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Positive-feedback photometric drift in the PDSDigitizing flatfield images produces conditions in the Photometric Data System PDS which cause the measured density to drift by as much as .1 DN during a 10 minute interval. The drift occurs when the PDS, set up in equilibrium at fog level, subsequently scans a reasonably dense region for periods of longer than a few minutes. The drift is manifested primarily as a positive shift in density that is approximately the same for all densities. If the fog level is assumed to be in fact constant and is monitored during scans of flat fields, the PDS drift may be removed by subtracting the difference between the observed fog level and its assumed constant value for each pixel. This function is then smoothed and subtracted, as a function of scan line, from the measured density. The fog level is then adjusted to a standard value by adding a constant. The result is a flattened scan with PDS drift removed to the accuracy within which the fog level drift matches the drift at other levels.
Document ID
19840019956
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Cornett, R. H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Bohlin, R. C.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hill, J. K.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Stecher, T. P.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 12, 2013
Publication Date
July 1, 1984
Publication Information
Publication: Astron. Microdensitometry Conf.
Subject Category
Instrumentation And Photography
Accession Number
84N28025
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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