Scientists delighted with first data from wind mission

Aeolus measurement track, with Aladin lidar instrument aimed away from the Sun (ESA/ATG medialab)

12 September 2018

Scientists working on the European Space Agency’s newest mission – the Aeolus wind-monitoring satellite – are encouraged by early data, returned less than a month after launch.

Early on in a commissioning phase expected to last several months, the satellite has delivered data from one orbit, showing “large-scale easterly and westerly winds between the Earth’s surface and the lower stratosphere, including jet streams”; and, adds ESA’s mission scientist Anne Grete Straume, this early data shows the stratospheric polar vortex around the South Pole, which plays a role in ozone layer depletion.

Florence Rabier, director-general of the European Centre for Medium-Range Weather Forecasts, which plotted this first data, said: “The results so far look extremely promising, far better than anyone expected at this early stage.”

This fifth mission in ESA’s Earth Explorers basic science series – following GOCE (mapping Earth’s gravity), SMOS (Soil Moisture and Ocean Salinity), CryoSat (measuring sea ice and ice sheet thickness) and Swarm (Earth’s magnetic field) – is the first satellite to directly measure winds from space, and so should fill gaps in our understanding of global wind patterns to altitudes as high as 30km. Today, winds are measured by weather balloons, tracking cloud movement or observing sea waves to detect surface winds.

Aeolus, named after the ancient Greek “keeper of the winds”, is a one-payload mission, carrying a laser range finder being billed as one of the most sophisticated instruments ever orbited. This Atmospheric Laser Dopler Instrument (Aladin) uses lidar – laser detection and ranging – to detect air molecules or airborne particles and so measure wind direction and speed.

The mission is technically challenging, too, for its engineering. The ultraviolet laser pulses 50 times per second, heating the optics to some 1,700°C and necessitating a complex radiator system on the “dark” side of the satellite’s Sun-synchronous orbit. That orbit maintains a path above either dusk or dawn on the surface, and measurements are taken on the “night” side of the satellite – but Aeolus still flies in Earth’s shadow for some 20 minutes per orbit with the result that temperature variations are large.

And, to fly close to the particles it is trying to measure, Aeolus is in orbit at just 320km, ,where fuel consumption is high to hold station.

So ultimately, Aeolus is a technology demonstrator with a planned mission life of just three years – but high hopes of further missions to follow.

First wind data from Aeolus; westerly winds in blue, easterly in red – polar winds travel in one direction but in this plot change colour because the satellite’s viewing angle changes as it crosses the pole (ESA/ECMWF)