Error correction in images and imaging instruments.
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
A ray optical method is described which enables the subreflector of a Cassegrain antenna to be redesigned to compensate for measured errors in the main reflector surface. The method ensures that the redesigned subreflector is correctly positioned relative to the main reflector which in turn ensures that the antenna has a high aperture efficiency. The data specifying the redesigned subreflector is arranged in a form suitable for subsequent manufacture. An efficient method is described which provides a check that the performance of the antenna incorporating the redesigned subreflector is satisfactory. A method of interpolation, using Lagrange polynomials of a complex variable, has been implemented, which permits two-dimensional interpolation to be accomplished efficiently as well as accurately when the grid of points on which the data is available, is irregular. A new technique called "speckle mask processing” is described and its successful simulation in the optical laboratory, using both optical and digital processing methods, is reported. This technique should permit a distorted version of the true image of a cluster of stars to be obtained, even when viewed through the earth’s turbulent atmosphere. A new pattern reconstruction procedure is described. It is shown how the limited information contained in the distorted image is usually sufficient to permit the object to be restored, by speckle mask processing, virtually unambiguously from its autocorrelation, which can always be recovered accurately by Labeyrie's original form of speckle interferometry.