Biosphere

The biosphere is a very special sphere compared with the others. It is not simply governed by the laws of physics: the laws of the living world also affect how it works. It is home to living organisms, from prions to humans, and from plants to animals. It is the sphere of life. The biosphere in the strict definition of the term, which includes plants and animals, colonizes all the physical spheres. In the hydrosphere, it is present in the form of fish, plankton etc. In the atmosphere, birds, etc. And on the surface of the continents, it takes the shape of vegetation, such as virgin tropical forest, savanna and tundra.

By their practices, their social organization, their representations and their needs, which are heavily infl uenced by population growth, humans have gradually broken loose from the biosphere, forming a new sphere, the anthroposphere. This includes societies and the expression of their needs. It is mirrored by a technosphere which includes all human practices and techniques (agriculture, irrigation, etc), infrastructures (roads, cities, etc), and the alteration of the biosphere by humans on all scales, from the local to the global. In order to study, analyse, understand and monitor this complex biosphere, where all the interactions between the physical and human spheres take place, satellites are especially suitable tools.

They can be equipped with the whole range of sensors and remote sensing methods available: visible and infrared imaging radiometers to classify vegetation and its state, microwave imagers to characterize the stat of soils, and active synthetic aperture radar instruments to observe the roughness of surfaces and of vegetation. All this gives measurements with spatial resolutions of a few metres or even a metre, which is quite a technological achievement.