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 .
Data is scare on radiation coming from Japan 's nuclear reactors . Experts need good practice in building computer models to track radioactivity . Official : ` ` There 's a lot of genuine confusion about what is going on '' Experts say radiation from Japan does not pose a significant health risk to the U.S .