic Sensor
Image 30 dB Scale
GPR Sensor Energy Image of Migrated
Data (25 dB scale)
EMI SensorImage ( 90 dB scale)
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Outline
IntroductionThree-Sensor ExperimentMulti-static RadarSeismic ArrayAccomplishments/Plans
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Resistive-Vee AntennaWhy resistive-vee antenna?
Performs well in bistatic GPRsRadiates clean, short pulsesHas a low radar cross section
Reduces multiple reflections between the antenna and the ground
Geometry suitable in array applications
y
z
2 =
11.
43cm
A 2=
16.3
3cm
A p
w = 3mm
2 =
1.5
85m
ma
y ae1 = bz
y2 0 1 0 = + ( )c c z-z
y c c z zc z z
2 0 1 0
2 0
= + ( - ) + ( - )2
z = L0 0.2
L = 17.15cm
feed line(coplanar stripline)
Antenna designOptimized resistive loading profileOptimized arm shapeFrequency: up to 8GHz
Optimized Resistive Loading ProfileOptimized Arm Shape
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Resistive-Vee Antenna Implementation
Diagram of Measurement Setup
Comparison of Reflections
Photograph of Old Antenna
Photograph of New Antenna
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Multistatic GPR SystemComponents
Antenna array (2 Tx’s and 4 Rx’s)Placed in a dielectric frameProvides 8 bistatic apertures – aperture sizes are 12cm to 96cm with 12cm increment
Vector network analyzer (VNA)Provides a source & two samplers
Microwave switchesActivates/deactivates the antennas
3D positionerControl computer (not shown)Microwave absorber
Behind the array frameLowers the reflections from the positioner
Between the antennasLowers the reflection from the frame
Around feed cablesSuppresses radiation due to common mode currentHides electric conductors
VNA
Antenna array
Microwave absorber
3D positioner
Wet sand
Microwave switches
Picture of Multi-Static GPR
48cm 48cm
TTRRRR
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Multistatic GPR SystemVNA & antenna connection
VNA has one source and two samplers (A & B)T1 P1 T2 P2R1R2R3R4
VNA & switch operationResponse from 8 bistatic apertures are obtained by the following procedure:
1. Initialize all switches2. Obtain bistatic responses from T1-R1 and T1-R33. Throw internal switch4. Obtain bistatic responses from T2-R1 and T2-R35. Throw internal switch and external switches6. Obtain bistatic responses from T1-R2 and T1-R47. Throw internal switch8. Obtain bistatic responses from T2-R2 and T2-R4
Ext. Switch A sampler A
Ext. Switch B sampler B
Int. Switch source
Diagram of Multi-Static GPR
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Multistatic GPR SystemRaw bistatic responses
VNA sweeps 401 frequencies from 60MHz to 8.06GHz (20MHz increment)Control computer stores the raw responses in the frequency domainThe raw responses are calibrated after the measurement
Calibration
Free space response (FREE)Free space is simulated by pointing the array toward absorber-padded cornerSubtraction removes direct coupling in the system
Through response (THRU)Antenna ports are connected by a 5ft cableDivision removes distortion in the cables feeding the antenna
ij
ijjiji THRU
FREERTRT
−=
Picture of FREE Measurement
Picture of THRU Measurement
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Multistatic GPR SystemData acquisition
The array is scanned over 1.8m x 1.8m scan regionThe scan region is gridded into 91 x 91 points (∆x = ∆y = 2cm)
Per pointGPR obtains 8 bistatic responses at 401 frequency pointsInternal switch throw: 4 timesExternal switch throw: twiceTime: approximately 6 seconds
Per experimentData size: 8 (pairs) x 91 x 91 (points) x 401 (freq) x 8 (complex single) = 208 MBInternal switch throw: 33 124 timesExternal switch throw: 16 562 timesTime: approximately 14 hours
Picture of Scan Region
xy
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3D ExperimentsFree Space (calibration)
Spheres, Mines, Shapes, and No targetBuried targets (with clean surface and with surface covered by rocks)
No TargetsGrid of spheres (calibration)Grid of mines and clutterBuried structure
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Free Space Target Measurements -Setup
36.5cm
73 cm
xy
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Free Space Target Measurements -Targets
GT Plywood (38.5 x 46.5 x 1.84 cm)
11cm Shotput
1” Metal Sphere
TS-50
VS 1.6
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Multistatic Experiment in Free Space
Targets in Free Space A target is placed on top of 36.5cm high Styrofoam supportAntennas are elevated by 73cm from the ground
Radiation center is 90.8cm high from the groundGPR can obtain 6nsec of free space response before it sees the ground
Diagram of Experiment Setup
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Multistatic Experiment in Free Space
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
0
2
4
6
8
10
t, ns
ec
0
2
4
6
8
10
t, ns
ec
T1 R1 (12cm) T1 R2 (24cm) T1 R3 (36cm) T1 R4 (48cm)
T2 R1 (60cm) T2 R2 (72cm) T2 R3 (84cm) T2 R4 (96cm)
-60 dB
-80
-70
-90
-100
-60 dB
-80
-70
-90
-100
Bistatic Responses of 11.4cm (4.5”) Diameter Metal Sphere
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Multistatic Experiment in Free Space
ω – k migrationTarget: 11.4 cm (4.5”) diameter metal sphereApplied only to T1-R1 (12cm) response(Tx-Rx spacing is ignored)
Raw Response Migrated Image
Picture of Target
0 dB
-10
-5
-15
-25
0 dB
-10
-5
-15
-25
-20-20
2
4
3
5
7
6
t, ns
ec
2
4
3
5
7
6t,
nsec
-70 0-35 35 70y, cm
-70 0-35 35 70y, cm
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Multistatic Experiment in Free Space
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
0
2
4
6
8
10
t, ns
ec
0
2
4
6
8
10
t, ns
ec
T1 R1 (12cm) T1 R2 (24cm) T1 R3 (36cm) T1 R4 (48cm)
T2 R1 (60cm) T2 R2 (72cm) T2 R3 (84cm) T2 R4 (96cm)
-60 dB
-80
-70
-90
-100
-60 dB
-80
-70
-90
-100
Bistatic Responses of GT plywood
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Multistatic Experiment in Free Space
ω – k migrationTarget: 38.5cm x 46.5cm x 1.8cm GT shape plywoodApplied only to T1-R1 (12cm) response(Tx-Rx spacing is ignored)
Raw Response Migrated Image
Picture of Target
0 dB
-10
-5
-15
-20
0 dB
-10
-5
-15
-20
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Multistatic GPR ExperimentTargets in sand
Targets are buried 1cm – 13cm deep when measured from the surface of the sand to the top of the targetAntennas are elevated by 10cm from the sandIn cluttered-surface experiment:
Rocks are scattered over the scan regionRock density is empirically chosen to maximize the clutter effect
Sand with Clean Surface Sand with Cluttered Surface
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Multistatic GPR ExperimentBuried targets
Anti-tank mines: VS-1.6, VS-2.2, and TMA-5Anti-personnel mines: TS-50, PFM-1, M-14, and mine simulant Clutter objects: metal sphere, rock, crushed can, and nylon cylinder
Burial MapPicture of Targets
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Bistatic Responses of Landmine Targets at x = 0cm
Multistatic GPR Experiment
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
0
2
4
6
8
10
t, ns
ec
0
2
4
6
8
10
t, ns
ec
Clean-Surface Experiment
Cluttered-Surface Experiment
T1 R1 (12cm) T1 R3 (36cm) T2 R1 (60cm) T2 R3 (84cm)
T1 R1 (12cm) T1 R3 (36cm) T2 R1 (60cm) T2 R3 (84cm)
-60 dB
-80
-70
-90
-100
-60 dB
-80
-70
-90
-100
simulant
VS-2.2VS-1.6
PFM-1
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Landmine Scenario
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Landmine Scenario: Clean Surface
One Pair of antennas: T1R1 Four Pairs of antennas: T1R1, T1R2, T1R3, T1R4
Migrated Images: Time Domain
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Multistatic GPR ExperimentEnergy in Migrated Images Summed Over Depth: Time Domain
One Pair of antennas: T1R1
Four Pairs of antennas: T1R1, T1R2, T1R3, T1R4
One Pair of antennas: T1R1
Four Pairs of antennas: T1R1, T1R2, T1R3, T1R4
Shallow Depths Deep Depths
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Landmine Scenario: Rock Covered Surface
One Pair of antennas: T1R1 Four Pairs of antennas: T1R1, T1R2, T1R3, T1R4
Migrated Images: Time Domain
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Buried StructureTarget Location & Depth
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x = 0cm-cut
Buried Structure
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
-90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90 -90 -45 0y, cm
45 90
0
2
4
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10
t, ns
ec
0
2
4
6
8
10
t, ns
ec
R1 T1 R3 T1 R2 T2 R4 T2
R1 T1 R3 T1 R2 T2 R4 T2
0 dB
-20
-10
-30
-40
0 dB
-20
-10
-30
-40
rel. max.
rel. max.
Clean Scan
With-Rock Scan
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Buried Structure
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Buried Structure: Clean Surface
One Pair of antennas: T1R1 Four Pairs of antennas: T1R1, T1R2, T1R3, T1R4
Migrated Images: Time Domain
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Buried Structure: Rock Covered Surface
One Pair of antennas: T1R1 Four Pairs of antennas: T1R1, T1R2, T1R3, T1R4
Migrated Images: Time Domain
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Multistatic Inversion Issues
Back-Projected Images of 1” Metal Sphere
Input pulse: Diff. Gaussian; f0 = 2.5GHz
T1-R1 T2-R4
Responses of 4.5” Metal Sphere
T1-R1 T2-R4
Inversion Issues
Shape of response curvesThe response curves reduce to a hyperbola when
a = 0 (monostatic) orh >> a (far-field)
In this work, either a is significant or a > hBack-projected images
Images obtained by the typical delay-sum back-projection algorithm do not line up in depthSimple summation of back-projected images may not work
Complicated responses from a single target
Responses depending on the target shape, aspect angle, the illuminating waveform, etc.May be useful in identifying the target
Strong ground reflection needs to be removed before inversion
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Outline
IntroductionThree-Sensor ExperimentMulti-static RadarSeismic ArrayAccomplishments/Plans
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Ground Contacting Seismic Sensor Array Deployed on a Small Robotic Platform
Source Platform
Sensor Platforms
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Ground Contacting Seismic Sensor Array
Allowing contact with the ground makes is possible to construct robust and low-cost sensors arrays
Developed such a sensor using COTS componentsSensor weight (6 oz.) is much less than typical landmine detonation weights (more than 10 lbs. for AP landmines, much greater for ATlandmines)Array for this work
3 lines of 10 sensors1.35 inches between sensors in each line (fixed by sensor configuration)Variable spacing between lines
• Currently 4 inches (10 cm)• Maximum of 11 inches (29 cm)
Experiment shown with VS-1.6 AT Landmine Buried 5cm Deep
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ADXL103 Accelerometer
ICP Preamplifier
Pipe Insulation Foam Spring
Sorbothane Sensor Foot
19mm O.D. X 46 cm Long Aluminum Tube
SMB Connector
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Experimental Setup of Seismic Landmine Detection Measurements
3 by 10 Element Array of Ground-
Contacting Sensors
Seismic Source
VS-1.6 AT Landmine (5cm deep)
50 Tons of Damp, Compacted Sand
Scan Region of 2m by 2m
45 cm
174 cm
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Seismic Detection of VS-1.6 AT Landmine Buried 5cm Deep in Experimental Model
Landmine (22.2 cm diameter) buried 110 cm from first measurement location in 171 cm linear scan.
5 measurements with center line of sensor array along a line over the burial location.
Compressional, Rayleigh Surface, and ReflectedWaves.
Resonance of Landmine-Soil System.
Interactions of incident waves with buried landmine evident in measured data.
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AccomplishmentsDeveloped three sensor experiment to study multimodal processing
Developed new metal detector and a radarInvestigated three burial scenariosShowed responses for all the sensors over a variety of targetsDemonstrated possible feature for multimodal/cooperative processingDeveloped new 3D quadtree strategy for GPR data
Developed seismic experiments, models, and processing Developed optimal maneuver algorithm to locate targets with a seismic array Demonstrated reverse-time focusing and corresponding enhancement of mine signatureDemonstrated imaging on numerical and experimental data from a clean and a cluttered environmentModified 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. Developed a vector signal modeling algorithm based on IQML (Iterative Quadratic maximum Likelihood) to estimate the two-dimensional ω-k spectrum for multi-channel seismic data.
Developed multi-static radarDemonstrated radar operation with and without clutter objects for four scenariosInvestigated pre-stack migration imaging of multi-static data
Buried structuresDeveloped numerical model for a buried structureDemonstrated two possible configurations for a sensorMade measurement using multi-static radar
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PlansThree sensor experiment (Landmine)
Incorporate reverse-time focusing and imagingIncorporate multi-static radarMore burial scenarios based on inputs from the signal processorsLook for more connections between the sensor responses that can be exploited for multimodal/cooperative imaging/inversion/detection algorithms
Imaging/inversion/detection algorithmsUse reverse-time ideas to characterize the inhomogeneity of the groundInvestigate 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.Develop elimination and end-game strategies for seismic detection with a maneuvering arrayInvestigate joint imaging algorithms for GPR and seismic data.
Buried Structures & TunnelsExperiments with multi-static radarDevelop joint seismic/radar experimentSignal Processing