PINGING THE WIND
Spend enough time sailing and scouring weather forecasts, and odds are good that you’ll occasionally find a day (or three) that doesn’t quite stack up to expectations. Granted, we modern sailors enjoy incredibly high-resolution weather forecasts compared to all historical methods, but in an age of instant access to high-quality information, imprecision can be frustrating. Fortunately, the European Space Agency’s new Aeolus (after the Greek “keeper of the winds”) wind-sensing satellite, which was launched atop a Vega rocket from a site in French Guiana on August 22, 2018, aims to improve forecast accuracy by using sophisticated instrumentation to pipe down observations from sections of the planet that are not otherwise covered by the piecemeal Global Observing System, which is composed of surfaceand space-based subsystems (e.g., satellites, buoys, weather ships, ground stations and weather-radar installations) but lacks sufficient observations from the upper troposphere and lower stratosphere, as well as the tropics and wide swaths of the ocean.
The ESA’S new Aeolus satellite features an Atmospheric Laser Doppler Instrument (“Aladin,” for short) that serves as a kind of Doppler-enabled lidar (read: light and detection ranging technology that floods a targeted area with pulsed laser light and measures the
reflected backscatter with a special sensor). While there’s plenty of complicated engineering involved, Aladin is essentially made up of a powerful laser (technically, multiple lasers and amplifiers), a powerful telescope (pointed at a 35-degree angle away from Aeolus’ orbiting plane) that sports an almost 5-foot (1.5 meter) diameter, and a receiver.
To operate, Aladin fires short, powerful pulses of ultraviolet light down at Earth, which disperse as they hit atmospheric particles, such as gas, dust and water, which are in turn carried by the prevailing wind. Aladin then uses its onboard telescope and receiver to measure the backscattered light reflections, whose wavelengths have shifted, slightly, thanks to the wind’s action. The instrument then uses its Doppler capabilities to determine the time between when the light pulse was fired and when the backscatter returned, and it uses two optical sensors (one senses for molecules, and the other looks for aerosols or water droplets) to measure the Doppler shift to determine the wind’s direction and velocity (Aladin’s maximum vertical coverage extends from Earth’s surface up roughly 19 miles). Finally, Aladin uses its finely tuned photo detectors to change light signals into electronic ones, and it can produce up to 100 wind profiles per hour.
While this certainly sounds like a lot of impressive scientific capability, and while there’s no question that Aeolus will help fill an important gap in the current Global Observing System, it’s important to remember that Aeolus is a single orbiting satellite, meaning that it can only look at a certain portion of the globe at any one time. “The Aeolus satellite is not a ‘silver bullet.’ It will be helpful, but the net effect on forecasts has yet to be proven,” says Predictwind’s Nick Olson, who explained that the New Zealand-based forecasting company pays the European Centre for Medium-range Weather Forecasts a hefty annual fee and therefore will have full access to (and benefit from) Aeolus’ data. “It will be great to see how this data does actually impact [our] forecasts. Hopefully, it is positive and will lead to more satellites in the future. So far as sailors go, this is just going to be another tiny piece of the puzzle slotting into place.”
Crews clean the Aeolus satellite to make sure it’s free of dust particles. A Vega rocket (opposite) brought the satellite to orbit.