SAR Image Autofocus via Segmented Illumination
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Solution Overview
Problem
Current SAR image construction methods face challenges in achieving high-resolution images due to inaccuracies in measuring the radar antenna's phase center trajectory, leading to defocusing issues, and they do not allow for real-time image generation or optimization of radar signal processing without complete illumination.
Innovation Solution
A method that divides the radar illumination period into overlapping sub-periods, applies autofocus processing to each sub-period image, and iteratively combines these images to achieve the desired resolution, incorporating both coherent and non-coherent combination techniques to refine and enhance image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the illumination time is extended to achieve fine resolution, then the transverse resolution is improved, but the trajectory measurement errors increase causing deterioration in focusing quality
Solution Approach 1:
The patent divides the complete illumination period into multiple sub-periods, each shorter than the full illumination time. For each sub-period, a separate image is formed with corresponding trajectory measurements. This segmentation allows each image to be formed with acceptable trajectory precision while the combination of multiple images achieves the fine resolution of the complete illumination period.
Solution Approach 2:
The patent applies autofocus processing to each sub-period image to correct focusing defects caused by trajectory measurement errors. This feedback mechanism estimates and compensates for residual defocusing, improving the quality of each individual image before combination, thereby mitigating the impact of trajectory measurement inaccuracies.
2Manufacturing precision
If the complete illumination period is waited for full resolution image formation, then the image resolution is maximized, but the processing time is increased and real-time capability is lost
Solution Approach 1:
The patent segments the illumination period into overlapping sub-periods that can be processed independently and in parallel. This allows image formation to begin before the complete illumination period ends, reducing processing time while maintaining the ability to achieve fine resolution through combination of multiple sub-period images.
Solution Approach 2:
The patent performs autofocus processing and image combination operations on sub-period images during the ongoing illumination process rather than waiting for completion. This preliminary action enables real-time or near-real-time image generation, reducing the loss of time while preserving resolution quality.
3Reliability
If multiple images are combined to reduce radiometric noise, then the noise level is decreased, but the processing complexity increases
Solution Approach 1:
The patent organizes the combination process by dividing images into sets based on temporal succession and resolution levels. This structured segmentation of the combination process manages complexity by handling images in organized groups rather than all-at-once, while still achieving noise reduction through multiple combinations.
Data Source
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AI summary
The present invention relates to a method for constructing focused radar images, the method comprising at least the following steps: ■ dividing the radar illumination period into p sub-periods, with any two successive sub-periods overlapping temporally (201); ■ selecting n successive sub-periods from the p sub-periods, and for each of the n selected sub-periods, performing radar acquisitions to generate an IM_0x image with R0 resolution (202); ■ applying autofocus processing to each of the n generated IM_0x images (203); ■ combining the n images (204) to generate at least one new focused radar image IM_1x. The invention is particularly applicable to the production of high-resolution SAR images from an aircraft equipped with a radar antenna.