Space mission

First light for ICON

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Artist's view of the ICON satellite. The ionosphere emits radiation of different colors that constitute atmospheric luminescence, called airglow. These respective colors reflect changes in the composition of the Earth's ionosphere and the physico-chemical reactions that govern them. Credit: NASA

The ICON satellite, launched last October, has just delivered its first images. Developed by the University of Berkeley for NASA, ICON’s goal is to provide a better understanding of the interactions between the spatial environment and the lower atmosphere. Such interplay constitutes and important source of disturbances in navigation and telecommunication systems. A mission in which researchers from the STAR Institute and the Centre Spatial de Liège are involved.


n Tuesday, December 10, 2019, during the American Geophysical Union's annual meeting in San Francisco, NASA revealed the first images of the Earth's ionosphere taken by the ICON satellite, launched last October. An adventure in which the University of Liège is taking part. Indeed, the Centre Spatial de Liège (CSL) collaborated closely with the University of Berkeley in the design and development of the FUV (Far Ultra Violet) instrument, which was vacuum calibrated in a space environment at the same CSL. The Laboratory of Atmospheric and Planetary Physics (LPAP, STAR Institute / Faculty of Sciences), under supervision of Prof. Denis Grodent, will participate in the analysis of the data sent by the ICON mission, dedicated to the study of the Earth's ionosphere, the region located at the interface between the lower atmosphere and space, at an altitude of 100 to 1000 km.

The ionosphere plays a fundamental role in the propagation of electromagnetic waves, particularly for navigation and telecommunication systems based on links between the ground and one or more satellites. "The density of free electrons in the ionosphere is so large that it disrupts the propagation of signals through it," explains Gilles Wautelet, FRS-FNRS researcher at LPAP.  For example, ionospheric irregularities induce distortion of GPS and Galileo signals, which usually results in an error in the user's position computation or in temporary unavailability of the system." The ICON mission will focus on studying ionospheric variability, which is particularly important in the equatorial region. "It is governed by the activity of the lower atmosphere, such as the presence of hurricanes or storm systems, and by the activity of the sun, which subjects us to a permanent flow of particles called the solar wind. One of the scientific questions to which ICON will attempt to answer is the determination of the respective contribution of these two sources of disturbance," continues the researcher.


First images of the FUV instrument showing the intensity of the airglow as a function of altitude (in the vertical direction). At night, it measures the ionospheric density while daytime observations measure the composition. The purple image shows the emission of nitrogen while the green one, whose maximum intensity is located at altitudes of 200 to 300 km, reflects that of oxygen. Credit: NASA/ICON/Harald Frey/Thomas Bridgman

The first ICON images show light emission profiles of the ionosphere - called "airglow" - in the far ultraviolet observed by the FUV instrument, which allows the terrestrial ionosphere to be imaged both on the edge (the limb) and on the disk. The maximum intensity is observed on the limb at altitudes of about 200 to 300 km, where the ion and electron peak density is generally located. Images reflecting the nitrogen and oxygen airglow (above) are produced every 12 seconds. Such amount of information will allow researchers to accurately measure the finest variations in the composition of the ionosphere.


First images of the MIGHTI instrument, which measures the velocity of oxygen in red and green. The image on the left shows the interferometric fringes that allow accurate wind speed measurement. The image on the right is an airglow picture taken from the International Space Station. The observation of different colors therefore makes it possible to measure the same variable at different altitudes. Credit: NASA/ICON/Christoph Englert/Joy Ng

MIGHTI, another instrument onboard ICON, measures - as an astronaut could do from the international space station - the ionospheric airglow in the visible domain, and in particular in the red and green colors (above). Thanks to an ultra-sensitive system based on the principle of interferometry, MIGHTI will make it possible to measure wind speed in the ionosphere with very high accuracy. "We will compare ICON data with existing terrestrial ionospheric measurements, such as those coming from ionospheric sounders, but also with spatial data, such as GPS measurements, which also allow us to probe the ionosphere with a large accuracy," says Benoît Hubert, FRS-FNRS research associate and Co-Investigator of the FUV instrument. The combination of the different data sources will allow very accurate observations of ionospheric phenomena and thus, in the long term, improve models and forecast. LPAP will also collaborate with the University of California, Berkeley, on data analysis to answer the scientific questions that underlie the ICON project, whose main mission is to better understand the interactions between weather as we know it in the lower atmosphere and weather in space. "Understanding this interaction, called Space Weather, is fundamental to best predict the effects of ionospheric variability on our modern technology," concludes Jean-Claude Gérard, planetary scientist at LPAP and Co-investigator of the FUV instrument.


Dr Gilles WAUTELET  - LPAP I STAR Reseach Institute I Faculty of Science

Dr Benoît HUBERT - LPAP I STAR Reseach Institute I Faculty of Science

Pr Jean-Claude GERARD LPAP I STAR Reseach Institute I FFaculty of Science

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