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Proceedings Paper

Comparison of cloud amounts derived from two satellite retrieval techniques
Author(s): Steven A. Ackerman; Martina Kaestner; Karl Theodor Kriebel; H. Mannstein; S. Przybylak
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Paper Abstract

This paper presents a quantitative comparison oftwo cloud detection techniques using satellite observations. The AVHRR (Advanced Very High Resolution Radiometer) Processing scheme Over cLouds Land and Ocean (APOLLO) makes use of five spectral channels with a spatial resolution of I .I km. The Collocated BIRS/2 and AVHRR ProductS (CHAPS) operates with more spectral channels but a lower spatial resolution. To reference the satellite derived cloud amounts, APOLLO results are compared with surface observations of cloud amount. The APOLLO cloud amount and surface observations of cloud cover are generally within over vegetated surfaces. Over oceans, the agreement in total cloud cover between the two satellite techniques is very good (r=O.92). Application of a dependent sample i-test to the two cloud amount data sets indicates that there is a greater than 99.9% probability that the two samples were drawn from the same population. This demonstrates that the subsampling of AVHRR pixels in the CHAPS processing is appropriate for deriving cloud amounts over a 2.5degree oceanic region. For such a region there is a tendency for CHAPS to derive higher cloud amounts than APOLLO. This is attributed to differences in clear-sky radiance thresholds derived from the CHAPS spatial variability test. Over land, the derived cloud amount products from the two methods are considerably different. The CHAPS product is an effective cloud amount defined for each HIRS field ofview which is the product of cloud fraction and cloud emissivity rather than a simple areal percentage. Also, the HIRS/2 footprint size (17 km at nadir) is much larger than that of the AVHRR. There is a good correlation of the two cloud products (r=O.82); however, a t-test indicates the two techniques are deriving fundamentally different parameters. This is consistent with the above differences. Recommendations for improving the two cloud retrieval techniques are suggested.

Paper Details

Date Published: 27 December 1995
PDF: 12 pages
Proc. SPIE 2578, Passive Infrared Remote Sensing of Clouds and the Atmosphere III, (27 December 1995); doi: 10.1117/12.228939
Show Author Affiliations
Steven A. Ackerman, Univ. of Wisconsin/Madison (United States)
Martina Kaestner, DLR (Germany)
Karl Theodor Kriebel, DLR (Germany)
H. Mannstein, DLR (Germany)
S. Przybylak, DLR (Germany)

Published in SPIE Proceedings Vol. 2578:
Passive Infrared Remote Sensing of Clouds and the Atmosphere III
David K. Lynch; Eric P. Shettle, Editor(s)

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