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Airborne Laser Used to Measure Wind Speed
March 28, 2014

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Over at NASA, a group of scientists continues three decades of work on an instrument they hope one day will orbit Earth, beaming back data that helps meteorologists make better hurricane forecasts.

Meanwhile, power companies are looking to build energy farms off the Virginia and Maryland coasts that would generate enough electricity to light up nearly a million homes.

What’s the connection?

Wind.

NASA is using its Doppler Aerosol Wind (DAWN) instrument to measure wind speed and direction at various altitudes over the Atlantic Ocean. This will help power companies determine where and how to position energy farm wind turbines.

DAWN has been taken on nine flights off Virginia Beach and two off Ocean City, Md., said Grady Koch, a scientist at NASA’s Langley Research Center in Hampton, Va.

“We worked out a way of mapping the wind in three dimensions over the wind energy area,” he said. “I can confirm it’s windy out there – a lot of wind energy.”

Accurately measuring wind is a challenge.

“While wind over offshore oceans is known to be strong and steady, the exact speed and variation isn’t sufficiently understood to assess the economic benefits of offshore wind farming,” Koch said.

“DAWN sends pulses of infrared laser light into the atmosphere, and uses a telescope to collect the small amount of laser light reflected by atmospheric aerosol dust particles. By tracking the motion of these light particles through the air, wind is measured.”

The data, Koch said, will be used several ways.

Companies doing economic analysis of offshore wind farming will use it for cost-benefit studies.

“This economic analysis is a vital part of attracting funds and investment to build the wind farm,” said Koch. “Power output from a turbine is quite sensitive to wind speed, so even small uncertainties in the wind speed can lead to problems in producing an effective cost/benefit study. “

A database of wind speed is needed for such a study, based on meteorological models and observation campaigns using buoys, ships, or towers placed in the ocean. DAWN, Koch said, offers a new technology that can make 3-dimensional maps of the wind vector over the entire wind energy area. The conventional approach measures wind at one or a few isolated locations.

Power companies then take the economic analysis and decide whether or not to proceed. But in moving to the building phase, wind data is needed to determine where to place the turbines. 

“When the wind farm is operational, wind measurements may also be needed to verify that the power output from the individual turbines correlates to the wind speed,” said Koch. “This could be a diagnostic test for the proper operation of all the turbines.”

Finally, turbine manufacturers need to know what range of wind speeds and shear to expect so they can minimize damage potential and maximize the lifetime of the massive machines. Each turbine would be about 450 feet high, with blades 150 feet long.

DAWN of the future

DAWN is the result of 30 years of development. The instrument was used in a 2010 NASA airborne science mission called GRIP (Genesis and Rapid Intensification Processes), a campaign to better understand how tropical storms form and then develop into hurricanes. DAWN was used to measure winds inside many storm systems, including hurricanes Earl and Karl.

“DAWN is the world’s most powerful wind lidar, primarily due to pioneering work performed at NASA Langley on the pulsed 2-micron laser,” said Upendra Singh, principal investigator for NASA’s Laser Risk Reduction Program (LRRP).

“The phrase ‘most powerful’ refers to the combination of three key parameters: laser pulse energy, laser pulse rate, and receiver optical diameter. These three parameters in a pulsed, wind-measuring lidar determine how low the aerosol concentrations can go while still making good wind measurements, Singh said. “Operation to lower concentrations translates to greater atmospheric coverage.”

Most of the funding for DAWN – about $50 million over the years - has been provided by the LRRP, with other follow-on projects supported by the NASA’s Science Mission Directorate and the Earth Science Technology Office in Washington, D.C. said DAWN principal investigator Michael Kavaya.

“Any use of DAWN under different atmospheric conditions and different Earth surface conditions contributes to our understanding of the instrument, and our ability to predict performance in space,” said Kavaya.

The energy-farming project is adding valuable marine wind data to an existing 30-year dataset.

The hope, said Singh, is to provide new data for meteorologists so they can make better forecasts about hurricane intensity, track, and landfall and other normal and extreme weather events. Eventually, scientists hope, a DAWN-like instrument will be launched into orbit to provide continuous global coverage.

“The ultimate goal,” he said, “is to advance laser technology for sustained deployment in space. Space operation will add another societal benefit, improved global weather forecasting.”

NASA monitors Earth's vital signs from land, air and space with a fleet of satellites and ambitious airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the U.S. and around the world that contribute to understanding and protecting our home planet.

For more information about NASA's Earth science activities in 2014, visit:

http://www.nasa.gov/earthrightnow

 

For information on the latest NASA Earth science findings, visit:

http://www.nasa.gov/earth

 

Michael Finneran
NASA Langley Research Center

Charles Bolden and Upendra Singh
NASA Administrator Charles Bolden, on a visit to NASA Langley, listens as Upendra Singh explains how the DAWN instrument works.
Image Credit: 
NASA/David C. Bowman
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Page Last Updated: March 28th, 2014
Page Editor: Joe Atkinson