Technique for cancellation of elevated clutter for the detection of fixed and ground moving targets under trees

• US 7,095,358 B2
• Filed: 11/23/2004
• Issued: 08/22/2006
• Est. Priority Date: 11/23/2004
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Rosen, Robert A., Krikorian, Kapriel V.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/996,024
• Publication Number:
  US 20060109161A1
• Time in Patent Office: 637 Days
• Field of Search: 342 25 R- 25 F, 342 26 R- 26 D, 342 89-103, 342159-197, 342378-384
• US Class Current: 342/25.00B
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals

Abstract

A target is detected under a forest canopy or other elevated clutter where the target is obscured by the elevated clutter. Radar returns reflected from the target on the surface, combined with those from the elevated clutter are digitized. Motion compensation is performed for the radar returns with respect to the target to obtain a focused first synthetic aperture image of the target. Next, the radar returns are motion compensated with respect to the elevated clutter at various heights above the surface to obtain images of the elevated clutter. The elevated clutter within the images at the various heights above the surface is identified and coherently subtracted from the original synthetic aperture images.

Claims

1. A radar for acquiring a synthetic aperture image of a target on a surface, said target obscured by an elevated clutter at a height above said surface, said radar comprising:

a radar receiver mounted on a moving platform for illuminating said target obscured by said elevated clutter and for digitizing radar returns reflected from said target on said surface, and from said elevated clutter;

a computer for performing the steps of;

motion compensating said radar returns with respect to said target on said surface to obtain a focused first synthetic aperture image of said target on said surface;

motion compensating said radar returns with respect to said elevated clutter at one or more heights above said surface to obtain one or more focused clutter synthetic aperture images of said elevated clutter at each of said one or more heights;

identifying said elevated clutter within said one or more focused clutter synthetic aperture images at said one or more heights above said surface;

coherently subtracting said elevated clutter obtained from each of said one or more clutter synthetic aperture images from said radar returns thereby canceling said elevated clutter from said first synthetic aperture image to obtain an uncluttered image.

2. A radar system as described in claim 1 wherein said coherent subtracting is iterated one or more times by substituting said uncluttered image for said first synthetic aperture image.

3. A radar system as described in claim 2, wherein said radar combines radar returns obtained from a plurality of separate operating frequencies to generate said first synthetic aperture image and said clutter synthetic aperture images.

4. A radar system as described in claim 3 wherein a plurality of uncluttered images are examined to extract motion parameters and features of moving targets on said surface.

5. A radar system as described in claim 4 wherein said uncluttered images are thresholded with respect to a noise estimate of one or more of said uncluttered images.

6. A method using a radar for acquiring a synthetic aperture image of a target on a surface, said target obscured by an elevated clutter at a height above said surface, said method comprising the steps of:

illuminating said target obscured by said elevated clutter and said elevated clutter;

digitizing radar returns reflected from said target on said surface, and from said elevated clutter;

motion compensating said radar returns with respect to said target on said surface to obtain a focused first synthetic aperture image of said target on said surface;

motion compensating said radar returns with respect to said elevated clutter at one or more heights above said surface to obtain one or more focused clutter synthetic aperture images of said elevated clutter at each of said one or more heights;

identifying said elevated clutter within said one or more focused clutter synthetic aperture images at said one or more heights above said surface;

coherently subtracting said elevated clutter obtained from each of said one or more clutter synthetic aperture images from said radar returns thereby canceling said elevated clutter from said first synthetic aperture image to obtain an uncluttered image.

7. A method as described in claim 6 wherein said coherent subtracting is iterated one or more times by substituting said uncluttered image for said first synthetic aperture image.

8. A method as described in claim 7, wherein said radar returns are obtained from a plurality of separate operating frequencies to generate said first synthetic aperture image and said clutter synthetic aperture images.

9. A method as described in claim 8 wherein a plurality of uncluttered images are examined to extract motion parameters and features of moving targets on said surface.

10. A method as described in claim 9 wherein said uncluttered images are thresholded with respect to a noise estimate of one or more of said uncluttered images.