7,410 research outputs found
Geometry parameter estimation for sparse X-ray log imaging
We consider geometry parameter estimation in industrial sawmill fan-beam
X-ray tomography. In such industrial settings, scanners do not always allow
identification of the location of the source-detector pair, which creates the
issue of unknown geometry. This work considers an approach for geometry
estimation based on the calibration object. We parametrise the geometry using a
set of 5 parameters. To estimate the geometry parameters, we calculate the
maximum cross-correlation between a known-sized calibration object image and
its filtered backprojection reconstruction and use differential evolution as an
optimiser. The approach allows estimating geometry parameters from full-angle
measurements as well as from sparse measurements. We show numerically that
different sets of parameters can be used for artefact-free reconstruction. We
deploy Bayesian inversion with first-order isotropic Cauchy difference priors
for reconstruction of synthetic and real sawmill data with a very low number of
measurements
Speckle interferometry
We have presented the basic mathematical treatment of interferometry in the
optical domain. Its applications in astronomical observations using both the
single aperture, as well as the diluted apertures are described in detail. We
have also described about the shortcomings of this technique in the presence of
Earth's atmosphere. A short descriptions of the atmospheric turbulence and its
effect on the flat wavefront from a stellar source is given. The formation of
speckle which acts as carrier of information is defined. Laboratory experiments
with phase modulation screens, as well as the resultant intensity distributions
due to point source are demonstrated. The experimental method to freeze the
speckles, as well as data processing techniques for both Fourier modulus and
Fourier phase are described. We have also discussed the technique of the
aperture synthesis using non-redundant aperture masks at the pupil plane of the
telescope, emphasizing set on the comparison with speckle interferometry. The
various methods of image restoration and their comparisons are also discussed.
Finally, we have touched upon certain astrophysical problems which can be
tackled with the newly developed speckle interferometer using the 2.34 meter
Vainu Bappu Telescope (VBT), situated at the Vainu Bappu Observatory (VBO),
Kavalur, India.Comment: 32 pages tex files including figure
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