It's not the CIA or Homeland Security, spying on their neighborhoods. And it's not Google, gathering more images for its controversial Street View website.

The light blue Chevrolet Suburban, covered with graphics, is called a mobile LiDAR vehicle.

Like many other cities, Charleston is under federal and state mandates to map its storm sewers, city storm water manager Tom Elkins said.

But rather than map just the sewers, city leaders decided to map the entire city with LiDAR (Light Detection and Ranging) technology. Though a bit more expensive than the traditional GPS mapping the city first planned to use, LiDAR is many times faster and more accurate.

A consulting firm, Michael Baker Jr. Inc., is using the vehicle to help map the city's storm sewer system.

"We're going to create a full three-dimensional model of the city," said Aaron Morris, a vice president with Baker.

"We will create a system very similar to what Google does with its images, but we take it a step farther with LiDAR," Morris said during a demonstration of the LiDAR truck Wednesday afternoon.

Project Manager Scott Howell pointed out the various instruments mounted on the roof of the truck, starting with twin lasers at the rear corners -- the heart of the system. By aiming a laser beam at a spinning mirror, each unit can capture 200,000 points of information about the surrounding area, up to 200 meters away, every second.

Beside the lasers are two 5 megapixel digital cameras that can shoot pictures at up to three frames per second.

"On top is one of the GPS [global positioning system] units," Howell said. A second GPS unit -- a flattened dome about six inches in diameter -- was mounted on the roof above the driver's seat.

A distance measuring unit attached to the left rear wheel and an inertial measuring unit (IMU) round out the instrumentation. "The IMU measures pitch, roll and yaw," he said, especially handy on rough roads or when the entire instrument deck is removed and mounted on a boat or ATV.

Engineers have used LiDAR for a number of years, most often to map topography from airplanes. "This on-the-ground application is a new technology," Howell said. "This has only been out for two-plus years."

The company used it last year to survey the Nitro-St. Albans bridge for the state Division of Highways, Morris said. "We collected data by driving across the bridge and on a barge underneath it, and used the data to create three-dimensional images of alternate designs."

The plan for Charleston is to drive the LiDAR unit along every city street -- an estimated 345 miles -- at least once in each direction, Howell said. "Depending on the weather, we'll start [today]. If we don't have any delays, it will take five days."

A conventional GPS survey, using technicians with handheld GPS units to record every key location across the city, would take well over a year, he said.

The truck won't dawdle, Morris said. "It goes at the posted speed limit. We can adjust the mirrors to the speed, and that's to avoid interruptions to traffic flow.

"We plan to go out early in the morning, and weekends, when obstructions like parked cars will be minimized. There will be places we can't capture data, because it works on line of sight. We'll come back with a traditional survey crew to fill in the voided areas."

By the end of the survey, the engineers will have compiled what they call a point cloud of data, plus photos, which they'll eventually turn over to the city.

It's a huge amount of information, about 48 megabits for each second the truck is out collecting -- "about 40 floppy discs every second," Morris said.

"Just the cameras by themselves, the photos, we'll have two to three terabytes of data. Altogether, the point cloud plus pictures, 10 terabytes." In the ever-exploding world of computer memory, one terabyte is a thousand gigabytes, or a trillion bytes.

City engineers can extract all kinds of information from the raw data, Morris said, starting with the locations of every surface feature of the storm sewer system. He pointed to a manhole cover at his feet. "We can create an algorithm to search for circular objects.

"If the city needed to know the location of all its traffic signals, they wouldn't have to hire a consultant to do that. They could pull that out. Same thing with street signs, or fire hydrants, or utilities, or pavement conditions."

The survey truck might have to work around an unexpected obstacle or two this week, Morris said: "I'm a little worried about Ringling Brothers parked beside the road. We may have some elephants standing in the way."

Reach Jim Balow at ba...@wvgazette.com or 304-348-5102.