Fourier Modulus Image Construction.
Final technical rept. 7 Sep 79-30 Sep 80,
ENVIRONMENTAL RESEARCH INST OF MICHIGAN ANN ARBOR RADAR AND OPTICS DIV
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This report describes the investigation of a new method for recovering diffraction-limited images through the turbulent atmosphere. It consists of an iterative algorithm that constructs an image from Fourier modulus data which is measured by stella speckly interferometry. Research results indicate that the method has the potential for providing diffraction-limited images of earth-orbiting satellites. Image construction experiments were performed on Fourier modulus data computer-simulated to include the effects of atmospheric turbulence, diffraction, photon Poisson statistics noise, and a finite number of short-exposure images. The quality of the constructed images was found to degrade in a gradual and predictable manner as the signal-to-noise ratio decreases. The rms error of the constructed images was found to vary approximately as the square root of the rms error of the Fourier modulus data. Diffraction-limited images were constructed for levels of photon noise that would be expected for imaging satellites through a 1.6-meter telescope. Image construction experiments were performed on the Fourier modulus of a number of different objects of varying complexity. Interpretation of the results was complicated by a tendency of the algorithm to stagnate at local minimum having the appearance of a good quality image superimposed by a pattern of stripes. Nevertheless, results were suggestive that the solution is usually unique.
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