Since the Sept. 11 attacks, about 100 employees of a little-known branch of the Defense Department called the National Geospatial-Intelligence Agency — and some of the country's most sophisticated aerial imaging equipment — have focused on observing what's going on in the United States.
Their work brushes up against the fine line between protecting the public and performing illegal government spying on Americans.
Roughly twice a month, the agency is called upon to help with the security of events inside the United States. Even more routinely, it is asked to help prepare imagery and related information to protect against possible attacks on critical sites.
For instance, the agency has modified basic maps of the nation's capital to highlight the location of hospitals, linking them to data on the number of beds or the burn unit in each. To secure the Ronald Reagan funeral procession, the agency merged aerial photographs and 3D images, allowing security planners to virtually walk, drive or fly through the Simi Valley, Calif., route.
The agency is especially watchful of big events or targets that might attract terrorists — political conventions, for example, or nuclear power plants.
Everyone agrees that the domestic mission of the NGA has increased dramatically in the wake of Sept. 11, even though laws and carefully crafted regulations are in place to prevent government surveillance aimed at Americans.
The agency is not interested in information on U.S. citizens, stresses Americas office director Bert Beaulieu. "We couldn't care less about individuals and people and companies," he said.
But that's not good enough for secrecy expert Steven Aftergood, who oversees a project on government secrecy for the Federation of American Scientists. "What it all boils down to is 'Trust us. Our intentions are good,'" he said.
Adds Marc Rotenberg, executive director of the Electronic Privacy Information Center in Washington: "As a general matter, when there are systems of public surveillance, there needs to be public oversight."
Geospatial intelligence is the science of combining imagery, such as satellite pictures, to physically depict features or activities happening anywhere on the planet.
Outside the United States, it can be a powerful tool for war planners who may use imagery to measure soil wetness to determine if tanks could travel an area. It can help weapons proliferation experts look for ground disturbances that can indicate new underground bunkers.
Before Sept. 11, the NGA's domestic work often meant things like lending a hand during natural disasters by supplying pictures of wildfires and floods.
But now the agency's new Americas Office has been called on to assemble visual information on more than 130 urban areas, among scores of other assignments, including maps of the national mall, the country's high-voltage transmission lines and disaster exercises.
Sometimes, agency officials may cooperate with private groups, such as hotel security offices, to get access to video footage of lobbies and hallways. That footage can then be connected with other types of maps used to secure events — or to take action, if a hostage situation or other catastrophe happens.
The level of detail varies widely, depending on the threat and what the FBI or another agency needs.
"In most cases, it's not intrusive," said the NGA's associate general counsel, Laura Jennings. "It is information to help secure an event and to have people prepared to respond should there be an attack, or to analyze the area where a threat has been made."
According to Executive Order 12333, signed by President Reagan in 1981, members of the U.S. intelligence community can collect, retain and pass along information about U.S. companies or people only in certain cases.
Information that is publicly available or collected with the consent of the individual is fair game, as is information acquired by overhead reconnaissance not directed at specific people or companies.
The NGA says it has aggressive internal oversight and its employees go through annual training on what is and isn't allowed.
"If they deviated from their own rules, how would it be discovered?" asks secrecy expert Aftergood. "I am not satisfied that they have an answer to that question."
One oversight committee in Congress noticed after Sept. 11 that an intelligence agency was snapping pictures of the United States, said a congressional aide, speaking on condition of anonymity. A staff member is now monitoring the issue, and the aide said so far problems have not been spotted.
But Aftergood notes that while intelligence budgets have increased dramatically in the last five years, congressional oversight budgets have not.
Even the agency concedes gray areas do emerge.
Generally, for example, intelligence resources can't be used for law enforcement purposes. So the FBI or another agency could use an NGA-produced aerial photograph to solve a domestic crime. But the NGA couldn't take actions to target a specific individual, such as highlight a suspect's home, unless the information was linked directly to a national security issue.
Agency officials call that "passive assistance" and say certain legal tests must be met.
The NGA says it is working to build trust — with the public and with private companies.
Before Sept. 11, for instance, chemical plants and other critical sites weren't as cooperative as they are today, out of fear that aerial photographs might be shared with federal environmental regulators. NGA officials say the Homeland Security Department has been careful to protect proprietary information.
What if NGA analysts were to see an environmental crime?
"I don't think any of my people know enough to know an environmental crime," Beaulieu said.