Aeolus, or, in full, Atmospheric Dynamics Mission-Aeolus (ADM-Aeolus), is an Earth observation satellite operated by the European Space Agency (ESA). It was built by Airbus Defence and Space and launched on 22 August 2018. ADM-Aeolus is the first satellite with equipment capable of performing global

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...

-component-profile observation and will provide much-needed information to improve

weather forecasting Weather forecasting is the application of science and technology to predict the conditions of the atmosphere for a given location and time. People have attempted to predict the weather informally for millennia and formally since the 19th cent ...

. Aeolus is the first satellite capable of observing what the winds are doing on

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, from the surface of the planet and into the stratosphere 30 km high. The satellite was named after

Aeolus In Greek mythology, Aeolus or Aiolos (; grc, Αἴολος , ) is a name shared by three mythical characters. These three personages are often difficult to tell apart, and even the ancient mythographers appear to have been perplexed about which A ...

, a god from the

Greek mythology A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities ...

, the ruler of the winds.

Program

The program was initially approved in 1999 for a 2007 launch but technological obstacles caused 11 years of delay, as it was launched on 22 August 2018. For an estimated €481 million (US$568 million) program cost, it should provide 64,000 daily profiles from March or April 2019. Its altitude is a low for enough backscattered light sensibility, inducing a short 3 years life expectancy.

Mission

Aeolus is the fifth planned satellite in the Living Planet Programme (LPP) of the European Space Agency (ESA). The main goal of this mission is to further develop the knowledge of

Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...

and

weather system In meteorology, a low-pressure area, low area or low is a region where the atmospheric pressure is lower than that of surrounding locations. Low-pressure areas are commonly associated with inclement weather (such as cloudy, windy, with possible ...

s. By recording and monitoring the weather in different parts of the world, Aeolus will allow scientists to build complex weather models, which can then be used to help predict how that environment will behave in the future. These predictions will be useful in the short-term, since they can be applied to

numerical weather prediction Numerical weather prediction (NWP) uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in th ...

in order to make forecasts more accurate. The mission will thus improve the knowledge of all sorts of weather phenomena, from

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

to the effects of

air pollution Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different typ ...

. Aeolus is seen as a mission that will pave the way for future operational meteorological satellites dedicated to study Earth's

profiles.

Satellite

The spacecraft was built by Airbus Defence and Space. In 2014, the integration of ALADIN instrument was completed and vacuum along with vibration testing begun. On 7 September 2016, ESA and

Arianespace Arianespace SA is a French company founded in 1980 as the world's first commercial launch service provider. It undertakes the operation and marketing of the Ariane programme. The company offers a number of different launch vehicles: the heavy ...

signed a contract to secure the launch of the Aeolus satellite.

Scientific payload

The wind-component profiles will be measured by the Atmospheric LAser Doppler INstrument (ALADIN).

ALADIN

The ALADIN instrument (Atmospheric Laser Doppler Instrument) is a direct detection ultraviolet laser lidar consisting of three major elements: a transmitter, a combined Mie and Rayleigh backscattering receiver assembly, and a Cassegrain telescope with a diameter. The transmitter architecture is based on a 150 mJ pulsed diode-pumped Nd:YAG laser, frequency-tripled to provide 60 millijoules pulses of

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

light at 355 nm. This frequency was chosen because of the increased Rayleigh scattering in the ultraviolet region of the spectrum, and because it is eye-safe at distances greater than several hundred metres.Sandip Pal, Andreas Behrendt, Marcus Radlach, Thorsten Schaberl, and Volker Wulfmeye
Eye-Safe Scanning Aerosol Lidar at 355 nm
/ref> The Mie receiver consists of a

Fizeau interferometer A Fizeau interferometerLawson, Peter R. "Principles of Long Baseline Stellar Interferometry." Course notes from the 1999 Michelson Summer School, held August 15–19, 1999. Edited by Peter R. Lawson. Published by National Aeronautics and Space Admi ...

with a resolution of 100

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

(equivalent to 18 m/s). The received backscatter signal produces a linear fringe whose position is directly linked to the wind velocity; the wind speed is determined by the fringe centroid position to better than a tenth of the resolution (1.8 m/s). The Rayleigh receiver employs a dual-filter Fabry–Pérot interferometer with a 2 GHz resolution and 5 GHz spacing. It analyzes the wings of the Rayleigh spectrum with a CCD; the etalon is split into two zones, which are imaged separately on the detector. The lidar is aimed 35° from

nadir The nadir (, ; ar, نظير, naẓīr, counterpart) is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direc ...

and 90° to the satellite track (on the side away from the Sun). The processing of the backscatter signals will produce line-of-sight wind-component profiles above thick clouds or down to the surface in clear air along the satellite track, every . Wind information in thin cloud or at the tops of thick clouds is also attainable; from the data processing, information on other elements like clouds and aerosols can also be extracted. The data will be disseminated to the main

centres in near-real time. Development of the ALADIN instrument has been problematic. The ultraviolet laser was causing damage to the optical surfaces in a vacuum. ESA scientists asked

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

for support; however, NASA has minimal experience with lidar of this design. Technology required for the satellite was pushing the technology envelope; therefore, after problematic development, ESA asked Airbus to perform additional full-model tests in a vacuum before continuing mission development. Overall complications involved in the instrument caused an estimated 50% final cost overrun, so ESA had to come up with additional funding for the project.

Launch

Aeolus was designed to be compatible with many small-capacity launch vehicles such as

Vega Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, a ...

Rokot Rokot (russian: Рокот meaning ''Rumble'' or ''Boom''), also transliterated Rockot, was a Russian space launch vehicle that was capable of launching a payload of into a Earth orbit with 63° inclination. It was based on the UR-100N (SS- ...

or Dnepr. In November 2013, ESA scheduled the launch on a VEGA in one of the five flights of the VERTA Programme, but in 2015 launch was postponed to August 2018 due to problems with their lidar development. A €32.57 million launch contract with

was signed on 7 September 2016. The launch finally took place on 22 August 2018 on a Vega launch vehicle from French Guiana at 18:20 local time.

Status

The satellite was launched on 22 August 2018. Three months of testing was conducted before including data in weather models. One year of usage has resulted in reduced power from the primary laser. After switching to the second laser, the instrument is meeting mission objectives. In mid-2019, ESA determined that the UV laser was losing power: it started with pulses of 65

millijoule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. ...

s once it reached orbit, but that energy declined 20 to 30% in the first nine months, and was losing one millijoule per week in May 2019. ESA then decided to switch to a backup laser that had not been used, offering the opportunity to complete the expected 3 year life of the satellite. The reportBackup Laser to Revive Aeolus Wind-Sensing Satellite
Jeff Hecht,

IEEE Spectrum ''IEEE Spectrum'' is a magazine edited by the Institute of Electrical and Electronics Engineers. The first issue of ''IEEE Spectrum'' was published in January 1964 as a successor to ''Electrical Engineering''. The magazine contains peer-reviewe ...

, 2019-06-27 also said that the satellite's orbit at 320 km required re-boosting every week, limiting the satellite's life to the available propellant. In 2020 it was reported that measurements from Aeolus enabled ECMWF to partly compensate for reduced measurements from commercial aircraft at the start of the

COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was identified in Wuhan, China, in December 2019. The disease quickly ...

outbreak. In September 2021, since it was launched three years ago, Aeolus has far exceeded expectations and frequently hailed a remarkable success. It was developed as a research mission and to demonstrate how novel laser technology could deliver vertical profiles of Earth's wind. These measurements were much needed, for example by the

World Meteorological Organization The World Meteorological Organization (WMO) is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. The WMO originated from the Intern ...

's Global Observing System, which is a coordinated system of methods and facilities for making meteorological and environmental observations on a global scale. It is expected to reenter the atmosphere in 2022.

References

External links

Aeolus page at Airbus Defence and Space

Aeolus pages at ESA, with latest news

Aeolus blog by Gilles Labruyère, mechanics engineer in the Aeolus project
{{Orbital launches in 2018 Earth observation satellites of the European Space Agency Spacecraft launched in 2018 Spacecraft launched by Vega rockets 2018 in French Guiana