Potential of Optical Fourier Analysis for Measuring Windscreen Distortion.
AIR FORCE AEROSPACE MEDICAL RESEARCH LAB WRIGHT-PATTERSON AFB OH
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The potential of an optical Fourier technique for measuring the optical distortion of aircraft windscreens was examined. It was hypothesized that the compactness of the harmonics of the optical Fourier transforms of vertical and horizontal square wave targets photographed through windscreens would correlate highly with distortion in photographs of a gridboard. Eleven transparent optical distortion panels were used to produce gridboard pictures and vertical and horizontal transform pictures. Gridboard pictures were subjectively ranked by 23 observers for amount of optical distortion. Transform pictures were ranked for compactness of the third harmonic. All three picture sets were also measured by subjective magnitude estimation. Rank correlation between gridboard photograph distortion ranks and compactness ranks for the vertical Fourier transform was .950. Overall rankings of gridboard distortion photographs and compactness rankings was .977. Such high statistically significant correlations show that distortion judgements from gridboard photographs is accurately predictable from judged compactness of the third harmonic. Thus, the Fourier method may be useful for measuring optical distortion. Development of objective methods to measure the compactness and to calibrate such measures against conventional measurements is warranted. This development would lead to a rapid, accurate and objective method for measuring the optical distortion of aircraft windscreens. Author
- Ceramics, Refractories and Glass