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Proceedings Paper

MODIS cloud mask: current situation and its improvements
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Paper Abstract

The 36 channel Moderate Resolution Imaging Spectroradiometer (MODIS) offers the opportunity for multispectral approaches to cloud detection. The MODIS cloud mask developed at the Cooperative Institute for Meteorological Satellite Studies (CIMSS) uses several cloud detection tests to indicate a level of confidence that the MODIS is observing clear skies. The MODIS cloud mask algorithm identifies several conceptual domains according to surface type and solar illumination, including land, water, snow/ice, desert, and coast for both day and night. The updated cloud mask has many improvements, such as improved cloud/surface discrimination over desert regions, sun glint processing and thin cirrus detection. For non-snow-covered land areas, a clear sky confidence of 0.96 (probably clear) will be assigned if thresholds are met for three tests: 3.9-11 μm and 3.75-3.9 μm brightness temperature differences and a 1.24/0.55 μm reflectance ratio test. Values of these must be <15K, <11K and >2.0, respectively. A change has been made to the NIR (band 2) reflectance test for sun glint processing. The updated method is to calculate a cloud threshold as a linear function of sun-glint angle in three separate ranges. A new clear-sky restoral test was added where the ratio of band 17/18 reflectance is utilized to discriminate between low clouds and water surfaces. The thin cirrus thresholds using corrected band 26 (1.38 μm) reflectances were also modified.

Paper Details

Date Published: 16 June 2003
PDF: 6 pages
Proc. SPIE 4895, Applications with Weather Satellites, (16 June 2003); doi: 10.1117/12.466824
Show Author Affiliations
Hong Zhang, Univ. of Wisconsin/Madison (United States)
Richard A. Frey, Univ. of Wisconsin/Madison (United States)
Steven A. Ackerman, Univ. of Wisconsin/Madison (United States)
Liam Gumley, Univ. of Wisconsin/Madison (United States)
Kathy Strabala, Univ. of Wisconsin/Madison (United States)
W. Paul Menzel, National Oceanic and Atmospheric Administration (United States)

Published in SPIE Proceedings Vol. 4895:
Applications with Weather Satellites
W. Paul Menzel; Wen-Jian Zhang; John Le Marshall; Masami Tokuno, Editor(s)

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