A laser device to measure wind holds promise

FORT STORY

"Who has seen the wind?" poet Christina Rossetti asked in 1893, then answered herself: "Neither you nor I."

My, how times change.

At the edge of the Atlantic Ocean, a steady breeze flapped Grady Koch's pant legs. It caught at the door of a white trailer bearing the NASA logo and the word "VALIDAR."

"I guarantee you, it's even windier out there," Koch said, looking across the gray ocean.

To find out how much windier - exactly and precisely how windy - the engineer from Langley Research Center was testing a new laser instrument he had perched on a bluff at Fort Story.

He retreated inside the trailer to a bank of computer screens, where a series of graphs and images proved the poet wrong.

Who has seen the wind?

Koch has.

VALIDAR sits inside a white room that occupies more than half the trailer. The name is short for "validation lidar," which means it's a test model for a new type of lidar, which is itself short for "light detection and ranging."

What VALIDAR does is shoot pulses of an invisible, infrared laser beam out over the ocean, as far as 10 miles. It doesn't hurt anyone's eyes.

The beam bounces off dust particles being carried by the wind and comes back to the trailer, where some calculations involving the speed of light and the timing of the pulses reveal exact measurements of how fast those particles of dust are moving at a particular height or distance.

"By using this technology you can sit at one location and measure the wind at another location," Koch said. "This hasn't been done before."

VALIDAR has been 20 years in the making. Testing it requires a lot of measurements, and NASA figures they might as well be useful. In 2010, the VALIDAR test unit flew on airplanes to measure wind speeds in hurricanes. This year, the data gathered at Fort Story will go to the Virginia Coastal Energy Research Consortium and to universities that are looking at offshore wind farming.

"It's known the winds are really good," Koch said. "They're quite strong and they're steady."

But the wind speed at turbine height can be dramatically different from the speed at the surface. Because most wind measurements now are taken by balloons (the closest balloon launch site to Hampton Roads is Wallops Island on the Eastern Shore) or by instruments on top of towers, offshore winds are not sampled directly.

VALIDAR could change that.

Eventually, versions of this new lidar on satellites and airplanes could improve weather forecasting, climate modeling, homeland security and military applications such as artillery targeting and helicopter landing.

Koch looked down at VALIDAR, which appeared to be doing nothing.

"It actually looks kind of dull," he said. "You expect flashing beams. It is a laser, which gives some people images of death rays, but it's not."

VALIDAR is circular with a slight dome in R2D2 blue. It is draped in mylar this day, although sometimes it has a hard casing. The laser shoots out the bottom, hits a mirror and bounces upward to the scanner that pokes out of the roof to steer the beam.

When Koch goes in the room to visit VALIDAR, he wears operating room-style paper booties over his shoes.

"Got a whole bag of them," he said. "I go through them like M&Ms."

A sticky mat by the door traps dust that might be picked up on the bootie soles in the three or four steps from desk chair to threshold.

Dust is the enemy of optics.

From his pocket Koch pulled what appeared to be a glass rod about 3 inches long, wrapped in optical tissue. Made of the rare-earth element holmium inside a type of crystal, the rod is the heart of VALIDAR.

"This is unique," Koch said. "This is the only one."

That's because VALIDAR is based on what Koch describes as Ho:Tm:LuLiF, which he pronounces as one word, and then obligingly writes down to make clear the gee-whiz factor.

"Ho" is holmium and "Tm" is thulium, both rare-earth elements that generate an infrared wavelength. LuLiF stands for lutetium lithium fluoride, a host material that allows the laser to produce higher energy levels than previous lidars.

To replicate VALIDAR right now would cost about $2 million, he said. The wind measurements are worth more than that.

"The whole wind farm concept is measured in billions," he said. "Before people make that investment, they want to know what they're going to get out of it."

Koch tested the lidar setup for several weeks this fall in the trailer that would have had a spectacular view of the ocean, if only it had had windows, which, alas, it did not. Still, he enjoyed his perch by the ocean and the dolphins he glimpsed when he happened to go outdoors.

Mostly, he enjoyed tweaking VALIDAR.

"I like this work. I write scientific papers that maybe 10 people in the world read, and nobody cares. This is different. People really want this data, for a lot of reasons."

With VALIDAR on an airplane or satellite, wind observations could be made across the entire globe, Koch said, including the 70 percent that is water. Artillery aiming could become more accurate and long-range weather forecasting more predictable, power generation less polluting and shipboard helicopter landings less dangerous.

Fort Story measures the wind the old-fashioned way, with an anemometer on top of a pole, spinning in the breeze near the two Cape Henry lighthouses, built in 1792 and 1881. VALIDAR hunched quietly nearby, laser beam at the ready.

The unit could go nearly anywhere, Koch said.

"Put it in the lighthouse," suggested a visiting public affairs officer for Fort Story.

"You know," Koch said, "that has a sort of poetic appeal to me."

Diane Tennant, (757) 446-2478, diane.tennant@pilotonline.com