Envisat, keeping a vigil on the planet
Monitoring the ozone layer
The ozone layer is a natural barrier in the stratosphere, 25 to 35 kilometres above our heads, which filters ultraviolet radiation from the sun. This barrier is of vital importance because it protects us from burns and skin cancer.
However, indicators clearly show that the ozone layer is suffering from numerous "holes". Greenhouse gases, which activate chlorine compounds (CFCs) released into the atmosphere, lead to ozone depletion, and are the protective layer's number one enemy.
New international regulations should contribute to reductions in the use of CFCs, but even so, conditions will not return to normal until the middle of the century.
Envisat measurements will enable agencies to verify that international agreements are respected and to prepare the next regulatory steps in this field.
Evolution of the hole in the ozone layer between September 2002, viewed by the GOME instrument aboard ERS-2, and September 2003, by the MIPAS instrument aboard Envisat. Crédits: BIRA-IASB
Understanding the oceans' dynamic processes
Sea-surface temperatures around Crete, recorded by the AATSR instrument on Envisat, August 2003. The highest temperatures recorded are 25°C (red), the lowest are below 22°C (green). Crédits : ESA
Observation from space, particularly with the French-US altimetry satellites Topex/Poseidon and Jason-1, has lifted the veil on these highly complex phenomena. The best known is El Niño, whose effects are felt around the world, bringing drought or torrential rains.
Envisat, thanks to its capacity for detailed observation, is a valuable complement to the systems already in place for analysing and modelling oceanic behaviour. As a result, the seas will soon reveal their secrets of temperature, water colour, wind speed and direction to oceanographers.
Slowing down global warming
What is the greenhouse effect? It involves the accumulation of certain gases which hold heat within the atmosphere. Above all, it is a natural phenomenon enabling the Earth—150 million kilometres from the Sun—to maintain a temperature that supports life, at about 18° Celsius.
The danger comes from the acceleration of this natural phenomenon by human activities, leading to a gradual warming of the planet. In specific terms, this means that within the next century, 50 countries will be threatened with an average rise in sea levels of 50 cm. The Kyoto accord of 1997, signed by 55 countries, calls for an 8% reduction in greenhouse gases by 2012.
Envisat will make it possible to verify these objectives, as well as to better understand the interactions between the atmosphere, the oceans and the biosphere.
