"Field studies show that there are more deforested areas than those seen by satellite, because of cloud cover. There are completely covered area that have not had satellite imagery for four years," one of its members, Paulo Adario, told reporters in Sao Paulo.
Greenpeace said Brazil's government was largely to blame for the stripping of the forest, having fallen short in a preservation program because of "a lack of executive and political coordination."
Brasilia has been cracking down on illegal logging and land-clearing in the Amazon since revealing that its vast forest -- sometimes called the lungs of the Earth for its role in absorbing carbon dioxide -- had lost another 7,000 square kilometers (2,700 square miles) in the last half of 2007.
The government on Wednesday announced it was doubling fines against those found contributing to the deforestation to 5,000 dollars.
Greenpeace called for the measures to go further, including the creation of a landowners' registry in the Amazon to make it easier to determine responsibility for cleared areas.
"Brazil doesn't know who is who, or where people are in the Amazon," another Greenepeace representative, Marcelo Marquesini, said.