Synthetic Aperture focusing techniques

• US 20080297405A1
• Filed: 04/07/2008
• Published: 12/04/2008
• Est. Priority Date: 04/06/2007
• Status: Abandoned Application

• Current Assignee: Board of Trustees of The University of Illinois
• Original Assignee: Board of Trustees of The University of Illinois
• Inventors: Do, Minh N., Morrison, Robert L. JR., Munson, David C. JR.
• Application Number:
  US12/080,927
• Publication Number:
  US 20080297405A1
• Time in Patent Office: Days
• US Class Current: 342/25.00F
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals

Abstract

The present application describes an apparatus that includes a radar antenna device to acquire synthetic aperture radar data, radar receiver and transmitter equipment coupled to the radar antenna device, and a synthetic aperture radar processing device in communication with the radar receiver and transmitter equipment. This processing device includes a processor structured to process the synthetic aperture radar data, which is representative of a defocused image. The processor is further structured to define an image processing constraint corresponding to an image region expected to have a low radar return and generate one or more output signals as a function of the image processing constraint and the data. The one or more output signals are representative of a more focused form of the defocused image.

Claims

1. A method, comprising:

acquiring synthetic aperture radar data representative of a defocused form of an image;

designating an image region based on an expected radar return characteristic;

determining a focus operator from the data representative of the image region and a data subspace including a restored form of the image; and

applying the focus operator to the data to generate information representative of the restored form of the image.

2. The method of claim 1, wherein the selected radar return characteristic corresponds to a low radar return relative to a different part of the image.

3. The method of claim 2, wherein the low radar return is approximately zero.

4. The method of claim 2, wherein the image region corresponds to low return image rows.

5. The method of claim 1, which includes applying a sharpness metric.

6. The method of claims 1, wherein the determining of the focus operator includes performing singular value decomposition.

7. A method, comprising:

processing synthetic aperture radar data representative of a defocused image with a processing device;

providing an image processing constraint corresponding to a region of the image expected to have a lower radar return than a different region of the image; and

focusing the defocused image as a function of the image processing constraint and the data.

8. The method of claim 7, which includes generating the synthetic aperture data by oversampling a target.

9. The method of claim 7, wherein the focusing of the defocused image includes performing singular value decomposition.

10. The method of claim 7, wherein the image region has a radar return level of approximately zero.

11. The method of claim 7, which includes performing an adjustment based on a sharpness metric.

12. The method of claim 7, wherein the image region corresponds to a number of image border rows.

13. The method of claim 7, which includes acquiring the synthetic aperture radar data with an aircraft carrying a synthetic aperture radar system.

14. The method of claim 7, which includes characterizing a focused form of the defocused image with a subspace defined by the synthetic aperture radar data.

15. An apparatus, comprising:

a device carrying processor-executable operating logic to process synthetic aperture radar data representative of a defocused image that includes an image processing constraint corresponding to a region of the image expected to have a lower radar return than another region of the image and focusing the defocused image as a function of the processing constraint and a subspace including a focused form of the defocused image.

16. The apparatus of claim 15, further comprising a processor and radar transmission and receiving equipment;

wherein the device is in the form of a memory storing the operating logic executable by the processor.

17. The apparatus of claim 16, further comprising a radar antenna coupled to the equipment and an aircraft carrying the radar antenna and the equipment.

18. The apparatus of claim 15, wherein the device is in the form of at least a portion of a computer network.

19. An apparatus, comprising:

a synthetic aperture radar processing device including;

means for processing synthetic aperture radar data representative of a defocused image;

means for establishing an image processing constraint corresponding to a region of an image expected to have a lower radar return than another region of the image; and

means for focusing the defocused image as a function of the image processing constraint and the data.

20. An apparatus, comprising:

a radar antenna device to acquire synthetic aperture radar data;

radar receiver and transmitter equipment coupled to the radar antenna device; and

a synthetic aperture radar processing device to operatively communicate with the radar receiver and transmitter equipment, the synthetic aperture radar processing device including a processor structured to process the synthetic aperture radar data, the data being representative of a defocused image, the processor being further structured to define an image processing constraint corresponding to a region of the image expected to have a lower radar return than another region of the image and generate one or more output signals as a function of the image processing constraint and the data, the one or more output signals being representative of a more focused form of the defocused image.

21. The apparatus of claim 20, further comprising one or more output devices responsive to the one or more output signals to provide the more focused form of the defocused image.

22. The apparatus of claim 20, further comprising means for moving the antenna and the equipment above ground along a selected track.

23. The apparatus of claim 20, wherein the processor includes means for performing the processing in accordance with a sharpness image metric.

24. The apparatus of claim 20, further comprising an aircraft carrying the antenna device, the equipment, and the synthetic aperture radar processing device.