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Title
Mesures physiques et signatures en télédétection

preliminary correction should provide a better consistency of the data, both in time and space. Corrected
global data sets are to be further analyzed, either for quantitative studies (e.g. Maisongrande et al. 1994) or in
order to assess their accuracy, for example using well-documented test sites.
In the future, atmospheric effects could be accounted for in a better way by using additional data sets
either from atmospheric global circulation model analysis or provided by existing (e.g. TOMS) or new sensors
(e.g. MODIS, POLDER). Pr omising methods are now being developed to normalize bidirectional reflectances
(Cabot and Dedieu, 1993, Leroy and Roujean, 1994). More work is needed to improve compositing techniques
(Qi and Kerr, 1994), since it is well known that MVC favours large scan angles. Also MVC is not well suited
to fit bidirectional reflectance models with satellite measurements. Finally, improvements of system features
such as orbit control, constant resolution over the whole field of view, and of preprocessing performance
(geometric corrections, cloud screening, calibration monitoring) is a prerequisite to higher level corrections
(atmosphere, surface anisotropy).
ACKNOWLEDGEMENTS
This work is a contribution to the ESCOBA project "The global carbon cycle and its perturbation by man and
climate n. Part B: terrestrial biosphere", supported by the Environment Program of the Commission of the
European Communities.
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MONITORING P
LERTS, Unité ]
Monitoring of the calil
various studies, involv
Nevertheless, most of
particularly the need f<
monitoring of the gain (
The method that we de
contribute to the mea;
evolution. Directional e
the season. At last, one
cyclical behavior and
describing atmospheric
over long term period,
atmospheric water vapc
This method has been
considering each senses
1. INTRODUCTION
Throughout the last ye!
problems and gain dri
especially in shortwave
In order to solve such a
get a realistic gain va
approximately), atmosp
The atmospheric and di
effectively to the g ain d
effects is their time peri
of the non-lambertian
expected to follow quiti
The method presented 1
time period, and whei
continuously monitor tl
been selected and obse
stability. Some of thes
complete an intercalibri
2. DATA SET
The data set we used v
Atmospheric Administ
infrared channels, brig]
satellites, subsampled t
launched in September
40