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.)