view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Upper Air Research Observatory contour densitometer Dennison, Edwin W. Abstract Observatory contour densitometer. The present Upper Air Research Observatory contour densitometer is a further development of the instrument recently built at the High Altitude Observatory (Fowler, Johnson and Billings, 1953) which was based on a suggestion by H. W. Babcock (1950). The linear resolution is approximately I /~ooth of the linear dimension of the scanned area. This area is seven by seven centimeters on the cathode ray tube and is reduced by a factor of ten to the film or plate being analyzed. This resolution is limited by the smallest illuminated spot which can be produced on the face of the tube. The density resolution is such that two 1S0- photes which differ from each other by 0.03 of a density unit can be just distinguished at a photographic density of two. At a density of one, two isophotes may be drawn which differ by 0.01 of a density unit. This limitation is almost entirely the result of the shot noise resulting from the electronic current at the photocathode of the photomultiplier. Consequently the density resolution can be improved by increasing the brilliance of the cathode ray tube or by increasing the speed of the optical system. Each of these steps has an associated disadvantage, e.g., shortened tube life, critical focusing, etc. Ten seconds are required to make a complete trace, regardless of the complexity of the object. In the design and construction of this instrument the accuracy and resolution have been somewhat compromised in order to achieve the rapid operation. Babcock, H. W. 1950, Pub. A.S.P. 62, iS. Fowler, F. E., D. S. Johnson and D. E. Billings 1953, J. Opt. Soc. Amer. 43, 63. Upper Air Research Observatory, Sunspot, N. Mex. Publication: The Astronomical Journal Pub Date: June 1955 DOI: 10.1086/107187 Bibcode: 1955AJ.....60..157D full text sources ADS |