Study shows latest gov't spill estimate right

WASHINGTON (AP):

After several missteps, the federal government finally got it right, accurately estimating how much oil spilled into the Gulf of Mexico, an independent scientific study found.

Nearly 185 million gallons of oil spilled from the broken BP well into the Gulf of Mexico this summer, according to a study by two Columbia University researchers who made their estimates based on video of the oil spewing from the well.

The federal government's final estimate was a shade more than 172 million gallons. The Columbia researchers' estimate is 12.6 million gallons more than the federal figure. However, because it is so difficult to get a precise estimate, there is a large margin of error for both the government figure and the Columbia number. The margin is so large that the two estimates essentially overlap, the researchers said. Their study was published online Thursday in the journal Science.

US Geological Survey Director Marcia McNutt, who oversaw federal estimates of the spill size, called the Columbia study "a completely independent and unbiased verification of the government result."

Tim Crone of Columbia, the lead researcher who calculated his estimate based on detailed flow formulas determined by watching video of the leak concurred, "Our numbers overlap, so sure, we agree."

Independent peer review

But Crone said he is more confident in his estimate, because it went through the rigorous independent peer review required to be published in a respected journal. He added that it is hard to compare in depth to federal numbers "because few details of their methods have been released."

Crone used a different technique to study video than most scientists who analyse flow rates from video. Usually, scientists track particles and calculate a speed as they travel across a screen, sort of like watching a car race down a highway. But in this case the particles were hard to track, so Crone used a technique he has been working on for a decade. Crone studies individual points in the video - all the points - and watches their changes in colour and texture. For this study, Crone reviewed video from two dates, May 15 and June 3, and extrapolated for the spill estimate.

The Columbia estimate has a margin of error of 20 per cent, so the spill would be somewhere between 148 million and 222 million gallons. The federal estimate had a 10 per cent margin of error, so the spill would be somewhere between 155 million and 189 million gallons.

Federal estimates of how much oil spilled, and where it has gone, have been criticised by both scientists and Congress because the agencies involved have not provided detailed information on how they calculated their figures. But the government numbers were not based solely on traditional video analysis; they also factored in measurements of pressure and estimates from photos and infrared images taken from airplanes and satellites.

Purdue University engineering professor Steve Wereley, who at first was critical of federal efforts and then joined the government team, said he trusts the government work as more comprehensive than Columbia's.

The federal government struggled mightily to calculate the spill's size at first and was sharply criticised for clinging to a too-low estimate for weeks.

Ian MacDonald, a Florida State University oceanographer, said that by his count it took eight tries for the federal government finally to get its calculations right.