Apparatus & Method for Short Dwell Inverse Synthetic Aperture Radar (ISAR) Imaging of Turning Moving Vehicles

• US 20130009807A1
• Filed: 07/01/2012
• Published: 01/10/2013
• Est. Priority Date: 07/07/2011
• Status: Active Grant

• Current Assignee: Brian M. Lamb
• Original Assignee: Brian M. Lamb
• Inventors: Lamb, Brian M.
• Granted Patent: US 9,274,219 B2
• Time in Patent Office: Days
• US Class Current: 342/25.B
• CPC Class Codes: G01S 13/5242 with means for platform motion or scan motion compensation, e.g. airborne MTI
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals
• CPC Class Codes: G01S 13/904 SAR modes

Abstract

An apparatus and method for generating a radar image including acquiring a first plurality of data in a first domain, wherein one or more of the first plurality of data include data of a moving target engaged in a turning motion at a rotational rate greater than a threshold; converting the first plurality of data from the first domain to a second plurality of data in a second domain, wherein the second domain is a first two-dimensional transformation of the first domain; extracting one or more of the second plurality of data; converting the one or more of the extracted second plurality of data to a third plurality of data in a third domain, wherein the third domain is a second two-dimensional transformation of the second domain; phase compensating the third plurality of data; and transforming the phase compensated third plurality of data to generate the radar image.

Claims

1. A method for generating a radar image, comprising:

acquiring a first plurality of data in a first domain, wherein one or more of the first plurality of data include data of a moving target engaged in a turning motion at a rotational rate greater than a threshold;

converting the first plurality of data from the first domain to a second plurality of data in a second domain, wherein the second domain is a first two-dimensional transformation of the first domain;

extracting one or more of the second plurality of data;

converting the one or more of the extracted second plurality of data to a third plurality of data in a third domain, wherein the third domain is a second two-dimensional transformation of the second domain;

phase compensating the third plurality of data; and

transforming the phase compensated third plurality of data to generate the radar image.

2. The method of claim 1 further comprising using a cartographic database to determine that the moving target is engaged in the turning motion.

3. The method of claim 1 further comprising measuring Doppler broadening of the moving target.

4. The method of claim 1, wherein the phase compensating step comprises one or more of the following:

applying a parametric polynomial phase correction;

eliminating one or more of range walk, range curvature, or higher order range motion; and

applying phase gradient autofocus.

5. The method of claim 1, further comprising computing an image quality metric of the radar image.

6. The method of claim 1, wherein the transforming step includes performing one or more of the following:

Fourier transformation;

amplitude weighting;

aperture weighting;

apodization;

or Doppler to cross-range transformation.

7. The method of claim 1 further comprising detecting and tracking the moving target to generate tracking data.

8. The method of claim 7, wherein the tracking data is one of the following:

a) used for the extracting one or more of the second plurality of data, b) used for transforming the phase compensated third plurality of data to generate the radar image, or c) used for determining that the moving target is engaged in the turning motion.

9. The method of claim 1, further comprising identifying the radar image as a particular ground vehicle.

10. The method of claim 1, further comprising classifying the radar image into a pre-defined ground vehicle category.

11. The method of claim 7, further comprising using a spatial radar feature of the moving target for tracking.

12. The method of claim 11, wherein the spatial radar feature is one of the following:

length, width, length profile, width profile, or spatial amplitude distribution.

13. The method of claim 1, wherein the threshold is one of the following:

5 degrees per second, 10 degrees per second, or between 1 degree per second and 20 degrees per second.

14. The method of claim 1, wherein the first domain is indexed by fast time and slow time, and the second domain is indexed by range and Doppler.

15. The method of claim 1, wherein the second domain is indexed by range and Doppler.

16. The method of claim 1, wherein a prediction of the turning motion is based on a road network database or an a priori information.

17. The method of claim 1, wherein the third domain includes one of the following:

a fast time dimension with a slow time dimension;

or a fast time dimension with a pose angle dimension.

18. The method of claim 1, further comprising applying adaptive motion compensation to the third plurality of data following the phase compensating step.

19. The method of claim 1, wherein the extracting step includes cropping the second plurality of data to isolate a high value target (HVT) range Doppler blur.

20. The method of claim 1, wherein the phase compensating step includes representing range motion with a low order polynomial.

21. The method of claim 1, wherein the phase compensating step uses a phase gradient autofocus (PGA) algorithm.

22. The method of claim 1, wherein the phase compensating step includes deriving a range rate through a Hough transform.

23. An apparatus for generating a radar image, comprising:

a receiver for acquiring a first plurality of data in a first domain, wherein one or more of the first plurality of data include data of a moving target engaged in a turning motion at a rotational rate greater than a threshold; and

a processor coupled with a memory storing software codes, wherein the software codes are instructions implemented by the processor for;

a) converting the first plurality of data from the first domain to a second plurality of data in a second domain, wherein the second domain is a first two-dimensional transformation of the first domain;

b) extracting one or more of the second plurality of data;

c) converting the one or more of the extracted second plurality of data to a third plurality of data in a third domain, wherein the third domain is a second two-dimensional transformation of the second domain;

d) phase compensating the third plurality of data; and

e) transforming the phase compensated third plurality of data to generate the radar image.

24. The apparatus of claim 23 wherein the processor is further configured for using a cartographic database to determine that the moving target is engaged in the turning motion.

25. The apparatus of claim 23 wherein the processor is further configured for measuring Doppler broadening of the moving target.

26. The apparatus of claim 23, wherein the phase compensating software code further comprises one or more of the following:

software code for applying a parametric polynomial phase correction;

software code for eliminating one or more of range walk, range curvature, or higher order range motion; and

software code for applying phase gradient autofocus.

27. The apparatus of claim 23 wherein the processor is further configured for computing an image quality metric of the radar image.

28. The apparatus of claim 23, wherein the transforming software code further comprises software code for performing one or more of the following:

Fourier transformation;

amplitude weighting;

aperture weighting;

apodization;

or Doppler to cross-range transformation.

29. The apparatus of claim 23 wherein the processor is further configured for detecting and tracking the moving target to generate tracking data.

30. The apparatus of claim 29, wherein the tracking data is one of the following:

a) used for the extracting one or more of the second plurality of data, b) used for transforming the phase compensated third plurality of data to generate the radar image, or c) used for determining that the moving target is engaged in the turning motion.

31. The apparatus of claim 23 wherein the processor is further configured for identifying the radar image as a particular ground vehicle.

32. The apparatus of claim 23 wherein the processor is further configured for classifying the radar image into a pre-defined ground vehicle category.

33. The apparatus of claim 29 wherein the processor is further configured for using a spatial radar feature of the moving target for tracking.

34. The apparatus of claim 33, wherein the spatial radar feature is one of the following:

length, width, length profile, width profile, or spatial amplitude distribution.

35. The apparatus of claim 23, wherein the threshold is one of the following:

degrees per second, 10 degrees per second, or between 1 degree per second and 20 degrees per second.

36. The apparatus of claim 23, wherein the first domain is indexed by fast time and slow time, and the second domain is indexed by range and Doppler.

37. The apparatus of claim 23, wherein the second domain is indexed by range and Doppler.

38. The apparatus of claim 23, wherein a prediction of the turning motion is based on a road network database or an a priori information.

39. The apparatus of claim 23, wherein the third domain includes one of the following:

a fast time dimension with a slow time dimension;

or a fast time dimension with a pose angle dimension.

40. The apparatus of claim 23 wherein the processor is further configured for applying adaptive motion compensation to the third plurality of data following the phase compensating step.

41. The apparatus of claim 23, wherein the extracting software code further comprises software code for cropping the second plurality of data to isolate a high value target (HVT) range Doppler blur.

42. The apparatus of claim 23, wherein the phase compensating software code further comprises software code for representing range motion with a low order polynomial.

43. The apparatus of claim 23, wherein the phase compensating software code further comprises software code for using a phase gradient autofocus (PGA) algorithm.

44. The apparatus of claim 23, wherein the phase compensating software code further comprises software code for deriving a range rate through a Hough transform.