Hayden J. Callow

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This thesis contains a description of SAS processing algorithms, offering improvements in Fourier-based reconstruction, motion-compensation, and autofocus. Fourier-based image reconstruction is reviewed and improvements shown as the result of improved system modelling. A number of new algorithms based on the wavenumber algorithm for correcting second order(More)
This paper describes the implementation of a bathymetric synthetic aperture sonar and presents preliminary results from sea trials of the sonar. The sonar is designed for high resolution seafloor imaging in a shallow water environment. This is achieved through coherent summation of successive echo signals to synthesise an aperture many times longer than the(More)
Abstract— A significant problem with Synthetic Aperture Sonar (SAS) imaging is the compensation of compensating for unknown errors in the sonar path trajectory. Unknown path errors in SAS have the effect of blurring and smearing the sea-floor image. Inertial navigation systems as used in Synthetic Aperture Radar (SAR), are not accurate enough for use in(More)
− A significant problem in Synthetic Aperture Sonar (SAS) imaging is compensating for unknown errors in the sonar path trajectory. Unknown deviations from the ideal sonar trajectory have the effect of blurring and smearing the sea-floor image. In typical operating conditions, the blurring can completely obscure details in the imaged scene. Techniques for(More)
To boost the mapping rate of synthetic aperture sonars (SASs), systems employing multiple hydrophones are used. Images from these multiple-receiver SAS systems are reconstructed from the recorded data using the same algorithms as in single-receiver SAS. Currently the data-sets are converted (via interpolation) into a single-receiver equivalent before(More)
Synthetic aperture Sonar (SAS) is a technique for improving sonar resolution by using known sonar motion to lengthen the useful sonar aperture. Unfortunately the images formed with a strip-map SAS are rapidly degraded when there is any perturbation from the known flight-path. This paper outlines a new autofocus procedure for improving SAS imagery, based on(More)
The success of synthetic aperture sonar (SAS) is critically dependent on overcoming several challenges. The sonar has to be positioned with accuracy better than a fraction of a wavelength along the synthetic aperture. The ocean environment, and particularly the sound velocity, has to be accurately estimated for successful focusing of SAS images. For(More)
This paper describes a generalisation of the Phase Gradient Autofocus (PGA) algorithm that allows strip-map operation. A standard autofocus technique, PGA, uses prominent points within the target scene to estimate the point spread function of the system. PGA was developed for tomographic mode spotlight synthetic aperture radar (SAR) but has limited(More)
Successful synthetic aperture sonar (SAS) imaging is dependent of several challenges to be overcome. The sonar has to be positioned with accuracy better than a fraction of a wavelength along the entire synthetic aperture. At 100 kHz this equals an accuracy requirement around 1 millimetre along tens of metres of travelled distance. The ocean environment, and(More)
Collection of synthetic aperture sonar (SAS) data along a circular track and forming a circular SAS (CSAS) image has several benefits over traditional stripmap SAS: the area of interest is observed from all aspect angles giving a better perception; the resolution in the image increases and shadow zones are avoided. Navigation requirements however, become(More)
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