Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
6
12
2006
10.5194/acp-6-4461-2006
http://www.atmos-chem-phys.net/6/4461/2006/
http://www.atmos-chem-phys.net/6/4461/2006/acp-6-4461-2006.html
http://www.atmos-chem-phys.net/6/4461/2006/acp-6-4461-2006.pdf
4461
4476
2006-10-05
The Heidelberg iterative cloud retrieval utilities (HICRU) and its application to GOME data
M. Grzegorski
mgrzegor@iup.uni-heidelberg.de
M. Wenig
U. Platt
P. Stammes
N. Fournier
T. Wagner
Institute of Environmental Physics, University of Heidelberg, Germany
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
KNMI, Climate Research and Seismology Department, de Bilt, The Netherlands
Information about clouds, in particular the accurate
identification of cloud free pixels, is crucial for the retrieval
of tropospheric vertical column densities from space. The
Heidelberg Iterative Cloud Retrieval Utilities (HICRU) retrieve
effective cloud fraction using spectra of two instruments designed
for trace gas retrievals from space: The Global Ozone Monitoring
Experiment (GOME) on the European Remote Sensing Satellite (ERS-2)
and the SCanning Imaging Absorption SpectroMeter for Atmospheric
CHartographY (SCIAMACHY) on ENVISAT.
<P>
HICRU applies the widely used threshold method to the so-called
Polarization Monitoring Devices (PMDs) with higher spatial
resolution compared to the channels used for trace gas retrievals.
Cloud retrieval and in particular the identification of cloud free
pixels is improved by HICRU through a sophisticated, iterative
retrieval of the thresholds which takes their dependency on
different instrumental and geometrical parameters into account.
The lower thresholds, which represent the surface albedo and
strongly affect the results of the algorithm, are retrieved
accurately through a four stage classification scheme using image
sequence analysis.
<P>
The design and the results of the algorithm applied to GOME data
are described and compared to several other cloud algorithms for
GOME. The differences to other cloud algorithms are discussed with
respect to the particular characteristics of the algorithms.
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