Methods for two-dimensional autofocus in high resolution radar systems

• US 20100149024A1
• Filed: 02/12/2010
• Published: 06/17/2010
• Est. Priority Date: 08/15/2006
• Status: Active Grant

• Current Assignee: Maxar Mission Solutions Incorporated (Galileo Parent, Inc.)
• Original Assignee: General Dynamics Advanced Information Systems Incorporated (General Dynamics Corporation)
• Inventors: Goodman, Rod S., Batteh, Elizabeth T., Gabl, Edward F., Ricoy, Mark A., Connell, Scott D.
• Granted Patent: US 7,843,377 B2
• Time in Patent Office: Days
• US Class Current: 342/25.F
• CPC Class Codes: G01S 13/9011 with frequency domain processing of the SAR signals in azimuth G01S13/9005 takes precedence
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals

Abstract

Provided are two-dimensional autofocus methods in a synthetic aperture radar (SAR) system which include: (1) two-dimensional pulse pair product algorithm including shear PGA, eigenvector phase history (“EPH”), shear PGA/EPH); (2) two-dimensional optimization algorithms including parametric one-dimensional estimate/two-dimensional correction, parametric two dimensional estimate/two-dimensional correction, unconstrained two-dimensional nonparametric and constrained two-dimensional nonparametric methods; (3) a two-dimensional geometry filter algorithm; (4) a two-dimensional prominent point processing algorithm; (5) a one-dimensional phase estimate of higher order two dimensional phase errors; and, (6) a fast SHARP parametric autofocus algorithm.

Claims

1-48. -48. (canceled)

49. A two-dimensional polar geometry model method used in a synthetic aperture radar (SAR) system for removing a two-dimensional phase error in a complex image, the method comprising:

creating the complex image with a sensor;

modeling the two-dimensional phase error as a combination of a range error which is substantially identical from pulse to pulse and a slow-time error;

fitting an unconstrained two-dimensional estimate to the modeled two-dimensional phase error; and

correcting the two-dimensional phase error to generate a corrected image.

50. The method according to claim 49, wherein the modeling the two-dimensional phase error is solely based on azimuth or range.

51. The method according to claim 49, wherein the modeled two-dimensional phase error is represented as two one-dimensional vectors or two sets of parametric basic vectors.

52. The method according to claim 51, wherein a contrast metric is used to determine whether to use a model fit of original data which maximizes the contrast metric.

53. The method according to claim 52, wherein the contrast metric utilizes a line-power normalization of the complex image, a column-power normalization, or both.

55. The computer-readable medium according to claim 51, wherein the modeling the two-dimensional phase error is solely based on azimuth or range.

54. A computer-readable medium having computer-executable instructions for a two-dimensional polar geometry filter method used in a synthetic aperture radar (SAR) system for removing a two-dimensional phase error in a complex image, the computer-executable instructions configured to perform a method comprising:

creating the complex image with a sensor;

modeling the two-dimensional phase error as a combination of a range error which is substantially identical from pulse to pulse and a slow-time error;

fitting an unconstrained two-dimensional estimate to the modeled two-dimensional phase error; and

correcting the two-dimensional phase error to generate a corrected image.

56. The computer-readable medium according to claim 54, wherein the modeled two-dimensional phase error is represented as two one-dimensional vectors or two sets of parametric basic vectors.

57. The method according to claim 56, wherein a contrast metric is used to determine whether to use a model fit of the original data based on which maximizes the contrast metric.

58. The method according to claim 57, wherein the contrast metric utilizes a line-power normalization of the complex image, a column-power normalization, or both.

59-149. -149. (canceled)