lmd_Seze1997.bib
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@comment{{Command line: /usr/bin/bib2bib --quiet -c 'not journal:"Discussions"' -c 'not journal:"Polymer Science"' -c ' author:"Seze" or author:"Sèze" ' -c year=1997 -c $type="ARTICLE" -oc lmd_Seze1997.txt -ob lmd_Seze1997.bib /home/WWW/LMD/public/Publis_LMDEMC3.link.bib}}
@article{1997JApMe..36..664G,
author = {{Giraud}, V. and {Buriez}, J.~C. and {Fouquart}, Y. and {Parol}, F. and
{Seze}, G.},
title = {{Large-Scale Analysis of Cirrus Clouds from AVHRR Data: Assessment of Both a Microphysical Index and the Cloud-Top Temperature.}},
journal = {Journal of Applied Meteorology},
year = 1997,
month = jun,
volume = 36,
pages = {664-675},
abstract = {{An algorithm that allows an automatic analysis of cirrus properties from
Advanced Very High Resolution Radiometer (AVHRR) observations is
presented. Further investigations of the information content and
physical meaning of the brightness temperature differences (BTD) between
channels 4 (11 m) and 5 (12 m) of the radiometer have led to the
development of an automatic procedure to provide global estimates both
of the cirrus cloud temperature and of the ratio of the equivalent
absorption coefficients in the two channels, accounting for scattering
effects. The ratio is useful since its variations are related to
differences in microphysical properties. Assuming that cirrus clouds are
composed of ice spheres, the effective diameter of the particle size
distribution can be deduced from this microphysical index.The automatic
procedure includes first, a cloud classification and a selection of the
pixels corresponding to the envelope of the BTD diagram observed at a
scale of typically 100 {\times} 100 pixels. The classification, which
uses dynamic cluster analysis, takes into account spectral and spatial
properties of the AVHRR pixels. The selection is made through a series
of tests, which also guarantees that the BTD diagram contains the
necessary information, such as the presence of both cirrus-free pixels
and pixels totally covered by opaque cirrus in the same area. Finally,
the cloud temperature and the equivalent absorption coefficient ratio
are found by fitting the envelope of the BTD diagram with a theoretical
curve. Note that the method leads to the retrieval of the maximum value
of the equivalent absorption coefficient ratio in the scene under
consideration. This, in turn, corresponds to the minimum value of the
effective diameter of the size distribution of equivalent Mie
particles.The automatic analysis has been applied to a series of 21
AVHRR images acquired during the International Cirrus Experiment
(ICE'89). Although the dataset is obviously much too limited to draw any
conclusion at the global scale, it is large enough to permit derivation
of cirrus properties that are statistically representative of the cirrus
systems contained therein. The authors found that on average, the
maximum equivalent absorption coefficient ratio increases with the
cloud-top temperature with a jump between 235 and 240 K. More precisely,
for cloud temperatures warmer than 235 K, the retrieved equivalent
absorption coefficient ratio sometimes corresponds to very small
equivalent spheres (diameter smaller than 20 m). This is never observed
for lower cloud temperatures. This change in cirrus microphysical
properties points out that ice crystal habits may vary from one
temperature regime toanother. It may be attributed to a modification of
the size and/or shape of the particles.
}},
doi = {10.1175/1520-0450-36.6.664},
adsurl = {http://adsabs.harvard.edu/abs/1997JApMe..36..664G},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
