Ground Penetrating Radar: Impulse and Stepped Frequency

Transcription

1 Ground Penetrating Radar: Impulse and Stepped Frequency Carey M. Rappaport Professor Elect. and Comp. Engineering Northeastern University CenSSIS Workshop SW3, November 15, 2

2 Center for Subsurface Sensing and Imaging Systems (CenSSIS) A National Science Foundation Engineering Research Center Research and Industrial Collaboration Conference November 13-15, 2 Fundamentals of Underground Object Detection Carey M. Rappaport, Northeastern University This work was supported in part by the Engineering Research Center Program of the National Science Foundation under award number EEC

3 Two Main Types of GPR Impulse Short time excitation Measure travel time to/from target Gate out ground clutter Stepped Freq. (also FMCW) Measure magnitude and phase of each frequency Combine multiple frequencies Analyze spectrum for resonances Use multiple views to image

4 Receiver/Transmitter Configurations Monostatic Single Xmit., same Rec. T/R target Bistatic Pair of Xmit./Rec. T target R Multistatic Single Xmit. With many Recs. T target R R Multiple Xmit. With single Rec. R R

5 Geo-Centers Vehicle Mounted Mine Detection (VMMD) System (1997) IR Camera IR Camera EMI Array

6 Sensor Deployed at YPG (1999) Mast Mounted Equipment GPR Antenna & Electronics GPS/Inertial Positioning System 13 m Trailer Equipment Operator Workstation Data Collection/Control Computer Power Supply & Test Equipment

7 Multistatic GPR Array at CRREL Fall 2 transmit array receive array computer controlled scanner

8 Shape Determination of Buried Non-Metallic Targets by Multiple Single-Frequency Observations Sandy soil: ε s = 2.5, σ s =.1 Target: ε m = 2.9, σ m =.4 Circular Target Square Target Air 2 cm Air 2 cm Soil d cm Soil d 1 cm 6 cm 6 cm 1 cm 8 cm 8 cm

9 Different Buried Test Target Shapes square circle diamond Height (cm) star blob Horizontal Position (cm)

10 Scattered Field - Real Part 2 square 2 circle 2 diamond Height (cm) star blob Horizontal Position (cm) MHz, depth = 5 cm

11 Scattered Field - Real Part 2 square 2 circle 2 diamond Height (cm) star blob MHz, depth = 5 cm Horizontal Position (cm)

12 Surface Field - Magnitude 5 MHz, depth = 5cm 1 MHz, depth = 5cm.4.5 square.35.4 circle diamond star Intensity.3.25 square circle diamond star blob blob Horizontal Position (cm)

13 Height (cm) Scattered Field - Aspect Ratio Dependence Circle, r = 5.64 cm x 13.3 cm x 2 cm Horizontal Position (cm) x 7.5 cm x 1 cm x 5 cm x 4 cm x 2.5 cm Sandy Soil ε = 2.5, σ =.1 freq = 5 MHz depth = 5 cm

14 Surface Scattering Clutter Increases with Frequency. Example: 4 GPR Frequencies, PRCL 1% moisture, 1.4 g/cc density Depth (cm) Air Soil Non-Metallic Target Transverse Position (cm)

15 Mine scattered field: smooth surface Depth (cm) Depth (cm) Transverse Position (cm) Scattered field: rough surface only Transverse Position (cm) 48 MHz Amplitude Relative to Incident Amplitude Relative to Incident Scattered field: rough surface with mine Depth (cm) Depth (cm) Transverse Position (cm) Mine scattered field: rough surface Transverse Position (cm) Amplitude Relative to Incident Amplitude Relative to Incident

16 Depth (cm) Depth (cm) Mine scattered field: smooth surface Transverse Position (cm) Scattered field: rough surface only Transverse Position (cm) 96 MHz Amplitude Relative to Incident Amplitude Relative to Incident Scattered field: rough surface with mine Depth (cm) Depth (cm) Transverse Position (cm) Mine scattered field: rough surface Transverse Position (cm) Amplitude Relative to Incident Amplitude Relative to Incident

17 Depth (cm) Depth (cm) Mine scattered field: smooth surface Transverse Position (cm) Scattered field: rough surface only Transverse Position (cm) 192 MHz Amplitude Relative to Incident Amplitude Relative to Incident Scattered field: rough surface with mine Depth (cm) Depth (cm) Transverse Position (cm) Mine scattered field: rough surface Transverse Position (cm) Amplitude Relative to Incident Amplitude Relative to Incident

18 Depth (cm) Depth (cm) Mine scattered field: smooth surface Transverse Position (cm) Scattered field: rough surface only MHz Amplitude Relative to Incident Amplitude Relative to Incident Scattered field: rough surface with mine Depth (cm) Transverse Position (cm) Transverse Position (cm) Transverse Position (cm) Depth (cm) Mine scattered field: rough surface Amplitude Relative to Incident Amplitude Relative to Incident

19 2D SAMM Scattering from Circular Cylinder in Different Soils at 3 GHz AIR DRY SAND BOSNIAN SOIL Surface Depth AIR DRY SAND BOSNIAN SOIL TNT mine, f=3ghz, R=5cm, d=5cm, normally-incident plane wave

20 2D SAMM Scattering from Elliptical Cylinder in Different Soils at 3 GHz 12 mode families centered at mine, image E z : AIR E z : DRY SAND E z : BOSNIAN SOIL SAMM v. FDFD: 1.73% max error.34% av. error SAMM v. FDFD: 1.64% max error.25% av. error SAMM v. FDFD: 6.13% max error.75% av. error TNT mine: a=5cm, b=3 cm, d=5cm, normally-incident plane wave

21 Relative Amplitude Impulse GPR Measured Time Signals LLNL MIR Transmitted Pulse Time (ns) Measured Incident Pulse Geo-Centers TEMR Transmitted Pulse Time (ns)

22 Outdoor Measurements at NEU Dedham Test Track with Dry Loam / Vegetation

23 Ground-Penetrating Radar: Air Shot Transmitter Front Receivers Rear Receivers

24 Ground-Penetrating Radar Parabolic reflector antenna for forwarddirected plane wave Four detectors for back-scattered radiation High-bandwidth (3GHz) pulsed sources

25 Mine Target Placement Map of Experimental Test Track Cross-Track Al EM-6 EM-6 EM-6 VS-5 VS-5 VS-5 PMN Al Down-Track EM-6: Cylindrical, 15mm diameter, 5 mm high. VS-5: Cylindrical, 9mm diameter, 45mm high, plastic cased. PML: Cylindrical, 112mm diameter, 56mm high, plastic/bakelite/rubber. Northeastern University Dedham Test Track

26 Measured Signals at the Receivers Time Step Ground Reflection Direct T/R signal Down Track Position (in.)

27 Data Analysis Remove soil clutter from the total field to obtain mine signals Ideal ground signal Total average ground signal Moving average ground signal Evaluate the performance of different receivers. Synchronize the mine signals at different receivers to obtain strong mine signals.

28 Time Delay Focusing

29 Mine Signals Synchronization and Summation Left Front Right Front Left Rear Right Rear Depth 26 Depth 27 + Amplitude Threshold 2 Front Receivers Depth 28 Depth 29 + Amplitude Threshold 2 Rear Receivers + Amplitude Threshold 3 Four Receivers

30 Mine Signals

31 Summation of Four Receivers Relative Amplitude Down-Track (inches)

32 Forward-Looking AP Array GPR: Operational Configuration

33 Rough Sand Surface Testing at LLNL

34 Processed Signal from Non-Metallic Antipersonnel Mine Buried 1 inch Deep in Dry Sand with Rough Ground Surface Depth Rough Ground Surface Mine Anomaly Cross Track Position

35 Factors that Effect Performance Mines are of different types. Mine burial depth and orientation vary. Soil moisture and ground surface roughness change along the track. Radar pulse width and sensing time window are limited.

36 Summary GPR is readily available modality GPR sensors are available in impulse and stepped frequency modes Multistatic GPR can provide much more information than monostatic GPR can used to measure size/shape/resonance of target Ground surface clutter is major uncertainty Small contrast differences makes detection/ imaging more challenging