Backprojection Subimage Autofocus of Moving Ships for Synthetic Aperture Radar

We propose a new autofocus approach for the backprojection reconstruction algorithm to compute high-quality synthetic aperture radar images of non-linearly moving and maneuvering ships. In contrast to the state-of-the-art autofocus techniques, our approach allows a long coherent processing interval...

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Bibliographic Details
Published in:IEEE transactions on geoscience and remote sensing 2019-11, Vol.57 (11), p.8383-8393
Main Authors: Sommer, Aron, Ostermann, Jorn
Format: Article
Language:English
Subjects:
Airborne radar
Airborne remote sensing
Algorithms
Antennas
Classification
Image classification
Image contrast
Image contrast autofocus
image entropy
Image quality
Image reconstruction
inverse problems
inverse synthetic aperture radar (ISAR)
Levenberg–Marquardt
maneuvering objects
Marine vehicles
Phase error
Radar
Radar imaging
regularization
SAR (radar)
Sharpness
ship autofocus
Ships
Spaceborne radar
Superhigh frequencies
Synthetic aperture radar
synthetic aperture radar (SAR)
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Summary:We propose a new autofocus approach for the backprojection reconstruction algorithm to compute high-quality synthetic aperture radar images of non-linearly moving and maneuvering ships. In contrast to the state-of-the-art autofocus techniques, our approach allows a long coherent processing interval even in the case of a rough sea, which improves the image quality. An improved image quality enables the classification of ships in airborne synthetic aperture radar (SAR) images. For this purpose, we decompose the image into subimages and estimate pulse-by-pulse a phase error for each subimage by maximizing subimage sharpness. A regularized Levenberg-Marquardt algorithm guarantees a smooth phase correction on subimage level. By correcting the subsequent range distances from the flight path to all pixels using the currently estimated phase errors, sharp images of maneuvering ships with arbitrary velocities can now be reconstructed. The evaluation of our proposed ship autofocus technique on the basis of real airborne X-band data shows that our approach leads to a visible improvement of image quality in comparison with the state-of-the-art techniques. Given these results, even an automatic ship classification based on radar images might be possible in the future.
ISSN:0196-2892
1558-0644
DOI:10.1109/TGRS.2019.2920779