Phase gradient auto-focus for SAR images
First Claim
1. A method of processing an uncorrected azimuth line vector selected from an unfocused array into a corrected azimuth line vector comprising steps of:
- forming a bright spot list based on the selected uncorrected azimuth line vector, the bright spot list including at least one bright spot entry;
unpacking the uncorrected azimuth line vector into an uncorrected segment set, the uncorrected segment set including a first uncorrected segment corresponding to a first bright spot entry in the bright spot list;
processing the first uncorrected segment into a first corrected segment based on an average phase slope corresponding to the first bright spot entry; and
packing the first corrected segment into the corrected azimuth line vector.
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Abstract
A SAR image auto-focus method uses statistics extracted from the image data to develop a phase pure hyperbolic correction function. The method processes an uncorrected azimuth line vector selected from an unfocused array into a corrected azimuth line vector. The method includes forming a bright spot list based on the selected uncorrected azimuth line vector where the bright spot list has at least one bright spot entry. Then, the uncorrected azimuth line vector is unpacked into an uncorrected segment set that has a first uncorrected segment corresponding to a first bright spot entry in the bright spot list. Then, the first uncorrected segment is processed into a first corrected segment based on an average phase slope corresponding to the first bright spot entry, the first corrected segment is packed into the corrected azimuth line vector, and the process repeated for all bright spots. The step of processing the first uncorrected segment into a first corrected segment includes processing the first uncorrected segment through a Fourier transform into an uncorrected spectrum vector, correcting the uncorrected spectrum vector to form a corrected spectrum vector, processing the corrected spectrum vector through an inverse Fourier transform into the first corrected segment. The step of correcting the uncorrected spectrum vector includes computing phase gradient φdot (f) at each frequency f in the uncorrected spectrum vector based on:
φ.sub.dot (f)=Im {G(f).sup.•
G'"'"'(f)}/(2π|G(f)|2),
then computing the average phase slope by averaging the phase gradient determined at each frequency in the uncorrected spectrum vector. Then a correction function vector corresponding to the average phase slope is generated, and the uncorrected spectrum vector is multiplied by the correction function vector, element by element, to form the corrected spectrum vector.
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Citations
33 Claims
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1. A method of processing an uncorrected azimuth line vector selected from an unfocused array into a corrected azimuth line vector comprising steps of:
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forming a bright spot list based on the selected uncorrected azimuth line vector, the bright spot list including at least one bright spot entry; unpacking the uncorrected azimuth line vector into an uncorrected segment set, the uncorrected segment set including a first uncorrected segment corresponding to a first bright spot entry in the bright spot list; processing the first uncorrected segment into a first corrected segment based on an average phase slope corresponding to the first bright spot entry; and packing the first corrected segment into the corrected azimuth line vector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A computing machine comprising:
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a processor; a first module to form a bright spot list based on an uncorrected azimuth line vector selected from an unfocused array, the bright spot list including at least one bright spot entry; a second module to unpack the uncorrected azimuth line vector into an uncorrected segment set, the uncorrected segment set including a first uncorrected segment corresponding to a first bright spot entry in the bright spot list; a third module to process the first uncorrected segment into a first corrected segment based on an average phase slope corresponding to the first bright spot entry; and a fourth module to pack the first corrected segment into a corrected azimuth line vector. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A computer readable medium having stored thereon a plurality of modules for controlling a processor, the plurality of modules comprising:
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a first module to control the processor to form a bright spot list based on an uncorrected azimuth line vector selected from an unfocused array, the bright spot list including at least one bright spot entry; a second module to control the processor to unpack the uncorrected azimuth line vector into an uncorrected segment set, the uncorrected segment set including a first uncorrected segment corresponding to a first bright spot entry in the bright spot list; a third module to control the processor to process the first uncorrected segment into a first corrected segment based on an average phase slope corresponding to the first bright spot entry; and a fourth module to control the processor to pack the first corrected segment into a corrected azimuth line vector. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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Specification