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11
Chapitre 1
Introduction
Over the years, climate change and its impact on life have become an alarming question
for science to answer. Historical weather records show evidence of cyclic brutal climate
fluctuations occuring since the formation of Earth and due to volcanic eruptions, meteorite
impacts, solar activity, plate tectonic movements and deviations in the Earth rotational
axis. Today, human industrial activities constitues an extra variable that interfers with
land, ocean and atmosphere natural processes.
To understand, quantifie and model the dynamic interactions between the earth system
components, scientists have to relie on information available over the entire globe with a
satisfactory time frequency. These requirements can only be satisfied by the use of satellite
sensors orbiting the earth at a high altitudes. Multiyear to multidecadal data sets collected
in the ultraviolet, visible, infrared and microwave portions of the energy spectrum, provide
valuable information for researchers to interconnect the Earth’s main geophysical variables.
Nevertheless, the complexity of physical processes involved in global change imposes
data quality standards that satellite instruments fail to meet, despite the continuous technological
innovations in imaging sensors design. Indeed, a given geophysical variable (chlorophyll
concentration for exemple) is determined from raw satellite measurements subsequently
used as input for geolocation, radiometric calibration, atmospheric correction, sun
glint correction, bio-optical models, vicarious calibration, temporal bining...and the list is
certainly not exaustive. This long processing chain makes the estimation of any geophysical
parameter extremely sensitive to initial quantity acquired by satellite instruments.
In simple words, small errors in the instrument response will irreversibly compromise the
accuracy of high level products.
Given the crucial role of oceans in global climate change and the stringent requirements
associated with ocean color remote sensing, space agencies have given high priority
to instrument design and pre-launch/on-orbit calibration procedures. Despite this effort,
many issues related to image quality can still be observed as visual artifacts and require
further processing. These typically include straylight, optical leaks, gaussian noise, speckle
noise (for active sensors), blurring, dead pixels, line dropouts..