Strip-Map SAR Auto-Focus Phase Error Estimation
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Solution Overview
Problem
Conventional strip-map SAR auto-focus image generation techniques face challenges in accurately concatenating batch images and managing phase errors, leading to residual phase errors and decreased image quality due to limitations in estimating constant and linear phase offsets and high-order phase variations.
Innovation Solution
The method involves estimating the first derivative of phase errors at the edges of batch images to compensate for chronological shifts during auto-focus processing, allowing for improved abutment and selection of raw radar return data, and applying phase corrections to ensure accurate image alignment and quality management by rejecting auto-focused images that do not meet predetermined criteria.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional auto-focus techniques are used to correct phase errors, then quadratic phase variations are corrected, but constant and linear phase offsets remain uncorrected
Solution Approach 1:
The patent segments the phase error correction process into multiple components: constant phase offset correction, linear phase gradient correction, and quadratic phase curvature correction. Each component is handled separately through specific processing steps, allowing comprehensive correction of all phase error types that were previously addressed as a single quadratic term.
Solution Approach 2:
The patent changes the parameters being corrected by extending the correction model from only quadratic phase terms to include constant and linear phase terms. This is achieved by modifying the phase correction algorithm to estimate and correct multiple phase error components simultaneously, thereby improving overall phase correction accuracy.
2Productivity
If batch processing is used to handle large images, then processing efficiency is improved, but discontinuities and misalignment occur at batch boundaries
Solution Approach 1:
The patent applies preliminary phase correction and alignment processing to batch images before final abutment. By pre-correcting phase errors and estimating chronological shifts at batch boundaries, the system ensures that images can be efficiently processed in batches while maintaining accurate alignment when concatenated, thus resolving the boundary discontinuity problem.
3Productivity
If matched filter processing is used for efficient batch processing, then processing speed is improved, but invalid regions are created requiring data discarding
Solution Approach 1:
The patent applies local quality adjustment by differentiating processing approaches for different regions of batch images. Valid regions are processed with standard matched filter efficiency, while boundary regions are subjected to additional phase correction and alignment processing. This localized approach maintains overall processing efficiency while ensuring accurate abutment without excessive data discarding.
Data Source
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AI summary
A strip-map Synthetic Aperture Radar (SAR) auto-focus image generation process is provided. Batches of raw radar return data are processed in order to form batch images which each have a valid region between invalid regions. The process determines an estimate of the first derivative of a phase error at an end of the valid region, determines a time-shift corresponding to that estimate and uses that information in determining a starting point for the next batch of raw radar return data.