Satellite-Based Lidar May Help the Weatherman

Lamont Wood

Sending balloons into the upper atmosphere to get weather readings is decades-old technology. A team of researchers is working to improve weather forecasting with the development of a satellite-based laser system for measuring wind speed and direction. It accomplished the first phase of the project seven miles from the summit of Mount Washington, a spot that holds the record for the worst weather in the US, thanks in part to hurricane-force winds.

The Mount Washington Observatory, a nonprofit meteorological and scientific research station; the University of New Hampshire in Durham; Michigan Aerospace Corp. of Ann Arbor, Mich.; and the National Oceanic and Atmospheric Administration worked on the joint project, which involved a specially constructed lidar unit mounted on a reflector telescope. Using a pulsed 5-W green laser, the unit was able to gauge the Doppler shift of the air molecules in the laser beam and calculate wind speed and direction to a distance of 40 km, said Duncan McKee, the observatory's weather education specialist.

A prototype lidar system at the foot of Mount Washington in New Hampshire calculates wind speed and direction within 40 km. Researchers hope to create a network of lidar satellites that will enable them to accurately predict weather up to a week in advance.

The device was mounted at a fixed 45° angle but could sweep the full horizon. It had a resolution of 1 mph and 1° of direction, at 10-ft intervals along the beam. However, the beam could not penetrate clouds, McKee noted.

A second version will be tested within two years in Hawaii, probably using an infrared laser that should penetrate clouds more effectively, he said. A third round of testing will follow in Alaska.

The ultimate goal is a satellite-based system of laser wind gauges, gathering real-time data for every degree of longitude and latitude on the globe.

"That would increase our ability to forecast a great deal, letting us be accurate five to seven days ahead," McKee said. "Now, we can be accurate only about 48 hours out. We are still using 70-year-old technology, sending up two weather balloons a day from various stations to read the upper atmosphere. But that data is hours old when you get it, and we are sending up fewer balloons. So our knowledge of what is going on aloft is sparser."