Aeolus, Measurer of the Winds

18 February 2020

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Forecasting the weather just got a little easier, thanks to a new milestone for the European Space Agency’s (ESA) Aeolus satellite mission...

Data gathered by Aeolus, ESA’s wind-measuring satellite, is being incorporated into weather-forecasting models for the first time. “It’s been known for a number of decades that there is a big lack of wind measurements,” says mission scientist Anne Grete Straume from ESA. “That’s where Aeolus comes in, as a totally new mission, giving you constant wind measurements from 30 kilometres all the way down to the [Earth’s] surface in cloud-free areas.”

The satellite’s data is particularly useful for forecasting in the Southern hemisphere and the tropics. Here, the lack of land limits the use of ground-based wind measurement techniques, such as weather balloons. “The Aeolus satellite flies from pole to pole. It gives you much, much better coverage than you get from land,” explains Straume.

And although the sunny isles at the equator may seem far from home, “you need to know what the wind is over the oceans and in the tropics to know what the weather will be in Europe in the coming days, because our weather often travels in from the west.” 

The satellite, the first of its kind, uses a laser to measure the wind on Earth from space. The laser is fired through the atmosphere where it scatters off air molecules. Some of the signal gets reflected back to the satellite, and measurements of how much the returned signal has changed allows the mission team to calculate wind speeds and directions.

This is the Doppler effect, and it's is similar to the changing sound of an ambulance or police siren as the vehicle approaches, passes and then drives away. As it comes towards you, the siren goes up in pitch, and as it retreats, the pitch drops. Sound and light are both waves, so this same effect occurs in the scattered laser signal too. But instead of tracking a change in pitch, the Aeolus scientists track how the colour, or frequency, of the laser light wave has changed.

The satellite was intended as a one-off research mission, but with the impact the data is already having, it’s possible Aeolus may end up with some brothers and sisters. "It’s looking very promising for the future. We hope that the Aeolus technology will be flying for many years to come and give us many, many more observations, which will have an even bigger impact on the forecast," says Straume.

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