radar tunnel detection · underground tunnels present both military and homeland security threats:...

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s Carey Rappaport and Jose Martinez-Lorenzo ALERT Center of Excellence Northeastern University, Boston, MA ADSA-CBP 01, Boston, MA - June, 2018 Radar Tunnel Detection

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Page 1: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

s

Carey Rappaport and Jose Martinez-Lorenzo

ALERT Center of Excellence Northeastern University, Boston, MA

ADSA-CBP 01, Boston, MA - June, 2018

Radar Tunnel Detection

Page 2: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Challenges and Conclusions

Finding tunnels along border is hard: • Lots of terrain to cover • Variable depth • Randomly varying rough ground surface • Unknown soil dielectric constant • Lossy (moist) soils obscure signals • Attended sensors are expensive, unattended sensors are targets

There is hope: • Tunnels have distinctive feature of long aspect ratio • Tunnels are filled with known target material (air) • Airborne SL-SAR can scan region quickly • Underground focusing (UF) is essential for detection

UF-SL-SAR imaging is compelling for Mexican and Middle Eastern borders

Here’s Why…

Page 3: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access under high security facilities • Avoid security checkpoints (especially on the borders)

Near Otay Messa, CA (Sandy H, Getty Images 2006)

Tijuana, Mexico (David Maung, AP, 2004)

Height: 1.5 – 2 m

Width: 0.5 – 1 m

Length: 0.1 – 10 km

Problem formulation

Page 4: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Current methods

Most of the currently proposed solutions rely on land-based Ground Penetrating Radar (GPR)

Time consuming

Expensive

Trade-off between image quality & scanning time

Radio Frequency Tomography for Tunnel Detection [Lo Monte 2010]

Page 5: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Why Spotlight-SAR?

Synthetically focus for narrow illumination spots

Generate high resolution images

Scans large regions in short amount of time

Spotlight SAR [Natural Resources Canada 2005]

Page 6: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

System configuration and challenges

Penetration

Depth d10

= Distance for

the power to

drop by a factor

of 10 (-10 dB)

(19%wet)

(26%wet)

Penetration Depth v. Frequency for various dielectric materials

Page 7: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Multiple angles and frequencies for higher resolution: 128 frequencies from 50 MHz to 550 MHz

19 angles from -45 degrees to 45 degrees

Parametrize permittivity

Tunnel: 1 m x 1.5 m

Simulation configuration

Parameter: roughness height

Several angles and

several frequencies

Page 8: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Underground Focusing Considerations

Enhances Spotlight – SAR capabilities

Takes into account wave refraction assuming a flat surface

Needs estimation of soil characteristics

Image quality and tunnel detectability depend on soil properties

Underground media variation presents challenges

Transmitter Refraction point

Target

ε1

ε2

Page 9: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Non-dispersive sandy soil resolution: focal spot size

Refraction focusing at

underground point

y= 0.5 m y= 0 m

y= -4 m

y= -4 m

y= 0.5 m y= 0 m

Focusing at point on surface

Page 10: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Field Scattered by Rough Surface Imperfections / Tunnel: 550 MHz , -45 deg.

Magnitude Scattered No Tunnel

Transverse distance (m)

Depth

(m

)

Magnitude Scattered Tunnel

Transverse distance (m)

Depth

(m

)

Page 11: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Focused at 0.5m Focused at 0.5 m

Magnitude Total field No Tunnel

Magnitude Total field Tunnel

From 0.5 m to -9 m

Focused at 0 m Focused at 0 m Focused at -1 m Focused at -1 m Focused at -2 m Focused at -2 m Focused at -3 m Focused at -3 m Focused at -4 m Focused at -4 m Focused at -5 m Focused at -5 m Focused at -6 m Focused at -6 m Focused at -7 m Focused at -7 m Focused at -8 m Focused at -8 m Focused at -8 m Focused at -8 m

Range focusing dry sand: total field

Page 12: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Nominal Image Reconstruction

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 13: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Wavenumber Estimation

Case I: Non-dispersive dry clay soil Simulation: ε = 8 ε0 (1+0.01 i )

Imaging: parameter sweep

εr = [1,3,4, 6, 8, 10, 12, 14]

Roughness height sweep:

R = [0.1 0.2 0.3 0.4 0.5 0.6]

Case II: Lossy clay loam soil Simulation: ε = A.P. Hill firing point

Imaging: parameter sweep

Page 14: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Case I: Non-dispersive dry clay soil

Imaging with permittivity sweep

Page 15: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 1

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 16: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 3

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 17: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 4

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 18: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 6

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 19: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 8

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 20: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 10

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 21: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 12

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 22: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction with εr = 14

Magnitude of scattered field [dB scale]

Original geometry Tunnel

Page 23: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Case II: Lossy clay loam soil Imaging with permittivity sweep

Page 24: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Lossy, dispersive clay loam soil

Average

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 108

0.01

0.012

0.014

0.016

0.018

0.02

0.022

0.024

0.026

0.028

0.03

Frequency (Hz)

Co

nd

ucti

vit

y (

S/m

)

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 108

8.8

9

9.2

9.4

9.6

9.8

10

10.2

10.4

Rela

tive R

eal D

iele

ctr

ic C

on

sta

nt

Frequency (Hz)

Page 25: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Dispersive clay loam soil

y= 0.5 m y= 0 m y= -4 m

Focusing at point on surface

Refraction focusing at underground point

-25dB

-25dB

Page 26: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction: ε = 0.1 εhill

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Width (m)

Heig

ht (m

)

Page 27: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Width (m)

Heig

ht (m

) Image reconstruction: ε = 0.3 εhill

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Page 28: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Width (m)

Heig

ht (m

) Image reconstruction: ε = 0.8 εhill

Page 29: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Width (m)

Heig

ht (m

) Image reconstruction: ε = 1 εhill

Page 30: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Width (m)

Heig

ht (m

) Image reconstruction: ε = 2 εhill

Page 31: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Width (m)

Heig

ht (m

) Image reconstruction: ε = 4 εhill

Page 32: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Width (m)

Heig

ht (m

) Image reconstruction: ε = 8 εhill

Page 33: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Magnitude of scattered field [dB scale]

Original geometry Reconstruction Tunnel response

Width (m)

Heig

ht (m

) Image reconstruction: ε = 12 εhill

Page 34: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Roughness sweep: dry sandy soil

ε = 2.55 ε0 (1+0.01 i )

Page 35: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction: Rheight = 0.1 m

Magnitude of scattered field [dB scale]

Original geometry Tunnel Background

Page 36: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction: Rheight = 0.2 m

Magnitude of scattered field [dB scale]

Original geometry Tunnel Background

Page 37: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction: Rheight = 0.3 m

Magnitude of scattered field [dB scale]

Original geometry Tunnel Background

Page 38: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction: Rheight = 0.4 m

Magnitude of scattered field [dB scale]

Original geometry Tunnel Background

Page 39: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction: Rheight = 0.5 m

Magnitude of scattered field [dB scale]

Original geometry Tunnel Background

Page 40: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Image reconstruction: Rheight = 0.6 m

Magnitude of scattered field [dB scale]

Original geometry Tunnel Background

Page 41: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Underground Focusing Spotlight Synthetic Aperture Radar for low-loss soils (deserts):

Successful detection on non-dispersive sandy soil until surface roughness exceeds 0.5 m (for correlation length of 1 m)

Sufficiently high wave number estimate provides accurate tunnel detection

Wrong prediction of tunnel depth

Partial reconstruction of surface

Conclusions -- 1

Page 42: Radar Tunnel Detection · Underground tunnels present both military and homeland security threats: • Transit routes for trafficking drugs, people and weapons • Detonation access

Underground Focusing Spotlight Synthetic Aperture Radar for lossy soils:

Unsuccessful tunnel detection even with minimal surface roughness

Soil loss reduces target signal below surface clutter levels

Not suitable for tunnel detection with UF-SL-SAR

Conclusions -- 2

Acknowledgments: Gordon-CenSSIS NSF ERC Program (Award number EEC 9986821) and U.S. Dept. of Homeland Security (Award number 2008-ST-061-ED0001) The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Dept. of Homeland Security.