Coherent and semi-coherent processing of limited-aperture circular synthetic aperture (CSAS) data

Marston, Timothy M.; Kennedy, Jermaine L.; Marston, Philip L.

doi:10.23919/oceans.2011.6107280

Cited by 18 publications

(14 citation statements)

References 9 publications

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“…• Circular SAS [12] could be ideally suited as well for increasing the angular coverage. This requires circling around the object in order to obtain information from all angles.…”

Section: 32mentioning

confidence: 99%

UXO Detector for Underwater Surveys Using Low-Frequency Sonar

Vossen¹,

Hunter²,

Duijster³

et al. 2015

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“…• Circular SAS [12] could be ideally suited as well for increasing the angular coverage. This requires circling around the object in order to obtain information from all angles.…”

Section: 32mentioning

confidence: 99%

UXO Detector for Underwater Surveys Using Low-Frequency Sonar

Vossen¹,

Hunter²,

Duijster³

et al. 2015

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“…(21), U n is the Fourier spectral representation of the defocused image and M n is a tapered mask that attenuates spectral information outside aspects ranging from w nÀdw to w nþdw and is used to generate sub-aperture images. 12 The square-root term in Eq. (22) equals the radial spatial wavenumber k, and for implementation purposes is formed by taking the Euclidean sum of the k x and k y values corresponding to each sample of the two-dimensional scene spectrum.…”

Section: Component Cone Estimationmentioning

confidence: 99%

“…12 The aperture was divided into 180 segments, each having a total width of 20 . Contrast maximization for each segment was conducted by using successive parabolic interpolations over the range of sampled curvature values bounding the peak contrast measurement.…”

Section: Verification and Applicationmentioning

confidence: 99%

Autofocusing circular synthetic aperture sonar imagery using phase corrections modeled as generalized cones

Marston

Kennedy

Marston

2014

The Journal of the Acoustical Society of America

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Circular synthetic aperture sonar (CSAS) is a coherent aperture synthesis technique that utilizes backscattered acoustic information from an encircled scene to generate information rich, high-resolution imagery. The aperture length required for image synthesis is much longer than in its linear synthetic aperture sonar counterpart and can result in challenging phase delay and navigation estimation constraints. Residual uncorrected phase errors manifest as focus aberrations in reconstructed CSAS imagery. This paper demonstrates that phase error in image patches can be approximated as an aspect variant linear phase shift representable as a generalized cone in wave-number space. If the geometry of the generalized cone is known, it can be applied as the spectral phase of an inverse filter for aberration correction. A method is derived for reconstructing the error cone geometry from independent estimates of its local curvatures, which are found via a series of one-dimensional line searches that maximize the focus of CSAS sub-aperture images. This approach is applied to real and simulated CSAS data containing aperture distortions, and the results successfully demonstrate estimation and correction of the underlying focus aberrations.

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“…This is the exact same problem that sidescan sonar makes, and sidescan systems have inherently lower maximum resolutions versus synthetic aperture based systems. 4,5 Therefore, the synthetic aperture focusing technique (SAFT) method is also introduced to enhance the spatial resolution of images in UNDT.…”

Section: Introductionmentioning

confidence: 99%

Frequency domain synthetic aperture focusing technique for variable-diameter cylindrical components

Jin

et al. 2017

The Journal of the Acoustical Society of America

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Ultrasonic non-destructive testing (UNDT) plays an important role in ensuring the quality of cylindrical components of equipment such as pipes and axles. As the acoustic beam width widens along propagation depths, the diffraction of acoustic wave becomes serious and the images of defects will be interfered with. To precisely evaluate the dimensions of defects and flaws concealed in components, the synthetic aperture focusing technique (SAFT) is introduced to enhance the image resolutions. Conventional SAFTs have been successfully implemented for the ultrasonic imaging of normal cylinders, while solutions for complex ones, such as variable-diameter cylinders, are still lacking. To overcome this problem, a frequency-domain SAFT for variable-diameter cylindrical components is proposed. This algorithm is mainly based on acoustic field extrapolation, which is modified from cylindrical phase shift migration with the aid of split-step Fourier. After a series of extrapolations, a high-resolution ultrasound image can be reconstructed using a particular imaging condition. According to the experimental results, the proposed method yields low side lobes and high resolutions for flat transducers. Its attainable angular resolution relies on the transducer diameter D and scanning radius R and approximates D/(2R).

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Coherent and semi-coherent processing of limited-aperture circular synthetic aperture (CSAS) data

Cited by 18 publications

References 9 publications

UXO Detector for Underwater Surveys Using Low-Frequency Sonar

UXO Detector for Underwater Surveys Using Low-Frequency Sonar

Autofocusing circular synthetic aperture sonar imagery using phase corrections modeled as generalized cones

Frequency domain synthetic aperture focusing technique for variable-diameter cylindrical components

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