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Proceedings Paper

Modeling studies of the MODIS solar diffuser attenuation screen and comparison with on-orbit measurements
Author(s): Eugene Waluschka; Xiaoxiong Xiong; David Moyer; Bruce W. Guenther; William L. Barnes; Vincent V. Salomonson
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Paper Abstract

The MODIS instrument relies on solar calibration to achieve the required radiometric accuracy. This solar calibration occurs as the TERRA spacecraft comes up over the North Pole. The earth underneath the spacecraft is still dark for approximately one minute and the sun is just rising over the earth's north polar regions. During this time the sun moves through about 3.3 degrees, the scan mirror rotates about 19 times and about 50 exposures (frames) are taken each time the field of view is directed to the approximate center (sweet spot) of the solar diffuser. For some of MODIS's bands the brightness of the diffuser is reduced, to prevent detector saturation, by means of a retractable pinhole screen, which produces approximately 600 pinhole images of the sun, within the field of view of any one detector. Previous attempts at creating a radiometric model of this, reduced intensity, calibration scenario produced intensity variations on the focal planes with insufficient detail to be useful. The current computational approach, gets around these limitations and is fast enough to permit simulation of the motion of the sun and the scan mirror. The results resemble the observed focal plane temporal and spatial intensity variations well enough to be useful. The computational approach is described and a comparison with observational data is presented.

Paper Details

Date Published: 26 October 2004
PDF: 12 pages
Proc. SPIE 5542, Earth Observing Systems IX, (26 October 2004); doi: 10.1117/12.560755
Show Author Affiliations
Eugene Waluschka, NASA Goddard Space Flight Ctr. (United States)
Xiaoxiong Xiong, NASA Goddard Space Flight Ctr. (United States)
David Moyer, Science Systems and Applications, Inc. (United States)
Bruce W. Guenther, Univ. of Maryland/Baltimore County (United States)
William L. Barnes, Univ. of Maryland/Baltimore County (United States)
Vincent V. Salomonson, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 5542:
Earth Observing Systems IX
William L. Barnes; James J. Butler, Editor(s)

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