US5898399A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Subchirp processing method
Assignee: MDA Information Systems Inc
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Filing: 1996-05-10
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Granted: 1999-04-27
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Expires: 2016-05-10
Abstract
Abstract A method of performing the computer-intensive initial steps of the range migration algorithm, or RMA, produces radar imagery of higher quality than the current polar format (PF) processing approach, while operating faster and more efficiently than the standard RMA. The new method is advantageous when the synthetic aperture length required to achieve azimuth resolution is significantly larger than the azimuth extent of the processed scene. The method subdivides the signal history into a plurality of non-overlapping subapertures, adds a low bandwidth azimuth chirp across each subaperture and applies a fast Fourier transform separately to each subaperture. The results are coherently combined, after which the remaining steps of the conventional RMA may be completed with minor modifications to the subsequent two-dimensional phase compensation. The invention is applicable to spotlight, stripmap and scan-mode SAR image formation, and the separate, subaperture Fourier transformations may be performed simultaneously.
Inventors
- 👤 Walter G. Carrara
- 👤 Ron S. Goodman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 08:58
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/88; G01S13/89; G01S13/90; G01S13/904; G01S13/9054; G01S13/9056
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
96 words
The method of forming a synthetic aperture radar (SAR) image, comprising the steps of: receiving SAR signal history data; motion compensating the signal history data to a fixed scene point; subdividing the signal history data into a plurality of non-overlapping subapertures; adding a low-bandwidth chirp in azimuth to each subaperture; Fourier transforming each subaperture separately; shifting and coherently summing the results of the separate Fourier transformations to yield full-bandwidth transform data; resampling the full-bandwidth transform data in the range dimension; and performing a two-dimensional inverse Fourier transformation on the resampled data to generate a complex image.
Claim 2
Independent Claim
96 words
The method of forming a synthetic aperture radar (SAR) image, comprising the steps of: receiving SAR signal history data; motion compensating the signal history data to a fixed scene point; subdividing the signal history data into a plurality of non-overlapping subapertures; adding a low-bandwidth chirp in azimuth to each subaperture; Fourier transforming each subaperture separately; shifting and coherently summing the results of the separate Fourier transformations to yield full-bandwidth transform data; resampling the full-bandwidth transform data in the range dimension; and performing a two-dimensional inverse Fourier transformation on the resampled data to generate a complex image.
Claim 3
Dependent Claim
16 words
The method of claim 1, wherein the steps are performed to generate a spotlight-type SAR image.
Claim 4
Dependent Claim
16 words
The method of claim 1, wherein the steps are performed to generate a stripmap-type SAR image.
Claim 5
Dependent Claim
16 words
The method of claim 1, wherein the steps are performed to generate a scan-mode SAR image.
Claim 6
Dependent Claim
12 words
The method of claim 1, including the use of fast Fourier transformations.
Claim 7
Dependent Claim
14 words
The method of claim 1, wherein the separate subaperture Fourier transformations are performed simultaneously.
Claim 8
Dependent Claim
67 words
In a SAR image processing system utilizing a range migration algorithm (RMA), the method of performing the azimuth FFT of the RMA, comprising the steps of: receiving an azimuth-chirped signal history; subdividing the signal history into a plurality of non-overlapping subapertures; adding a low-bandwidth chirp in azimuth to each subaperture; applying an FFT to each subaperture; coherently adding the results of the FFTs; and completing the RMA.
Claim 9
Dependent Claim
67 words
In a SAR image processing system utilizing a range migration algorithm (RMA), the method of performing the azimuth FFT of the RMA, comprising the steps of: receiving an azimuth-chirped signal history; subdividing the signal history into a plurality of non-overlapping subapertures; adding a low-bandwidth chirp in azimuth to each subaperture; applying an FFT to each subaperture; coherently adding the results of the FFTs; and completing the RMA.
Claim 10
Dependent Claim
16 words
The method of claim 7, wherein the steps are performed to generate a spotlight-type SAR image.
Claim 11
Dependent Claim
16 words
The method of claim 7, wherein the steps are performed to generate a stripmap-type SAR image.
Claim 12
Dependent Claim
16 words
The method of claim 7, wherein the steps are performed to generate a scan-mode SAR image.
Claim 13
Dependent Claim
14 words
The method of claim 7, wherein the separate subaperture Fourier transformations are performed simultaneously.
Claim 14
Dependent Claim
69 words
In a range migration algorithm (RMA) of the type used to generate SAR imagery, the improvement comprising the replacement of the first along-track FFT of the RMA with the following steps: subdividing the signal history into a plurality of non-overlapping subapertures; adding a low-bandwidth chirp in azimuth to each subaperture; applying an FFT to each subaperture; and coherently adding the results of the FFTs to obtain full transform data.
Claim 15
Dependent Claim
69 words
In a range migration algorithm (RMA) of the type used to generate SAR imagery, the improvement comprising the replacement of the first along-track FFT of the RMA with the following steps: subdividing the signal history into a plurality of non-overlapping subapertures; adding a low-bandwidth chirp in azimuth to each subaperture; applying an FFT to each subaperture; and coherently adding the results of the FFTs to obtain full transform data.
References Cited (Backward Citations)
US4134113A
Cited
US5191344A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2002-04-26 | 2002-10-26 | 2003-04-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2006-04-26 | 2006-10-26 | 2007-04-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2010-04-26 | 2010-10-26 | 2011-04-27 | $7700.00 | Window Closed / Lapsed |