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  • 11
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    Errors in Hadamard spectroscopy or imaging caused by imperfect masks (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An analysis is given of the errors in Hadamard spectroscopy that are caused by transparent slits in the mask being systematically wider or else narrower than they should be. It is shown that if the input spectrum consists of a single line, the distorted spectrum that is actually calculated consists of this line, plus four small blips. When the transparent slits are too wide, these blips are of equal height and the same sign, one pair surrounding the line, and another pair displaced a certain distance from it. When the slits are too narrow, the displaced blips have the same amplitude but are negative.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-142932
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 12
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    A practical Hadamard transform spectrometer for astronomical application (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The mathematical properties of Hadamard matrices and their application to spectroscopy are discussed. A comparison is made between Fourier and Hadamard transform encoding in spectrometry. The spectrometer is described and its laboratory performance evaluated. The algorithm and programming of inverse transform are given. A minicomputer is used to recover the spectrum.
    Keywords: ASTRONOMY
    Type: NASA-CR-149790 , CRSR-655
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 13
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    Fourier and Hadamard transform spectrometers - A limited comparison (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An encoding figure of merit is established for a detector-noise limited Fourier transform spectrometer (FTS) and compared to the comparable figure for a Hadamard transform spectrometer (HTS). The limitation of the Fourier system is partly that it does not truly Fourier analyze the radiation. Instead a cosine squared modulation is imposed on the different spectral frequencies. An additional difficulty is that neither the cosine nor the cosine squared functions form an orthonormal set. This makes the Fellgett's advantage (root-mean-squared figure of merit) for a single detector Michelson interferometer a factor of the square root of (N/8) greater than for a conventional grating instrument - rather than the square root of (N/2). The theoretical limit would be the square root of N.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 15; Nov. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 14
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    Systematic errors in Hadamard transform optics (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Error sources encountered in Hadamard transform optical instruments are discussed. Such errors are caused by factors including moving masks, incorrect mask alignment, defects in mask fabrication, missing data, drifts in background level, and diffraction. Techniques for error reduction and/or elimination are described for each of the cases considered. It is noted that the errors described occur in singly encoded spectrometers and imagers.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 17; Sept. 15
    Format: text
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    NASA TECHNICAL REPORTS
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