Forests cover almost a third of world's land surface. Many of them are so vast that the only way to map and study them is from space.
Forests are not only valuable sources of wood and fuel, but they are also home to many types of plants and animals.
Trees also stop wind and rain removing soil, they modify local climate and slow down climate change by storing carbon.
Unfortunately, the forests are rapidly shrinking. Every year, huge areas are destroyed by human activity.
As they fly overhead, satellites can obtain a detailed view of an entire forest in a matter of days. They provide the only quick, easy way to map the ever-changing forests and provide regular updates on their condition.
ESA’s ERS and Envisat spacecraft carry an imaging radar that sees through clouds to reveal changes in the land surface.
A visible-infrared scanner is used to study plant growth and measure surface temperatures. It also detects fires used to clear fields.
Satellites can even pick out different types of tree and show how healthy they are.
Maps based on satellite images help managers and local authorities to protect and preserve the shrinking forests.