Page last updated: 15 May 2008
by James Painter, BBC's Latin America Analyst
The most advanced satellite technology in the world is being put to use to detect the Amazon's deforestation in Brazil.
To monitor the destruction of the forest, the Brazilian government is employing two systems - Prodes and Deter, both under the management of the National Institute for Space Research, INPE.
Officials can view on their computers high resolutions of small sections of the Amazon based on a series of polygons. They say they can detect instantly the trees being felled and send in teams on the ground to make arrests.
Prodes - an acronym for Programme to Calculate Deforestation in the Amazon - produces the most accurate images for calculating the annual rate of forest loss.
It takes as its reference point data collected in August, in the dry season when pictures are clearest. Its level of precision is that it can detect areas of deforestation of more than 6.5 hectares, the equivalent of eight football fields.
Meanwhile, Deter stands for Real-time Detection of Deforestation. It acts as an alert system throughout the whole year. Every fortnight, it sends a report to IBAMA, Brazil's environmental protection agency, detailing the areas of deforestation it has detected. It can detect an area of deforestation of greater than 25 hectares, or 30 football fields. For example, Deter detected an area of deforestation of 3,235 square kilometres in the last five months of 2007.
As Deter is estimated to detect between 40 and 60 per cent of what Prodes can capture, researchers doubled the Deter figures to arrive at more than 7,000 square kilometres.
The two systems rely mainly on images provided by the Modis sensor on board the Landsat 5 satellite of Nasa, and from the WFI sensor on board the CBERS-2 (the China-Brazil Earth Resources Satellite).
However, both systems have some limitations.
The level of cloud cover that can impede detection, while it is difficult to know exactly when the deforestation took place because of the delays in receiving the images.
But the main obstacle is the resources available to follow up the information the systems provide. In the whole of the Amazon region there are about 640 government inspectors and other officials, and just four helicopters.
And even when an alert goes out, it is very difficult to find out who exactly on the ground is responsible for the deforestation, partly because it is difficult to establish who owns which piece of land.