Alsdorf and his team used four satellites -- three NASA satellites and one from the Japan Aerospace Exploration Agency -- to get the first direct measure of water in the floodplain.
They combined data from the Gravity Recovery and Climate Experiment, the Global Precipitation Climatology Project, the Shuttle Radar Topography Mission, and the Japanese Earth Resources Satellite. They focused on measuring water level changes during the wet and dry seasons between 2003 and 2006.
Taken together, these satellites gave a picture of how the Amazon landscape changed as highland rains surged through the river's many tributaries and the resulting overflow spilled into the lowland jungle. After the water receded, they calculated the change in volume along the floodplain.
These calculations haven't been made before, in part due to the immense difficulty of combining different kinds of data in a reliable way. The researchers had to meld gravity readings -- a measure of the flood water's mass -- with radar and optical measurements of the water level and extent of the floodplain.
The measurements added up to an average of 285 cubic kilometers (285 billion metric tons) of water stored and emptied from the floodplain in a year.
At the height of the rainy season, water flowed into various locations on the Amazon floodplain at a rate of 5,500 cubic meters (5,500 metric tons) per second, and during the dry season, it drained away into the Amazon River -- and, ultimately, into the Atlantic Ocean -- at a rate of 7,500 cubic meters (7,500 metric tons) per second.
The floodplain total, however large, represents only 5 percent of the amount that scientists believe is emptying from the Amazon River into the ocean every year.
