Phase reference shift for SAR images generated from sub-aperture algorithms

Patent metadata

Field	Value
Publication number	US-9417324-B2
Application number	US-201414180700-A
Country	US
Kind code	B2
Filing date	Feb 14, 2014
Priority date	Feb 14, 2014
Publication date	Aug 16, 2016
Grant date	Aug 16, 2016

Abstract

Embodiments are directed to generating a plurality of sub-images associated with a target via a synthetic aperture radar, processing, by a processor, the sub-images using a sub-aperture algorithm to generate an intermediate image, and applying, by the processor, a phase shift to the intermediate image to generate an output image.

First claim

What is claimed is:

1. A method comprising:
generating a plurality of electronic sub-images associated with a target via a synthetic aperture radar;
processing, by a processor, the sub-images using a sub-aperture algorithm to generate an intermediate image that includes at least one electronic pixel;
applying, by the processor, a phase shift to the intermediate image to generate an output image including at least one phase-shifted pixel; and
displaying the output image including the at least one phase-shifted pixel on an electronic display,
wherein the phase shift corresponds to an exponential of the form:
exp(− j 4π R pixel /λ),

where R pixel corresponds to a distance from a given pixel of a pixel grid to the center of an aperture of the radar, and
λ corresponds to a wavelength of a center band associated with a pulse.

2. The method of claim 1 , wherein the processing of the sub-images comprises summing the sub-images.

3. The method of claim 1 , where the phase shift is applied to the intermediate image on a pixel-by-pixel basis.

4. The method of claim 3 , wherein the phase shift for each pixel is a function of a distance between an aircraft position and the pixel position.

5. The method of claim 1 , further comprising:
applying a coherent change detection algorithm based on the phase shift.

6. The method of claim 1 , further comprising:
applying an autofocus algorithm based on the phase shift.

7. An apparatus comprising:
at least one processor; and
memory having instructions stored thereon that, when executed by the at least one processor, cause the apparatus to:
cause a plurality of electronic sub-images associated with a target to be generated via a synthetic aperture radar;
process the sub-images using a sub-aperture algorithm to generate an intermediate image including at least one pixel;
apply a phase shift to the intermediate image to generate an output image including at least one phase-shifted pixel; and
a display configured to display the electronic output image including the at least one phase-shifted pixel,
wherein the phase shift corresponds to an exponential of the form:
exp(− j 4π R pixel /λ),

where R pixel corresponds to a distance from a given pixel of a pixel grid to the center of an aperture of the radar, and
λ corresponds to a wavelength of a center band associated with a pulse.

8. The apparatus of claim 7 , wherein the instructions, when executed, cause the apparatus to:
process the sub-images by summing the sub-images.

9. The apparatus of claim 7 , wherein the instructions, when executed, cause the apparatus to:
apply the phase shift to the intermediate image on a pixel-by-pixel basis.

10. The apparatus of claim 9 , wherein the phase shift for each pixel is a function of a distance between an aircraft position and the pixel position.

11. The apparatus of claim 7 , wherein the instructions, when executed, cause the apparatus to:
apply a coherent change detection algorithm based on the phase shift.

12. The apparatus of claim 7 , wherein the instructions, when executed, cause the apparatus to:
apply an autofocus algorithm based on the phase shift.

13. An aircraft comprising:
a synthetic aperture radar; and
a computing device configured to:
obtain data corresponding to a plurality of electronic sub-images associated with a target based on pulses emitted via the synthetic aperture radar;
process the sub-images using a sub-aperture algorithm to generate an intermediate image including at least one pixel;
apply a phase shift to the intermediate image to generate an output image including at least one phase-shifted pixel; and
a display configured to display the electronic output image including the at least one phase-shifted pixel,
wherein the phase shift corresponds to an exponential of the form:
exp(− j 4π R pixel /λ),

where R pixel corresponds to a distance from a given pixel of a pixel grid to the center of an aperture of the radar, and
λ corresponds to a wavelength of a center band associated with a pulse emitted by the radar.

14. The aircraft of claim 13 , wherein the computing device is configured to:
process the sub-images by summing the sub-images.

15. The aircraft of claim 13 , wherein the computing device is configured to:
apply the phase shift to the intermediate image on a pixel-by-pixel basis.

16. The aircraft of claim 15 , wherein the phase shift for each pixel is a function of a distance between a position of the aircraft and the pixel position.

17. The aircraft of claim 13 , wherein the computing device is configured to:
apply a coherent change detection algorithm based on the phase shift; and
apply an autofocus algorithm based on the phase shift.

Assignees

• Raytheon Co

Inventors

• Jin Michael Y

Classifications

• G01S13/9035 Primary

  Physics · mapped topic

• G01S13/90

  using synthetic aperture techniques {, e.g. synthetic aperture radar [SAR] techniques} · CPC title

• G01S13/9017

  with time domain processing of the SAR signals in azimuth (G01S13/9005 takes precedence) · CPC title

• G01S13/904 Primary

  SAR modes · CPC title