fraction of the scattered ultraviolet photons will reflect back toward a 5-foot (1.5-meter) telescope on the Aeolus satellite.
“Aeolus actually has its own sun on-board in the sense that it’s sending out laser light into the atmosphere, and this laser light is then scattered back from air molecules and particles in the atmosphere,” said Anne Grete Straume, ESA’s Aeolus mission scientist.
The light will return to the Aeolus satellite’s Atmospheric Laser Doppler Instrument — ALADIN — with a slightly different color. By analyzing the change in color caused by the motion of atmospheric air molecules — known as the Doppler effect — scientists can derive wind speeds.
The Doppler effect is the same process that causes an ambulance’s siren to sound different when it approaches and drives away.
“The same happens to the light which is sent out by the satellite,” Straume said in an ESA video interview. “The movement of the air molecules and the particles in its path will actually stretch or compress the light wave, and you get a different color coming back to the instrument.
“We measure the back reflection of the air and the particles at different ranges from the instrument, and from this you can actually measure the winds at different altitudes through the atmosphere from the surface up to the stratosphere,” she said. “About 30 kilometers is the top level that we will be able to measure.”
No other space mission has been able to measure winds at multiple layers of the atmosphere on a global scale. Previous satellites have been limited to deriving winds measurements by tracking the movement of clouds and aerosols, or by measuring the effect of winds on the ocean surface.
But Aeolus will be able to measure wind speeds in clear skies, eliminating the limitations of other missions. Meteorologists currently use weather balloons and airplanes for wind data, but the observations are spotty.
Wind measurements from Aeolus “will fill a significant gap in the wind observing system, particularly in the upper troposphere, the lower stratosphere, in the tropics and over the oceans, where in situ wind observations are lacking,” scientists Michael Rennie and Lars Isaksen from the ECMWF wrote in a blog post earlier this month.
Researchers also intend to analyze data from Aeolus to gain a better understanding of how winds are generated, and how atmospheric currents are linked to changes in Earth’s climate.
“The winds are connecting all the areas together,” Straume said. “It’s transporting air from one place to the next, and it’s also what you feel on the ground, which will actually feed into the storms and the weather.
“There will be scientific users who want to learn more about winds, the relationship between wind, temperature and pressure, and also climate modelists in order to make these long forecasts into the years to come,” Straume said. “They need to understand how the wind is working, and they will pick up our data.
“I’m really looking forward to the first light coming back through the instrument, and being sent down to Earth and analyzed, and we will see what the instrument really can do,” she said. “And I’m looking very much forward to the first wind observations and these bineg used by the weather forecast models.”
As the satellite orbits nearly 200 miles above the Earth, Aeolus will point its ultraviolet laser beam at an angle of 35 degrees to the side of its ground track, in the direction away from the sun.
Aeolus launched into a “dawn-dusk” polar orbit, meaning the spacecraft will roughly follow the boundary between day and night as it travels in a north-south direction, circling the planet every 90 minutes or so.
“We are actually shooting our laser pulse in a slant angle of 35 degrees perpendicular to the orbit, and measuring the line-of-sight return wind speed,” Elfving told Spaceflight Now. “For all purposes, the vertical winds are very small with respect to horizontal winds. So what we’ve promised to give are horizontal line-of-sight winds, which in practice means, more or less, the east-west wind all over the world. That may sound