Flight path-driven mitigation of wavefront curvature effects in SAR images

• US 7,551,119 B1
• Filed: 01/08/2008
• Issued: 06/23/2009
• Est. Priority Date: 01/08/2008
• Status: Active Grant

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Doerry, Armin W.
• Primary Examiner(s): Sotomayor; John B
• Application Number:
  US11/970,631
• Time in Patent Office: 532 Days
• Field of Search: 342/25.R, 342 25 A- 25 F, 342/159, 342/162, 342/194, 342/195
• US Class Current: 342/25.00R
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals
• CPC Class Codes: G01S 13/904 SAR modes

Abstract

A wavefront curvature effect associated with a complex image produced by a synthetic aperture radar (SAR) can be mitigated based on which of a plurality of possible flight paths is taken by the SAR when capturing the image. The mitigation can be performed differently for different ones of the flight paths.

Claims

1. A synthetic aperture radar (SAR) apparatus, comprising:

an input for receiving a complex image associated with a SAR reflection signal reflected by a target in response to a SAR transmit signal transmitted from an airborne platform that is capable of executing any one of a plurality of different flight paths during transmission of said SAR transmit signal; and

a mitigation unit coupled to said input for mitigating a SAR wavefront curvature effect associated with said complex image based on which of said flight paths is executed by the airborne platform during transmission of said SAR transmit signal, said mitigation unit operable to perform said mitigating differently for different ones of said flight paths.

2. The apparatus of claim 1, wherein said mitigation unit is configured to apply to said complex image any of a plurality of different mitigation operations that respectively correspond to said plurality of different flight paths, and wherein said mitigation unit is operable for applying to said complex image the one of said mitigation operations that corresponds to the flight path executed by the airborne platform during transmission of said SAR transmit signal.

3. The apparatus of claim 2, wherein said one mitigation operation mitigates a defocusing effect associated with said complex image.

4. The apparatus of claim 3, wherein said one mitigation operation mitigates a geometric distortion effect associated with said complex image.

5. The apparatus of claim 2, wherein said one mitigation operation mitigates a geometric distortion effect associated with said complex image.

6. The apparatus of claim 5, wherein said geometric distortion effect includes a range distortion effect.

7. The apparatus of claim 5, wherein said geometric distortion effect includes an azimuth distortion effect.

8. The apparatus of claim 7, wherein said geometric distortion effect includes a range distortion effect.

9. The apparatus of claim 2, wherein said one mitigation operation includes a deconvolution operation.

10. The apparatus of claim 9, wherein said deconvolution operation deconvolves said complex image with a signal representation of a phase error associated with the SAR reflection signal when the flight platform executes said one flight path during transmission of said SAR transmit signal.

11. The apparatus of claim 2, wherein said mitigation unit includes an image divider for dividing said complex image into a plurality of sub-images, and applies said one mitigation operation separately to each of said sub-images.

12. A synthetic aperture radar (SAR) method, comprising:

providing a complex image associated with a SAR reflection signal reflected by a target in response to a SAR transmit signal transmitted from an airborne platform that is capable of executing any one of a plurality of different flight paths during transmission of said SAR transmit signal; and

mitigating a SAR wavefront curvature effect associated with said complex image based on which of said flight paths is executed by the airborne platform during transmission of said SAR transmit signal, including performing said mitigating differently for different ones of said flight paths.

13. The method of claim 12, wherein said mitigating further includes providing a plurality of different mitigation operations that respectively correspond to said plurality of different flight paths, and applying to said complex image the one of said mitigation operations that corresponds to the flight path executed by the airborne platform during transmission of said SAR transmit signal.

14. The method of claim 13, wherein said one mitigation operation mitigates a defocusing effect associated with said complex image.

15. The method of claim 14, wherein said one mitigation operation mitigates a geometric distortion effect associated with said complex image.

16. The method of claim 13, wherein said one mitigation operation mitigates a geometric distortion effect associated with said complex image.

17. The method of claim 13, wherein said one mitigation operation includes a deconvolution operation.

18. The method of claim 17, wherein said deconvolution operation deconvolves said complex image with a signal representation of a phase error associated with the SAR reflection signal when the flight platform executes said one flight path during transmission of said SAR transmit signal.

19. The method of claim 13, wherein said mitigating further includes dividing said complex image into a plurality of sub-images, and applying said one mitigation operation separately to each of said sub-images.

20. A SAR apparatus, comprising:

a SAR unit for transmitting a SAR transmit signal while carried aboard an airborne platform that is capable of executing any one of a plurality of different flight paths during transmission of said SAR transmit signal, said SAR unit having an input for receiving a SAR reflection signal reflected by a target in response to said SAR transmit signal;

an image formation unit coupled to said SAR unit for producing a complex image based on said SAR reflection signal; and

a mitigation unit coupled to said image formation unit for mitigating a SAR wavefront curvature effect associated with said complex image based on which of said flight paths is executed by the airborne platform during transmission of said SAR transmit signal, said mitigation unit operable to perform said mitigating differently for different ones of said flight paths.

21. The apparatus of claim 20, wherein said mitigation unit is configured to apply to said complex image any of a plurality of different mitigation operations that respectively correspond to said plurality of different flight paths, and wherein said mitigation unit is operable for applying to said complex image the one of said mitigation operations that corresponds to the flight path executed by the airborne platform during transmission of said SAR transmit signal.

22. The apparatus of claim 21, wherein said one mitigation operation mitigates a defocusing effect associated with said complex image.

23. The apparatus of claim 22, wherein said one mitigation operation mitigates a geometric distortion effect associated with said complex image.

24. The apparatus of claim 21, wherein said one mitigation operation mitigates a geometric distortion effect associated with said complex image.