Above: From left, Gerard Thuiller of France’s Centre national d’études spatiales; Ian McDade and Gordon Shepherd of York’s Centre for Research in Earth & Space Science; Charley Jackman of NASA; and Roger Colley of the Canadian Space Agency
Gordon Sheppard still remembers the early evening of Sept. 12, 1991, at the Kennedy Space Center in Florida. The director of York’s Centre for Research in Earth & Space Science was there for the launch of the space shuttle Discovery. The craft that delivered the Hubble telescope into space was ready for its 13th flight, this time carrying a device called WINDII (Wind Imaging Interferometer, pronounced as Windy), which Shepherd and his team of York researchers had spent years developing so they could measure winds in the stratosphere.
The specially designed photographic instrument was mounted to a satellite with nine other gadgets, all designed to give researchers detailed information about earth’s upper atmosphere. After a 14-minute delay, Discovery’s crew took off to put the Upper Atmosphere Research Satellite (UARS) in orbit for an 18-month mission that instead lasted 14 years. During its 12 years of service (the instrument was switched off two years ago), WINDII provided scientists with a revolutionary new understanding of the dynamics of our atmosphere.
Right: Ian McDade and Gordon Shepherd
Although he couldn’t know that this was the beginning of an experiment that would run until December 2005, Shepherd was still apprehensive on launch day. “So many things can go wrong during a launch,” he said, recalling the excitement of that first day. “Everything worked perfectly and once it was up there we had to see if the instrument was working. It could have happened that the shutters wouldn’t open and we’d have seen nothing for 14 years.”
But they did open and when he returned to WINDII’s operations room in York’s Petrie Science & Engineering Building, Shepherd saw light from the atmosphere and the images from the wind coming in via a satellite link from the Goddard Space Flight Center in Maryland.
The $40-million Canadian-built instrument was sponsored by the Canadian Space Agency (CSA) and France’s Centre national d’études spatiales. At a special event held held on Dec. 16, 2005, the extraordinary success of the mission was celebrated. The event was sponsored by York and the CSA.
Prior to 1991, the winds of the upper atmosphere were largely unknown territory. The WINDII instrument on the UARS measured winds high in the earth’s upper atmosphere, between the altitudes of 80 and 300 km.
At the gathering of leading space scientists held in the Seymour Schulich Building, Shepherd and his team described how the scientific community’s understanding of the earth’s upper atmosphere has changed over the years.
“Every day, winds routinely reach speeds of over 200 kilometres per hour on either side of the equator – at about 20 degrees north and south latitude – which did surprise us,” said Shepherd. “These intense winds are hurricane speed, however the thin air at high altitudes would make them feel more like a light breeze.”
“We observed and measured the existence of 24-hour tidal waves of winds that originate near the earth’s surface,” said Shepherd. “Unlike the twice-daily ocean tides, these gusty winds are driven by the sun’s heat, not the earth’s gravity.”
WINDII used a technique, conceived by Shepherd and colleagues, called Doppler Michelson Imaging. Due to the complicated process of measuring winds in the upper atmosphere (the satellite was several hundred kilometres above where the winds occur) researchers used light as a kind of remote sensor. They measured “airglow”, a form of light in the visible spectrum which is emitted by oxygen atoms and molecules in the atmosphere during the release of stored chemical energy. In particular, it tracked the movements of the oxygen atoms by measuring shifts in the wavelength of light they emit. Through this technology, scientists were effectively able to “see” the wind.
“It’s difficult for many scientists to accept that events so high up in the atmosphere have an effect on what goes on closer to the earth, but the more we study this, the more we see the links between the regions,” Shepherd said.
Years of effort and engineering went into the creation of the WINDII instrument, the first of its kind to be used in space. The instrument took measurements in two directions, allowing scientist to calculate winds moving north and south as well as east and west. WINDII demonstrated that waves play an important role in the circulation of the upper atmosphere and transport the atomic oxygen over large distances.
And what were Shepherd’s thoughts about the end of this highly successful mission that lasted so much longer than intended? “Wonderful but there’s still much more to do,” said York’s professor emeritus. “We’ve got all of the major things out of the data but there’s still many, many more things to do, so I’m going to keep doing this until I really retire. It’s still exciting day by day. I still have students working on the data, so it’s still as marvellous as it was then.”
Shepherd concluded, “Over the years, these insights have caused meteorologists to view the atmosphere differently and model weather patterns at higher altitudes than had been thought necessary. Looking to the future, the pioneering work of WINDII is the foundation for new missions that will improve our understanding of climate change, help protect the ozone layer, and perhaps produce better weather forecasts.”
The future looks bright for new instrumentation such as SWIFT, which continues the tradition of excellence established by UARS and WINDII. Developed by Shepherd, York Professors William Gault, Jack McConnell and Ian McDade, SWIFT will measure wind and ozone in the stratosphere between 15 and 45 km above the Earth. Once in operation, SWIFT will provide a global picture of stratospheric wind movement.