Outdated charts may have been partially at fault in the undersea grounding of a U.S. nuclear submarine last weekend, according to an agency that analyzes satellite imagery and produces maps for the Defense Department.
Officials at the National Geospatial-Intelligence Agency in Bethesda said yesterday the main chart likely used by the USS San Francisco did not reveal any obstacle anywhere near the boat on the floor of the Pacific last Saturday about 350 miles south of Guam.
The closest notation on the map indicates discolored water about three miles from the accident site. The discolored water was reported by the Japanese most likely in the 1960s or even earlier, according to David Burpee, the agency's spokesman.
The Defense Mapping Agency created the chart in 1989, and it was never revised. That agency later became a part of the National Geospatial-Intelligence Agency, responsible for maps and sea charts.
Burpee said a satellite photograph taken 10 years later could be read in hindsight to show an undersea mountain not on the chart, but that was not clear at the time; in any case, the photo was just one among thousands of shots of ocean expanses that have not been fully charted using the latest methods.
"The charts used today may not reflect the reality of what's actually on the ocean floor," said Burpee, adding that the charts were created with earlier technology.
"You think [the charts] are right until somebody tells you they're not," he said, adding that ships use sonar to pick up ocean forms and pass the information on to the agency.
The Navy has said an initial investigation found the submarine struck a large rock, land or other natural feature and nothing else.
One sailor was killed and at least 23 suffered injuries including broken bones, cuts and bruises. The submarine has a crew of 137.
Burpee said the images taken of the area by a Landsat satellite in 1999 could be viewed on close examination after the accident as indicating a submerged structure, such as a reef or a ridge, but also could be read as showing variations in water color caused by dense growth of plankton or something dumped from a passing ship, such as oil.
"The chart is an imprecise mapping of the bottom to begin with," he said. "There hasn't been a formal hydrographic sweep through that area of the ocean's bottom."
Burpee said there are 150 ships in the world capable of doing that kind of thorough deep water work, and it would take all of them 30 years to map the world's deep water.
"It's not like there was one little area that got away from us, that escaped detection," he said. "This is part of a massive amount of sea that has not been mapped or charted in detail."
The emphasis in charting has been on the Northern Hemisphere because that is where the majority of commerce is, he said.
The San Francisco's nuclear reactor was undamaged, and the submarine made its way to its home port in Guam under its own power. Its outer hull was damaged, but its inner hull remained intact.