1. Ali Cafer Gurbuz, Waymond R. Scott Jr. and James H. McClellan
LOCATION ESTIMATION USING A BROADBAND ELECTROMAGNETIC INDUCTION ARRAY
Ali Cafer Gurbuz, Waymond R. Scott Jr. and James H. McClellan
School of Electrical and Computer Engineering
Georgia Institute of Technology

2. Outline Introduction Method Examples Conclusions
Basis for Location Estimation
Dictionary
Orthogonal Matching Pursuit (OMP)
Examples
Simulated
Laboratory
Field
Conclusions
Scott, Georgia Tech
SPIE, April 2009

3. Array System Used for this Work
A broadband EMI system has been built
Single transmit and three receive coils
Broadband: 330 Hz to 90 kHz
High fidelity measurements
Battery Power
EMI Array Head
Broadband EMI Head
Broadband EMI System at Field Site
Scott, Georgia Tech
SPIE, April 2009 3
Scott, Georgia Tech
SPIE, April 2009

4. Introduction Broadband Electromagnetic Induction (EMI) Sensors
Effective for detecting buried metallic targets
Effective at discrimination of metallic targets
Compatible and often used with other subsurface sensors
This work is focused on estimating the locations of multiple metallic targets including their depth and cross ranges with an acceptable accuracy
Estimates are valuable in themselves making it easier to remediate targets
Estimates could significantly improve the results for the fusion of the EMI data with other sensor such as GPR
Scott, Georgia Tech
SPIE, April 2009

5. Outline Introduction Method Examples Conclusions
Basis for Location Estimation
Dictionary
Orthogonal Matching Pursuit (OMP)
Examples
Simulated
Laboratory
Field
Conclusions
Scott, Georgia Tech
SPIE, April 2009

6. Basis for Depth Estimation
Graph of the intensity of the down track response at a single frequency with depth as a parameter when the target passes under the center of the array
The relative size of the EMI response of the three array heads changes with depth
The shape of the down track response changes with depth
Shallow
Shallow
Shallow
Deep
Deep
Deep
Left Channel
Center Channel
Right Channel
Scott, Georgia Tech
SPIE, April 2009

7. Basis for Depth Estimation
Graph of the intensity of the down track response at a single frequency with cross range is a parameter when the target passes under the center of the array
The relative size of the EMI response of the three array heads change with depth
The shape of the down track response changes with depth
Far Right
Center
Far Left
Far Left
Far Right
Far Left or Right
Left Channel
Center Channel
Right Channel
Scott, Georgia Tech
SPIE, April 2009

8. How to use this info?
To use the information we followed a basis pursuit method:
Discretize the target space
Generate EMI target response model for each possible target space point, generating a dictionary of responses
Use orthogonal matching pursuit to extract the optimal representation of the received signal in terms of the dictionary elements finding the target location information
Scott, Georgia Tech
SPIE, April 2009

9. Dictionary Generation: EMI Model
Target is assumed to be infinitesimal and described by the magnetic polarizability tensor M
Magnetic fields calculated using the Bio-Savart law
Using reciprocity that the received voltage due to the target is
Scott, Georgia Tech
SPIE, April 2009

10. Dictionary Generation
Discritizing the target space and calculating the model data for each possible target location for any scan position of the EMI sensor generates a dictionary of responses
However generating the dictionary for 3D target localization increases the size of the dictionary making it unrealistic to work with it
For 1m3 volume with 1 cm resolution the dictionary would have 1 million columns !!!
Scott, Georgia Tech
SPIE, April 2009

11. Use Translational Symmetry
As the array scans targets having shifted y locations but the same cross range and depth values ,i.e., same x and z locations, result in shifted responses of each other in the receiver coils.
It is sufficient to create a dictionary for y = 0 cross range slice and use it to locate targets in 3D.
Scott, Georgia Tech
SPIE, April 2009

12. Orthogonal Matching Pursuit
Scott, Georgia Tech
SPIE, April 2009

13. Outline Introduction Method Examples Conclusions
Basis for Location Estimation
Dictionary
Orthogonal Matching Pursuit (OMP)
Examples
Simulated
Laboratory
Field
Conclusions
Scott, Georgia Tech
SPIE, April 2009

14. Simulated Scanning Example #1
A running scan is simulated
Horizontal line denotes the center line of the EMI array
Although target position estimates are done for the current measurements, (shown by green stars), they are not accepted (shown by red) until they fall in the acception region.
Acception region is taken as 25 cm behind of the center line of array.
The model effects of accepted targets are taken out of measurements for detecting future targets.
Scott, Georgia Tech
SPIE, April 2009

15. 3D Scanning Examples - 2
Scott, Georgia Tech
SPIE, April 2009

16. Experimental Laboratory Results
For the laboratory results, the EMI head is stationary and the target is scanned
Lessons the effects of nearby metal objects
Single Loop Z
Yaw
Three Loop
Pitch Y X
Five Degree-of-Freedom Non-metallic Positioning System
Broadband EMI Sensor
Scott, Georgia Tech
SPIE, April 2009

17. Example: Single Loop 22 AWG wire with a diameter of 31.8 cm
For the laboratory results, the EMI head is stationary and the target is scanned
x=17 cm, yaw=0, pitch=0, z = −8 cm to z = −20 cm with 1 cm increments
Scan y = −50 to y = 50 cm with 0.5 cm increments
Accurate Location estimated for all depths
A loop target model oriented in z direction is used for dictionary generation
Scott, Georgia Tech
SPIE, April 2009

18. Example: Single Loop 22 AWG wire with a diameter of 31.8 cm
For the laboratory results, the EMI head is stationary and the target is scanned
x=0 and 32 cm, yaw=0, pitch=0, z = −8 cm to z = −20 cm with 1 cm increments
Scan y = −50 to y = 50 cm with 0.5 cm increments
X = 2
X = 32
Scott, Georgia Tech
SPIE, April 2009

19. Example: AP Landmine Medium metal AP Landmine
For the laboratory results, the EMI head is stationary and the target is scanned
x=17 cm, yaw=0, pitch=0, z = −8 cm to z = −20 cm with 1 cm increments
Scan y = −50 to y = 50 cm with 0.5 cm increments
Accurate Location estimated until ̴ 15 cm depth
A loop target model oriented in z direction is used for dictionary generation
Scott, Georgia Tech
SPIE, April 2009

20. Example: AP Landmine Medium metal AP Landmine
For the laboratory results, the EMI head is stationary and the target is scanned
x=7 and 28cm, yaw=0, pitch=0, z = −8 cm to z = −20 cm with 1 cm increments
Scan y = −50 to y = 50 cm with 0.5 cm increments
X = 7
X = 28
Scott, Georgia Tech
SPIE, April 2009

21. Example: Triple Loop
Three loops of copper wire that are at right angles to each other: zr = 10.1, 50.2, and 172 kHz.
For the laboratory results, the EMI head is stationary and the target is scanned
x=17 cm, yaw=0, pitch=0, z = −8 cm to z = −20 cm with 1 cm increments
Scan y = −50 to y = 50 cm with 0.5 cm increments
Poor Location estimated for all depths
A loop target model oriented in z direction is used for dictionary generation
Scott, Georgia Tech
SPIE, April 2009

22. Field Data
The broadband array EMI system is scanned over the grid squares
Battery Power
EMI Array Head
Broadband EMI System at Field Site
Scott, Georgia Tech
SPIE, April 2009

23. Field Data Results
Measurements taken over an AP mine with the quadrapole array in the field.
Depth estimates for 6 different instances of an AP mine in the field
Scott, Georgia Tech
SPIE, April 2009

24. Conclusions and Summary
A promising location estimation method using electromagnetic induction array data is proposed.
Simulated, Laboratory and Field Data Results indicate that depth and cross range estimation of targets could be obtained within an acceptable accuracy
Future work requires modeling the target for generalization of the method
Scott, Georgia Tech
SPIE, April 2009

25. Questions
Scott, Georgia Tech
SPIE, April 2009