Accession Number : ADA273851

Title :   Numerical Simulation of Tomographic Reconstruction for the Study of Turbulence Using Optical Wavefront Sensor Measurements.

Descriptive Note : Master's thesis,

Corporate Author : AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING

Personal Author(s) : Johnson, Robert L.

Report Date : DEC 1993

Pagination or Media Count : 82

Abstract : The optical quality of a coherent beam passing through a turbulent flow layer can be severely degraded by phase errors. The principle goal of this research is to model the use of wavefront sensor measurements and computed tomography to reconstruct refractive index distributions of transparent objects for the study of turbulent flows. Tomography is the processing of measurements of one-dimensional line integrals through a two-dimensional function to reconstruct a two-dimensional estimate of the function. A least-squares wavefront phase reconstructor is modeled using Zernike polynomials and triangle functions as elementary functions for the reconstructor. Two tomographic reconstruction algorithms are implemented: (1) iterative reconstruction and (2) filtered back-projection. Through numerical simulation, the effects of undersampling and limited wavefront sensor resolution are studied. Distorted wavefront data are generated by performing line integrals through known objects with different numbers and ranges of view angle. Wavefront reconstruction is applied using varying resolution. Two tomographic reconstruction methods are employed and comparisons are made with the original known objects. Results show that a least-squares wavefront reconstructor using triangle functions provides better results. Increasing the number and range of view angles generally improves the quality of the tomographic reconstruction. Furthermore, iterative tomographic reconstruction techniques prove superior when limited data are available. Optical tomography, Computed tomography, Wavefront reconstruction, Flow visualization, Three-dimensional reconstruction

Descriptors :   *REFRACTIVE INDEX, *TURBULENT FLOW, *WAVEFRONTS, *MATHEMATICAL MODELS, *COMPUTERIZED TOMOGRAPHY, ALGORITHMS, ANGLES, COMPARISON, ERRORS, ESTIMATES, FLOW VISUALIZATION, INTEGRALS, LAYERS, MEASUREMENT, ONE DIMENSIONAL, PHASE, POLYNOMIALS, QUALITY, RESOLUTION, SIMULATION, THREE DIMENSIONAL, TOMOGRAPHY, TRIANGLES, TWO DIMENSIONAL, THESES.

Subject Categories : Fluid Mechanics
      Optics

Distribution Statement : APPROVED FOR PUBLIC RELEASE