System for detecting man-made objects using polarimetric synthetic aperture radar imagery with error reduction and method of use

• US 10,436,897 B2
• Filed: 02/03/2017
• Issued: 10/08/2019
• Est. Priority Date: 12/08/2014
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Inventors: Ranney, Kenneth Irving, Wong, David Chun, Ton, Tuan That
• Primary Examiner(s): Akonai, Olumide Ajibade
• Application Number:
  US15/423,723
• Publication Number:
  US 20180052229A1
• Time in Patent Office: 977 Days
• CPC Class Codes: G01S 13/86 Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
• CPC Class Codes: G01S 13/867 Combination of radar systems with cameras
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• CPC Class Codes: G01S 13/9027 Pattern recognition for feature extraction
• CPC Class Codes: G01S 13/9076 Polarimetric features in SAR
• CPC Class Codes: G01S 7/024 using polarisation effects in waveguides H01P1/165; for aerials H01Q, e.g. H01Q15/22, H01Q15/24, H01Q19/195
• CPC Class Codes: G01S 7/025 involving the transmission of linearly polarised waves
• CPC Class Codes: G01S 7/292 Extracting wanted echo-signals
• CPC Class Codes: G01S 7/412 based on a comparison between measured values and known or stored values

Abstract

A system for determining the location of a man-made object based upon symmetry of the object comprising a receiver configured to receive radar signals comprising cross-polarized and co-polarized responses; at least one processor configured to combine the horizontal-horizontal polarimetric responses and vertical-vertical polarimetric responses to form co-polarimetric images and operate on one or both of the vertical-horizontal polarimetric responses and horizontal-vertical polarimetric responses to form cross-polarized images; the at least one processor configured to process the co-polarized and cross-polarized images to locate areas of interest containing a maximum in the co-pol image and a null state in the co-pol image indicating the potential detection of a man-made object; the at least one processor being configured to filter data using buffer regions and/or skipping of pixels in the vicinity of an area of interest. A method for detection of man-made objects is also disclosed.

Claims

1. A system for determining the location of a man-made object based upon symmetry of the object comprising:

a receiver configured to receive radar signals comprising cross-polarized and co-polarized responses, the co-polarized responses measured either by transmitting and receiving both horizontally polarized waves (horizontal-horizontal) or by transmitting and receiving both vertically polarized waves (vertical-vertical);

the cross-polarized responses measured by either transmitting horizontally polarized waves and receiving vertically polarized waves (horizontal-vertical) or by transmitting vertically polarized waves and receiving horizontally polarized waves (vertical-horizontal);

at least one processor, the at least one processor configured to process horizontal-horizontal co-polarimetric (co-pol) data, vertical-vertical co-polarimetric data, and one or both of the vertical-horizontal cross-polarimetric data and horizontal-vertical polarimetric data to form co-polarized images and cross-polarized images;

the at least one processor configured to process the co-polarized and cross-polarized images to locate areas of interest containing a maximum in the co-pol image and a null state in the cross-pol image indicating the potential detection of a man-made object;

the at least one processor being configured to filter data using buffer regions in the vicinity of an area of interest to reduce error.

2. The system of claim 1 wherein the at least one processor is configured to perform a summation operation on the pixels in the vicinity of an area of interest in the cross-polarized image and normalize the summation total by dividing by the number of pixels in the area summed to obtain a value indicative of the normalized intensity of the background;

and wherein the at least one processor is configured to perform a summation operation on the pixels in an area of interest in the cross-polarized image and normalize the summation total by dividing by the number of pixels in the area of interest indicative of the normalized intensity of the area of interest; and

wherein the at least one processor operates to divide the normalized intensity of the area of interest by the normalized intensity of the background to obtain a value indicative of the presence of a man-made object.

3. The system of claim 1 wherein the at least one processor is configured to perform a summation operation on the pixels in the vicinity of an area of interest in the co-polarized image and normalize the summation total by dividing by the number of pixels in the area summed to obtain a value indicative of the normalized intensity of the background;

and wherein the at least one processor is configured to perform a summation operation on the pixels in an area of interest in the co-polarized image and normalize the summation total by dividing by the number of pixels in the area of interest indicative of the normalized intensity of the area of interest; and

wherein the at least one processor operates to divide the normalized intensity of the area of interest by the normalized intensity of the background to obtain a value indicative of the presence of a man-made object.

4. The system of claim 1 wherein the at least one processor is configured to compute a spatial average and divide the spatial average by the intensity of the background and wherein the at least one processor is configured to reduce the value of pixels in an area of interest using a normalization process to thereby reduce effects of background and wherein the at least one processor determines the intensity of the background using the pixels surrounding the area of interest and calculating an average pixel value of the surrounding pixels.

5. The system of claim 4 wherein the spatial average is computed using the equation:

6. The system of claim 5 wherein the at least one processor determines the effect of background pixels in the cross polarimetric image after skipping a number of pixels m using the equation:

7. The system of claim 6 wherein for each pixel in the cross-pol image the at least one processor calculates the contrast between the pixel under test and any high intensity values the surrounding pixels by calculating the cross image contrast using the equation:

8. The system of claim 7 wherein the at least one processor is configured to incrementally select pixels under test, determine the spatial average, determine the background intensity, use the corresponding pixel under test in the filtered co-polarimetric image and divide by the ratio of the spatial average to the intensity of the background to compile a list of statistical values indicating the likelihood of a manmade object, and compare the statistical value to the correlated value of corresponding pixel under test in the co-polarimetric image and wherein a large value for the pixel under test in the co-polarimetric image is indicative of a manmade object.

9. The system of claim 8 wherein the at least one processor is configured to determine whether the reciprocal of the ratio of the statistical value to the correlated value of corresponding pixel under test in the co-polarimetric image is greater than 6 dB to indicate the presence of a man-made object.

10. The system of claim 1 wherein the polarimetric images are polarimetric SAR images, and wherein the horizontal-horizontal polarimetric images, the vertical-vertical polarimetric images, and one or both of the vertical-horizontal polarimetric images and horizontal-vertical polarimetric images are co-registered SAR images, and wherein a location in each of the images has a corresponding location in the other co-registered SAR images.

11. The system of claim 9 wherein the at least one processor is configured to determine within an area of interest if a pixel under test intensity differs from the pixels in the vicinity by at least 15 dB in order to determine the pixel location of the cross-range coordinate determinative of the left-right point of symmetry.

12. A method for determining the location of a man-made object comprising the following steps, not necessarily in order;

inputting image data comprising four co-registered polarimetric SAR images of a common scene;

the four co-registered polarimetric images comprising horizontal-horizontal, horizontal-vertical, vertical-vertical and vertical-horizontal polarimetric images, the inputted image data comprising pixel values representing the polarimetric SAR images, a location in each of the four co-registered SAR images having a corresponding location in the other three co-registered SAR images;

each of the four co-registered SAR images being inputted into at least one processor;

the at least one processor being configured to calculate a statistic indicating the likelihood that a manmade object is present by selecting a plurality of pixels under test and using at least one processor;

determining the intensity of the background for the pixels under test by skipping a predetermined number of cross-range cells on either side of a pixel under test in the cross-pol image to calculate a background average for pixels on either side of the pixel under test;

spatial averaging at a plurality of pixel locations in the vicinity of the pixel under test to determine the background average intensity for the pixel under test;

comparing the intensity of the pixel under test with the background intensity to determine potential man-made objects.

13. The method of claim 12 wherein determining the intensity of the background comprises skipping a predetermined number M pixels for each pixel in the filtered cross-pol image using the equation:

14. The method of claim 12 wherein the spatial averaging comprises utilizing the complex magnitude of each component image pixel, thereby enabling the exploitation of spatial averaging for speckle reduction, and wherein the processor spatial averages the pixels using the equation:

20. The system of claim 13 wherein the at least one processor performs spatial averaging at a plurality of pixel locations using the equation

15. A system for determining the location of a man-made object based upon symmetry of the object comprising:

a receiver configured to receive radar signals comprising cross-polarized and co-polarized responses and cross pol polarimetric images;

at least one processor, the at least one processor configured to combine the horizontal-horizontal polarimetric images and vertical-vertical polarimetric images to form co-polarimetric images and operate on one or both of the vertical-horizontal polarimetric images and horizontal-vertical polarimetric images to form cross-polarized images;

the at least one processor configured to process the co-polarized and cross-polarized images to locate pixels of interest containing a maximum intensity in the co-pol image and a null state in the cross-pol image indicating the potential detection of a man-made object;

the maximum intensity and null state being determined by comparing the pixels of interest with pixels in the vicinity of the pixels of interest to obtain relative intensity values;

the at least one processor refining the evaluation of pixels in the vicinity of pixels of interest by using spatial averaging at a plurality of pixel locations in the vicinity of the pixels of interest and

the at least one processor configured to skip a predetermined number pixels on either side of the pixel or pixels of interest before calculating the background average in order to diminish the effects of noise.

16. The system of claim 15 wherein the at least one processor skips a predetermined number pixels on either side of the pixel or pixels of interest in a filtered cross-polarimetric image according to the equation:

17. The system of claim 16 wherein the at least one processor is configured to perform a summation operation on the pixels in the vicinity of an area of interest in the PMOD image and normalize the summation total by dividing by the number of pixels in the area summed to obtain a value indicative of the normalized intensity of the background;

and wherein the at least one processor is configured to perform a summation operation on the pixels in an area of interest in the PMOD image and normalize the summation total by dividing by the number of pixels in the area of interest indicative of the normalized intensity of the area of interest; and

wherein the at least one processor operates to divide the normalized intensity of the area of interest by the normalized intensity of the background to obtain a PMOD image value indicative of the presence of a man-made object.

18. The system of claim 17 wherein the at least one processor is configured to perform a summation operation on the pixels in the vicinity of the pixels of interest in the co-polarized image and normalize the summation total by dividing by the number of pixels in the area summed to obtain a value indicative of the normalized intensity of the background;

and wherein the at least one processor is configured to perform a summation operation on the pixels in an area of interest in the co-polarized image and normalize the summation total by dividing by the number of pixels of interest to obtain a normalized intensity of the pixels of interest; and

wherein the at least one processor operates to normalize intensity of the pixels of interest by the normalized intensity of the background to obtain a value indicative of the presence of a man-made object.

19. The system of claim 18 wherein the at least one processor is configured to perform a summation operation on the pixels in the pixels in the vicinity of an area of interest in the cross-polarized image and normalize the summation total by dividing by the number of pixels in the area summed to obtain a value indicative of the normalized intensity of the background;

and wherein the at least one processor is configured to perform a summation operation on the pixels in an area of interest in the cross-polarized image and normalize the summation total by dividing by the number of pixels in the area of interest indicative of the normalized intensity of the area of interest; and

wherein the at least one processor operates to divide the normalized intensity of the area of interest by the normalized intensity of the background to obtain a value indicative of the presence of a man-made object and wherein the at least one processor multiplies the normalized summations on the pixels in the vicinity of an area of interest for at least two of the PMOD image, the cross-polarized image and the co-polarized image to provide an enhanced indication of the presence of a man-made object.