Aeolus, or, in full, Atmospheric Dynamics Mission-Aeolus (ADM-Aeolus), was an

Earth observation satellite An Earth observation satellite or Earth remote sensing satellite is a satellite used or designed for Earth observation (EO) from orbit, including spy satellites and similar ones intended for non-military uses such as environmental monitoring, me ...

operated by the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

(ESA). It was built by

Airbus Defence and Space Airbus Defence and Space is a division of Airbus SE. Formed in 2014 in the restructuring of European Aeronautic Defence and Space (EADS), Airbus SE comprises the former Airbus Military, Astrium, and divisions. Contributing 21% of Airbus reven ...

, launched on 22 August 2018, and operated until it was deorbited and re-entered the atmosphere over Antarctica on 28 July 2023. ADM-Aeolus was the first satellite with equipment capable of performing global

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

-component-profile observation and provided much-needed information to improve

weather forecasting Weather forecasting or weather prediction is the application of science and technology forecasting, to predict the conditions of the Earth's atmosphere, atmosphere for a given location and time. People have attempted to predict the weather info ...

. Aeolus was 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 Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, from the surface of the planet and into the

stratosphere The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher ...

30 km high. The satellite was named after

Aeolus In Greek mythology, Aiolos, transcribed as Aeolus (; ; ) refers to three characters. These three are often difficult to tell apart, and even the ancient mythographers appear to have been perplexed about which Aeolus was which. Diodorus Siculus m ...

, a god from the

Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...

, 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 was planned to provide 64,000 daily profiles from March or April 2019. Its altitude was a low for enough backscattered light sensibility, inducing a short 3 years life expectancy.

Mission

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

Earth's atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...

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

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

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

global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...

to the effects of

air pollution Air pollution is the presence of substances in the Atmosphere of Earth, air that are harmful to humans, other living beings or the environment. Pollutants can be Gas, gases like Ground-level ozone, ozone or nitrogen oxides or small particles li ...

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

profiles.

Satellite

The spacecraft was built by

. 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 March 1980 as the world's first commercial launch service provider. It operates two launch vehicles: Vega C, a Small-lift launch vehicle, small-lift rocket, and Ariane 6, a Medium-lift launch vehicl ...

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

Scientific payload

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

ALADIN

The ALADIN instrument (Atmospheric Laser Doppler Instrument) was a direct detection ultraviolet laser

lidar Lidar (, also LIDAR, an acronym of "light detection and ranging" or "laser imaging, detection, and ranging") is a method for determining ranging, ranges by targeting an object or a surface with a laser and measuring the time for the reflected li ...

consisting of three major elements: a transmitter, a combined Mie and

Rayleigh Rayleigh may refer to: Science *Rayleigh scattering *Rayleigh–Jeans law *Rayleigh waves *Rayleigh (unit), a unit of photon flux named after the 4th Baron Rayleigh *Rayl, rayl or Rayleigh, two units of specific acoustic impedance and characte ...

backscattering receiver assembly, and a

Cassegrain telescope The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to th ...

with a diameter. The transmitter architecture was based on a 150 mJ pulsed diode-pumped Nd:YAG laser, frequency-tripled to provide 60 millijoules pulses of

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

light at 355 nm. This frequency was chosen because of the increased Rayleigh scattering in the ultraviolet region of the spectrum, and because it was 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 consisted of a Fizeau interferometer with a resolution of 100

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

(equivalent to 18 m/s). The received backscatter signal produces a linear fringe whose position was directly linked to the wind velocity; the wind speed was determined by the fringe centroid position to better than a tenth of the resolution (1.8 m/s). The Rayleigh receiver employed a dual-filter

Fabry–Pérot interferometer In optics, a Fabry–Pérot interferometer (FPI) or etalon is an optical cavity made from two parallel reflecting surfaces (i.e.: thin mirrors). Optical waves can pass through the optical cavity only when they are in resonance with it. It is ...

with a 2 GHz resolution and 5 GHz spacing. It analyzed the wings of the Rayleigh spectrum with a CCD; the etalon was split into two zones, which are imaged separately on the detector. The lidar was aimed 35° from

nadir The nadir 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 direction opposite of the nadir is the zenith. Et ...

and 90° to the satellite track (on the side away from the Sun). The processing of the backscatter signals produced 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 was also attainable; from the data processing, information on other elements like clouds and aerosols could also be extracted. The data was disseminated to the main

centres in near-real time. Development of the ALADIN instrument had 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 federal government of the United States, US federal government responsible for the United States ...

for support; however, NASA had 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, and ...

Rokot Rokot ( meaning ''Rumble'' or ''Boom''), also transliterated Rockot, was a Soviet Union (later 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 ( ...

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

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.

Operations

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

millijoule The joule ( , or ; symbol: J) is the unit of energy in the International System of Units (SI). In terms of SI base units, one joule corresponds to one kilogram- metre squared per second squared One joule is equal to the amount of work done ...

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 and published 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''. In 2010, ''IEEE Spe ...

, 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. The satellite was supported by the Europe-wide collaboration Aeolus DISC (Data, Innovation, and Science Cluster) which aims to improve the quality of the data. Aeolus DISC did fly thousands of kilometers from

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

Cape Verde Cape Verde or Cabo Verde, officially the Republic of Cabo Verde, is an island country and archipelagic state of West Africa in the central Atlantic Ocean, consisting of ten volcanic islands with a combined land area of about . These islands ...

to calibrate and validate the data taken by Aeolus. Aeolus was also supported by the international collaboration JATAC (Joint Aeolus Tropical Atlantic Campaign), which took measurements with ground-based

remote sensing Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring inform ...

instruments, especially

s, drones and

radiosonde A radiosonde is a battery-powered telemetry instrument carried into the atmosphere usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. Modern radiosondes measure or calculat ...

s attached to

weather balloon A weather balloon, also known as a sounding balloon, is a balloon (specifically a type of high-altitude balloon) that carries instruments to the stratosphere to send back information on atmospheric pressure, temperature, humidity and wind spe ...

s. These measurements were used to calibrate and validate the measurements by Aeolus. On 30 April 2023, all nominal operations were concluded in preparation for a series of end-of-life activities. A controlled reentry into the atmosphere was planned. ESOC conducted an 'assisted re-entry', using a mixture of natural air drag and commanded

delta-v Delta-''v'' (also known as "change in velocity"), symbolized as and pronounced , as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such as launching from or l ...

. Aeolus re-entered the atmosphere over Antarctica on 28 July 2023.

Impact

In 2020 it was reported that measurements from Aeolus enabled

ECMWF The European Centre for Medium-Range Weather Forecasts (ECMWF) is an independent intergovernmental organisation supported by most of the nations of Europe. It is based at three sites: Shinfield, Shinfield Park, Reading, Berkshire, Reading, Unite ...

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 the coronavirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic. The symptoms of COVID‑19 can vary but often include fever ...

outbreak. In September 2021, since it was launched three years ago, Aeolus had 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 List of specialized agencies of the United Nations, specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology an ...

's Global Observing System, which is a coordinated system of methods and facilities for making meteorological and environmental observations on a global scale. Aeolus improved short-range

forecasts Forecasting is the process of making predictions based on past and present data. Later these can be compared with what actually happens. For example, a company might estimate their revenue in the next year, then compare it against the actual resu ...

, particularly in the

tropics The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

and at

mid-latitudes The middle latitudes, also called the mid-latitudes (sometimes spelled midlatitudes) or moderate latitudes, are spatial regions on either hemisphere of Earth, located between the Tropic of Cancer (latitude ) and the Arctic Circle () in the nort ...

. It might even improve

hurricane A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its ...

forecasts, especially in the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

and

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

s, where

reconnaissance aircraft A reconnaissance aircraft (colloquially, a spy plane) is a military aircraft designed or adapted to perform aerial reconnaissance with roles including collection of imagery intelligence (including using Aerial photography, photography), signals ...

data are unavailable. Since ECMWF started assimilating Aeolus data in 2020 the satellite became one of the highest impact-per-observation instruments in existence. Aeolus created an economic benefit of €3.5 billion for Europe. Aeolus Mission Manager, Tommaso Parrinello, called Aeolus "one of the most successful missions ever flown by ESA". A follow-up mission, called Aeolus-2, will be launched within a decade after the mission end.

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 Spacecraft which reentered in 2023