Buried object detection in GPR images

• US 8,711,028 B2
• Filed: 08/26/2011
• Issued: 04/29/2014
• Est. Priority Date: 08/26/2010
• Status: Active Grant

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Inventors: Paglieroni, David W., Chambers, David H., Bond, Steven W., Beer, N. Reginald
• Primary Examiner(s): Sotomayor, John B
• Assistant Examiner(s): WINDRICH, MARCUS E
• Application Number:
  US13/219,456
• Publication Number:
  US 20130082860A1
• Time in Patent Office: 977 Days
• Field of Search: 342/22, 342/27, 342 25 R- 25 F
• US Class Current: 342/22
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat
• CPC Class Codes: G06N 99/00 Subject matter not provided for in other groups of this subclass

Abstract

A method and system for detecting the presence of subsurface objects within a medium is provided. In some embodiments, the imaging and detection system operates in a multistatic mode to collect radar return signals generated by an array of transceiver antenna pairs that is positioned across the surface and that travels down the surface. The imaging and detection system pre-processes the return signal to suppress certain undesirable effects. The imaging and detection system then generates synthetic aperture radar images from real aperture radar images generated from the pre-processed return signal. The imaging and detection system then post-processes the synthetic aperture radar images to improve detection of subsurface objects. The imaging and detection system identifies peaks in the energy levels of the post-processed image frame, which indicates the presence of a subsurface object.

Claims

1. A method performed by a computing device for generating a statistic for a down-track location from an original reconstructed image frame and a post-processed image frame, the original reconstruction image frame and the post-processed image frame being different representations of the same sample collected for the down-track location, the image frames having pixels with values, the method comprising:

calculating energy of the pixels in the original reconstructed image frame;

calculating a spot energy from the values of post-processed image frame pixels within a spot; and

setting the statistic based on a ratio of the spot energy to the pixel energy.

2. The method of claim 1 wherein the calculated energy of the pixels is the median of the values of the pixels in the original reconstructed image frame.

3. The method of claim 1 wherein the statistic is generated for each image frame in a sequence of image frames, peaks within the sequence are detected based on the generated statistic for each image frame, and subsurface object detection is based on the heights of those peaks.

4. The method of claim 3 wherein a spot that is less than a minimum area is too small to represent a subsurface object and a spot that is greater than a maximum area is too large to represent a subsurface object.

5. The method of claim 1 wherein the statistic is generated from each image frame in a sequence of image frames and the resulting statistics represents a times series of the statistic.

6. The method of claim 5 wherein each peak in the time series of statistics that exceeds a peak threshold in height and that is separated by a minimum number of statistics represents a subsurface object.

7. The method of claim 1 wherein the statistic is generated for each image frame in a sequence of image frames and the statistic is instantaneously self-detrending.

8. The method of claim 1 wherein a sequence of image frames is generated from return signals collected at a sequence of down-track locations from return signals acquired by receivers from ground-penetrating radar signals emitted by transmitters, the transmitters and receivers operating in a multistatic mode.

9. The method of claim 8 wherein the ground-penetrating radar signals are emitted into the ground and including determining whether an explosive device is buried based on analysis of statistics for the sequence of image frames.

10. A computer-readable storage device storing computer-executable instructions for controlling a computing device to detect an object within a sequence of image frames generated for down-track locations, each down-track location having a reconstructed image frame and post-processed image frame, the reconstructed image frame and the post-processed image frame representing the same image for a down-track location at the same sampling time, by a method comprising:

for each down-track location,

calculating energy of pixels in the reconstructed image frame for the down-track location;

calculating a spot energy from pixels of the post-processed image frame of the down-track location that are within a spot on the post-processed image frame; and

setting a statistic for the down-track location based on a ratio of the spot energy to the pixel energy; and

detecting presence of an object within the sequence of image frames based on a peak in the statistic for the down-track locations.

11. The computer-readable storage device of claim 10 wherein the calculated energy of the pixels is the median of the values of the pixels in the original reconstructed image frame.

12. The computer-readable storage device of claim 10 wherein a spot that is less than a minimum area is too small to represent an object and a spot that is greater than a maximum area is too large to represent an object.

13. The computer-readable storage device of claim 10 wherein an object is detected as present for each peak that exceeds a peak threshold in height and that is separated by a minimum number of down-track locations.

14. The computer-readable storage device of claim 10 wherein the statistic is instantaneously self-detrending.

15. The computer-readable storage device of claim 10 wherein a sequence of image frames is generated from return signals collected at the down-track locations by receivers from ground-penetrating radar signals emitted by transmitters.

16. A computing device for generating a statistic for a down-track location from a reconstructed image frame and a post-processed image frame, the image frames generated from return signals acquired at the down-track location at the same sampling time by receivers from ground-penetrating radar signals emitted by transmitters, the transmitters and receivers operating in a multistatic mode, comprising:

a component that calculates energy of pixels in the reconstructed image frame;

a component that calculates a spot energy from the values of post-processed image frame pixels within a spot; and

a component that sets the statistic for the down-track location based on a ratio of the spot energy to the pixel energy, the statistic for determining whether an object is buried in the ground.

17. The computing device of claim 16 wherein the calculated energy of the pixels is the median of the values of the pixels in the original reconstructed image frame.

18. The computing device of claim 16 wherein the statistic is generated for each image frame in a sequence of image frames, peaks within the sequence are detected based on the generated statistic for each image frame, and buried object detection is based on the heights of those peaks.

20. The computing device of claim 18 wherein the buried object is an explosive device.

19. The computing device of 18 wherein a peak of sufficient height in the statistics that is separated by a minimum number of statistics represents a buried object.