Rio De Janeiro -- The Brazilian Amazon, with a third of the world's tropical forests, has been under strict surveillance, thanks to the new Amazon surveillance system, known as Sivam.

The jungle region contains one third of the biodiversity of the earth, including the world's largest freshwater source, and is thus one of the most important strategic resources for the 21st century.

And while Brazil seeks to preserve its natural patrimony though its position as a developing economy impacts on its environment, its military is especially ticklish when it comes to national sovereignty over the Amazon.

In the build-up to the 2002 earth summit in Johannesburg, Brazil is adamant that the Rio accords, formulated here 10 years ago at the last earth summit, should in no way be modified, and still wants to see the Kyoto Protocol brought in, complete with its targets to cut pollutants and use more renewable energy.

"Protecting the Amazon, with the support of our society and the increased military presence, is one of the priorities of current defense policy," the Ministry of Defense has said.

Sivam, which monitors an area of 5.5 million square kilometers (2.12 million square miles) -- about the size of western Europe -- will alert authorities to incursions from neighboring countries, particularly Colombia, where leftist guerrillas fighting a civil war have clashed with Brazilian troops.

More than 4,000 Brazilian soldiers and sailors equipped with amphibious tanks, patrol boats and helicopters, are posted along the border.

The system, headquartered in Brasilia, also has five radar aircraft and 25 fighter jets at its disposal. It is also aimed at reducing drug trafficking by monitoring all flights over the Amazon, allowing authorities to search out and destroy secret landing strips.

The surveillance system dovetails with a law passed in 1998 by the Brazilian Congress allowing the Brazilian air force to shoot down planes that refuse to identify themselves or refuse to land when asked, according to AFP.

The system's 120 "eyes" will also help to protect the Amazon environment by better monitoring deforestation, illegal exploitation of protected substances, and violence against indigenous tribes.

Sivam, launched in 1994, drew controversy after the U.S. Raytheon company beat out Thomson-CSF of France for the contract. News reports accused military officials and politicians of throwing the contract to a U.S. company to curry favor with Washington.

The rate of destruction of the Amazon between 1995 and 2000 returned to the same levels as between 1970 and 1980, at 1.9 million hectares (4.7 million acres) -- seven football fields per minute -- according to a study of satellite photographs and Brazil's national Amazon Research Institute.

In 2001, deforestation fell 3.4 percent, when 1.57 million hectares (3.9 million acres) were destroyed, compared with 1.82 million hectares (4.5 million acres) in 2000.

The surveillance system also permits better surveillance on the borders with Suriname, Guyana, French Guiana, Venezuela, Peru, Bolivia as well as Colombia, which has been fighting rebels of the revolutionary armed forces of Colombia (FARC) for four decades.

Besides the surveillance system's command post in Brasilia, three sub-command centers are located in Manaus in the north, Belem in the northeast and Porto Velho to the west.