Multiple wavelength microwave-enhanced infrared thermography

• US 6,753,529 B2
• Filed: 07/02/2002
• Issued: 06/22/2004
• Est. Priority Date: 07/03/2001
• Status: Expired due to Fees

• Current Assignee: Northeastern University
• Original Assignee: Northeastern University
• Inventors: DiMarzio, Charles A., Sauermann, Gerhard O., Oktar, Taner, Rappaport, Carey M.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US10/189,340
• Publication Number:
  US 20030010919A1
• Time in Patent Office: 721 Days
• Field of Search: 250/341.6, 250/347, 250/341.1
• US Class Current: 250/341.6
• CPC Class Codes: F41H 11/12 Means for clearing land minefields; Systems specially adapted for detection of landmines
• CPC Class Codes: G01N 25/72 Investigating presence of flaws
• CPC Class Codes: G01V 8/005 operating with millimetre waves, e.g. measuring the black losey radiation

Abstract

A microwave-enhanced infrared thermography technique for detecting buried objects exploits varying phase shifts experienced by different-frequency microwave signals reflected from objects back toward the surface, the phase shifts resulting in different interference patterns and therefore different temperature distribution patterns near the surface. Respective infrared images of an area are captured prior to microwave heating, after a first heating with a first frequency, and after heating with a second frequency different from the first. Pairs of the images are subtracted to form temperature rise images showing patterns of temperature rise in the two cycles, and the temperature rise images are subtracted to form a difference image which is analyzed to identify characteristics indicating the presence of buried objects.

Claims

1. A method for detecting whether an object is buried beneath a target surface area of the ground, comprising:

1) in a first cycle;

a) capturing a first infrared image of the target surface area indicative of a first initial temperature distribution thereon;

b) directing a microwave signal of a first frequency at the target surface area and capturing a second infrared image of the target surface area indicative of a first heated temperature distribution thereon; and

c) subtracting the first infrared image from the second infrared image to form a first temperature rise image;

2) in a second cycle;

a) directing a microwave signal of a second frequency at the target surface area and capturing a third infrared image of the target surface area indicative of a second heated temperature distribution thereon, the second frequency differing from the first frequency by an amount effective to yield an acceptably high signal to noise ratio in a difference image to be calculated as part of the method; and

b) subtracting a fourth infrared image from the third infrared image to form a second temperature rise image, the fourth infrared image being indicative of a second initial temperature distribution of the target surface area at the beginning of the second cycle; and

3) subtracting the first temperature rise image from the second temperature rise image to obtain the difference image for processing to identify characteristics indicative of the presence of a buried object.

2. A method according to claim 1, wherein the first initial temperature distribution is a background temperature distribution existing prior to any microwave heating of the target surface area.

3. A method according to claim 1, wherein the second cycle is performed substantially immediately after the first cycle such that the second initial temperature distribution is substantially the first heated temperature distribution, and wherein the fourth infrared image used to calculate the second temperature rise image is the second infrared image captured in the first cycle.

4. A method according to claim 1, wherein the second cycle is performed sufficiently after the first cycle that thermal diffusion may cause the second initial temperature distribution to differ from the first heated temperature distribution, and further comprising capturing the fourth infrared image used to calculate the second temperature rise image at the beginning of the second cycle.

5. A method according to claim 1, further comprising one or more additional cycles, each additional cycle including (i) directing a respective microwave signal at the target surface area, (ii) capturing a respective heated infrared image of the target surface area indicative of a respective heated temperature distribution thereon, and (iii) subtracting a respective initial infrared image from the respective heated infrared image to form a respective temperature rise image, each initial infrared image being indicative of a respective initial temperature distribution on the surface of the target area, and further comprising using the additional temperature rise images in the calculation of the difference image.

6. A method according to claim 5, wherein each of the additional cycles uses a respective microwave frequency different from the respective microwave frequencies used in the other cycles.