Less than a week after the last drops of Hurricane Harvey fell, Houston is just beginning to assess the damage. At least 46 people have died. More than 30,000 houses are flooded and as many as a million vehicles waterlogged. Early estimates suggest the hurricane has inflicted $120 billion in damage on the region, making it the most expensive natural disaster in the country’s history.

“This is going to be a massive, massive cleanup process,” Texas governor Greg Abbott told ABC’s Good Morning America on Friday. “This is going to be a multiyear project for Texas to be able to dig out of this catastrophe.”

Which means the drones’ work has just begun. Responding to the disaster provides a major test—and opportunity—for the country’s fast-growing network of professional UAV operators, almost exactly one year after the Federal Aviation Administration began to hand out licenses for commercial drone operation. (There are at least 2,000 licensed pilots in the Houston area alone, and some 20,300 nationwide.)

“This is the one of the first big disasters where we can show how valuable drones can be,” says Brandon Stark, who directs the Center of Excellence on Unmanned Aircraft System Safety at the University of California, Merced. In the coming weeks and months, they'll help locals assess damage to homes, roads, bridges, power lines, oil and gas facilities, and office buildings—and determine whether it's safe to go back.

Swoop and Assess

As Harvey approached, the FAA did what it usually does in emergencies: It restricted air space in the affected region. That means commercial and private aircraft, including professionally operated drones, are banned from the area until the government says otherwise. “Unauthorized drone operators may prevent the response and recovery aircraft from safely doing their jobs,” says Laura Brown, an FAA spokesperson.

But the FAA has found exceptions to its rule, issuing at least 43 unmanned aircraft system authorizations for groups involved in response and recovery efforts. These waivers let specially sanctioned operators fly in the otherwise verboten airspace, but operators still have to follow the basic regulations for small drones: flying below 400 feet and within the pilot's line of sight, and not over large crowds of people.

Oil and gas companies have claimed five of those authorizations, which they’ve used to inspect their facilities, power lines, and fuel tanks. Union Pacific Railroad grabbed eight, and has had three certified operators flying DJI Mavic Pro drones in the area since Tuesday, inspecting flooded and hard-to-reach areas, like rail yards. Meanwhile, their operations team back at HQ inspects the conditions through a live feed. “This is especially useful for bridge examinations looking for track washouts and other structural changes,” says Raquel Espinoza, a Union Pacific spokesperson.

Pilots working for Fort Bend County, to the southwest of Houston, have used drones to assess damage to roads, bridges, and water treatment plants—and posted the footage online. Other local governments and agencies, including fire departments and state environmental quality officials, have worked with drone operators to identify flooding and drainage problems.

Parker Gyokeres, a New York-based drone pilot, arrived to volunteer in the Houston area on Sunday afternoon, as floodwaters rose. “We probably shouldn’t have done it—it was really stupid—but it was the right thing to do,” he says. He’s now part of an eight-person team of professional pilots and mappers who are working with local government agencies and the Red Cross to assess the damage and work out how to respond. (They have received special authorizations from the FAA for humanitarian operations, and will not be conducting commercial work in the area, Gyokeres says.)