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Chapitre 2
Remote Sensing with MODIS
2.1 The evolution of remote sensing
Look far and wide... This could well have been one of the underlying rules used by
evolution to produce life as we can see it all over the Earth. From the multiple eyes of
arachnophibia species to the mobile stereoscopic eyes of the chameleon, nature offers a
variety of elegant examples. The very origin of hominid bipedism have been investigated
by many evolutionnary scientists and attributed to a survival need. The ability to stand
on two feet in the hostile environment of prehistory, enabled early Homo-Sapiens to look
beyond savanna’s high grasses and thus avoid any uncomfortable encounters.
Jumping back to comtemporary times, the numerous satellites orbiting the earth can
be also perceived as the result of a long-term survival instinct. Remote sensing aims at
measuring information and determining specific properties of an object or phenomenon
without direct physical contact. Today, this term commonly refers to the set of techniques
used to derive geophysical variables of the Earth (or other planets, stars, galaxies...).
The development of remote sensing is a direct consequence of the technological advances
made in aviation from the begining of twentieth century. The first and second world war
triggered an interest in aviation strong enough to attract heavy investments from most of
the countries involved in war. Planes were not only used as a fast transportation vehicule,
but were also considered a strategic advantage for their ability to monitor simultaneously
wide spatial areas. The invasion of Normandie is a good illustration of how planes were
put to contribution. Aerial photographes were taken and analysed to establish appropriate
landing surfaces and determine the depth and state of coastal waters. More significantly,
infrared filters were already included in the primitive imaging devices to distinguish natural
vegetation from enemy camouflages. The following steps towards modern remote sensing
were achieved as consecutive technological intimidation attempts between USA and USSR
during the cold war, leading to a brutal race to space ; Spoutnik and Explorer, quickly
followed by the creation of NASA, the first men on the moon and the first habited spatial
station (Saliout-1).