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  • INSTRUMENTATION AND PHOTOGRAPHY  (10)
  • 1975-1979  (10)
  • 1960-1964
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Year
  • 1
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    Errors in Hadamard spectroscopy or imaging caused by imperfect masks (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: An analysis is given of the errors in Hadamard spectroscopy that are caused by transparent slits in the mask being systematically wider or 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 with one pair surrounding the line and another pair 5isplaced a certain distance from it. When the slits are too narrow, the displaced blips have the same amplitude, but are negative. The response to an arbitrary input spectrum is then determined from this. The same method of analysis may also be used to handle other types of errors.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 14; Nov. 197
    Format: text
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  • 2
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    Fourier and Hadamard transform spectrometers - A limited comparison. II (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A mathematical approach was used to compare interferometric spectrometers and Hadamard transform spectrometers. The principle results are reported, noting that the simple Hadamard spectrometer encodes more efficiently than a Michelson interferometer which, in turn, encodes less efficiently than is usually acknowledged. Hirschfeld's (1977) major objections to these findings are discussed, although it is noted that none of his objections is supported by evidence.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 16; Dec. 197
    Format: text
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  • 3
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    Practical multi-spectrum Hadamard transform spectrometer (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Specifications of a new Hadamard transform spectrometer for infrared astronomical applications are presented. The instrument has 15 entrance slits and 255 exit slits. Data can be gathered at the rate of up to five readings per second so that the entire spectral run lasts some thirteen minutes. The data is processed in real time by a minicomputer. At the end of the thirteen minute run the spectrum is available for immediate viewing on a CRT display. The spectra can be punched and stored on paper tape for later processing.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 14; Oct. 197
    Format: text
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  • 4
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    Development and evaluation of a Hadamard transform imaging spectrometer and a Hadamard transform thermal imager (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A spectrometric imager and a thermal imager, which achieve multiplexing by the use of binary optical encoding masks, were developed. The masks are based on orthogonal, pseudorandom digital codes derived from Hadamard matrices. Spatial and/or spectral data is obtained in the form of a Hadamard transform of the spatial and/or spectral scene; computer algorithms are then used to decode the data and reconstruct images of the original scene. The hardware, algorithms and processing/display facility are described. A number of spatial and spatial/spectral images are presented. The achievement of a signal-to-noise improvement due to the signal multiplexing was also demonstrated. An analysis of the results indicates both the situations for which the multiplex advantage may be gained, and the limitations of the technique. A number of potential applications of the spectrometric imager are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-145036 , ASE-3851
    Format: application/pdf
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  • 5
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    A practical multi-spectrum Hadamard Transform Spectrometer (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A Hadamard Transform Spectrometer (HTS) which simultaneously obtains fifteen infrared spectra, each having 255 spectral elements was constructed. Spectra are obtained essentially in real time through use of a minicomputer with 8K words of memory and a CRT display. This permits operation of the instrument in the field.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-142649
    Format: application/pdf
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  • 6
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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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  • 7
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    Masks for Hadamard transform optics, and weighing designs (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: This paper gives a brief survey of the design of masks for Hadamard spectrometers and image scanners. Three different criteria are described for judging a mask, as well as techniques for choosing masks that are not too far from the optimum.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 15; Jan. 197
    Format: text
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  • 8
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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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  • 9
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    Hadamard transform imager and imaging spectrometer (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An imager and a spectrometric imager, which achieve multiplexing by the use of binary optical encoding masks, have been built and tested. The masks are based on orthogonal, pseudorandom digital codes derived from Hadamard matrices. The spatial (and/or spectral) data are therefore obtained in the form of a Hadamard transform of the spatial (and/or spectral) scene. Computer algorithms are used to decode the data and reconstruct images of the original scene. The hardware, algorithms processing and display facility are described. A number of spatial and spatial/spectral images, obtained in the laboratory, are presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Format: text
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  • 10
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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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