US5854602A
Expired / Lapsed
US
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Subaperture high-order autofocus using reverse phase
Assignee: MDA Information Systems Inc
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Filing: 1997-04-28
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Granted: 1998-12-29
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Expires: 2017-04-28
Abstract
Abstract A high-order synthetic aperture radar (SAR) autofocusing method decomposes phase error into basis function components, one order at a time. Image patches are partitioned into a plurality of subapertures in accordance with positive- and negative-going slope of the basis function at each order. A positive mask is applied to each subaperture within which the basis function is increasing in slope, whereas a negative mask is applied to each subaperture within which the basis function is decreasing in slope. The results are then correlated to obtain a focused image, with the principle of map-drift preferably being used to compute phase-amplitude weights. The method may be uniformly applied, enabling the steps to be performed at a plurality of increasingly higher orders without performance degradation.
Inventors
- 👤 Herbert C. Stankwitz
- 👤 Ken W. Burgener
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 16:00
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/88; G01S13/89; G01S13/90; G01S13/904; G01S13/9004; G01S13/9019
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
108 words
A method of autofocusing a synthetic radar (SAR) image, comprising the steps of: (a) receiving a complex, unfocused SAR image comprised of a plurality of image patches; (b) partitioning the Fourier transform of each patch into a plurality of subapertures, each partition being associated with the maxima and minima of a basis function for the current order; (c) applying a positive mask to each subaperture wherein the basis function is increasing in phase slope, and applying a negative mask to each subaperture wherein the basis function is decreasing in phase slope; and (d) correlating the results of the masking, operations of step (c) to obtain a focused image.
Claim 2
Independent Claim
108 words
A method of autofocusing a synthetic radar (SAR) image, comprising the steps of: (a) receiving a complex, unfocused SAR image comprised of a plurality of image patches; (b) partitioning the Fourier transform of each patch into a plurality of subapertures, each partition being associated with the maxima and minima of a basis function for the current order; (c) applying a positive mask to each subaperture wherein the basis function is increasing in phase slope, and applying a negative mask to each subaperture wherein the basis function is decreasing in phase slope; and (d) correlating the results of the masking, operations of step (c) to obtain a focused image.
Claim 3
Dependent Claim
14 words
The method of claim 1, wherein the basis function is a Fourier basis function.
Claim 4
Dependent Claim
14 words
The method of claim 1, wherein the basis function is a Legendre basis function.
Claim 5
Dependent Claim
21 words
The method of claim 1, wherein steps (b) and (c) are repeated for each of a plurality of increasingly higher orders.
Claim 6
Dependent Claim
14 words
The method of claim 1, wherein the step of correlating is based on map-drift.
Claim 7
Independent Claim
84 words
A method of autofocusing a synthetic aperture radar (SAR) image, comprising the steps of: receiving a complex, unfocused SAR image comprised of a plurality of image patches; processing each patch at a plurality of orders wherein, at each order, the patch is divided into a plurality of subapertures according to the change in basis function slope for that order, and masked as a function of positive-going and negative-going basis function slope; and correlating the results of the previous step to obtain a focused image.
Claim 8
Independent Claim
84 words
A method of autofocusing a synthetic aperture radar (SAR) image, comprising the steps of: receiving a complex, unfocused SAR image comprised of a plurality of image patches; processing each patch at a plurality of orders wherein, at each order, the patch is divided into a plurality of subapertures according to the change in basis function slope for that order, and masked as a function of positive-going and negative-going basis function slope; and correlating the results of the previous step to obtain a focused image.
Claim 9
Dependent Claim
14 words
The method of claim 6, wherein the basis function is a Legendre basis function.
Claim 10
Dependent Claim
14 words
The method of claim 6, wherein the basis function is a Fourier basis function.
Claim 11
Dependent Claim
140 words
The method of claim 8, wherein the step of processing each patch further includes the steps of: receiving a complex image patch; performing an inverse Fourier transformation on the image patch to generate a range-compressed image patch in the signal domain; applying any lower-order phase corrections to the range-compressed image patch, if such corrections were previously carried out; partitioning the patch into a plurality of subapertures, each partition being associated with the maxima and minima of the Fourier basis function for the current order; applying a positive mask to each subaperture if the slope of the Fourier basis function is increasing within that aperture, and applying a negative mask to each subaperture if the slope of the Fourier basis function is decreasing within that aperture; and performing a Fourier transformation and magnitude detection on the positively and negatively masked subapertures.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2001-12-28 | 2002-06-29 | 2002-12-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2005-12-28 | 2006-06-29 | 2006-12-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2009-12-28 | 2010-06-29 | 2010-12-29 | $7700.00 | Window Closed / Lapsed |