What's it for?
Envisat and satellites for observing Earth
Remote sensing satellites, also known as Earth observation satellites, have their eyes and ears pointed at our beautiful planet. To achieve scientific progress, improve economic performance or provide military intelligence, they are indispensable for the protection of our planet and the safety of its inhabitants. Envisat is one of the largest and most sophisticated of these devices.
© ESA/A.Van Der Geest
HOW DOES IT WORK?
These satellites are equipped with hypersensitive sensors that are able to record the main electromagnetic movements emanating from the area under observation. The advantage of satellites is that they see better than we do by sweeping the entire electromagnetic spectrum, from radio frequencies through to hyper frequencies, by way of infrared and ultraviolet*. Then by analysing the radiation we can work out which body sent it to us, even if we are very far away from it. As they are located outside of the atmosphere that filters large amounts of the electromagnetic spectrum, satellites can distinguish between radiation from snow, a cloud or even the energy of a long dead star…The satellite is only “receiving”: it can also ask questions to objects, using radars that “throw” a signal at them.
Low orbits are the star turn
It’s easy to understand. If you want to observe the Earth with the highest resolution possible, you had better not be too far away. Polar orbits, for example, are very useful since they let a satellite “cover” the entire planet in very little time. “Envisat”, the amazing European satellite designed by the European Space Agency and built under the management of EADS Astrium, makes use of them. This is one of the biggest satellites ever launched by the Europeans. At 8,200 kg it is the size of an articulated lorry.
Infinite applications
In Envisat we have a striking example of the possible uses for this type of satellite. Using ten scientific instruments, each specialised in the analysis of part of the electromagnetic spectrum, it informs people on Earth about the chemistry of the atmosphere (the ozone layer), oceanography (marine biology, the colour and temperature of the ocean, waves), hydrology (soil moisture, flooding), monitoring agriculture and forestry, natural risks, monitoring of seaborne traffic, monitoring pollution and global warming, and even monitoring epidemics, noting favourable conditions for the reproduction of mosquitoes, the carriers of disease!
