Washington (CNN) -- U.S. government experts trying to construct a model of radiation plumes emanating from Japan's Fukushima Daiichi power plant are being hampered by a "paucity of good data," a senior administration official told CNN.
"We have done some (computer) modeling," the official said, noting the government "got a little bit of data" when helicopters from the USS Ronald Reagan encountered low levels of radiation during flights in the area. But information has been scant, the official said, adding, "Garbage in, garbage out."
The official spoke on background because he was not authorized to speak publicly.
Experts use computer models of plumes to both track radioactivity or other harmful releases and predict their paths. U.S. officials as well as industry officials and critics say radiation from Fukushima Daiichi will not pose a significant health threat to the United States. But plumes could be a factor in causing flight and maritime restrictions.
The official said the United States is sending 39 people and 17,200 pounds of equipment to Japan to assist in efforts to bring the reactors under control. Among the gear is aerial measuring capability to provide radiation readings. He stressed the importance of getting "boots on the ground" to get good data.
From the first hours of the incident, the president's chief Homeland Security adviser, John Brennan, along with personnel from the Department of Energy, the Nuclear Regulatory Commission and other agencies have been maintaining close contacts "as best we could" with people on the ground in Japan, the official said.
Officials have been drawing on a variety of sources for information, including both official and personal contacts in Japan, and open-source material, such as public statements from the Japanese government and Tokyo Electric Power Company web sites. At the Department of Energy, a nuclear incident team has been monitoring developments around the clock, he said.
But data has been hard to come by, and there are "conflicting reports" about damage in some of the reactors, the official said. "There's a lot of genuine confusion about what is going on," he said.
U.S. officials also still do not know what caused the fire in Reactor 4 at the Fukushima Daiichi plant. There is concern that fuel rods in a spent fuel storage pool may have been exposed. That fire reportedly burned for two hours before being extinguished.