Methods for Correction of Refractive Errors.
Annual rept. 1 Jan-31 Dec 83,
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Research to improve the modelling of scattered fields from an object is described. These computer models can then be used to gain a better understanding of the errors in first order diffraction tomography and to help guide research in designing better algorithms for estimating cross sectional images. Two approaches are described to more accurately model the scattered fields from objects other than simple cylinders. Twerskys multiple scattering theory was used to investigate the scattering caused by multiple objects. By decomposing the first order scattered field into its plane wave components, the second order scattered field can be calculated by scattering each plane wave with each object. Using this computational procedure, we have shown that even when each component of a two component object is weakly scattering, the multiple scattering effects become important if the components are blocking each other. A more general approach than this method is possible if the Born integral is solved using an iterative procedure. This approach can be considered a generalization of the Twersky theory and works for arbitrary objects. Since it is an iterative procedure, its region of convergence is very important and we discuss its validity using computer simulations.
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