May 6, 2020


The IASI (Infrared Atmospheric Sounding Interferometer) mission led by CNES in partnership with Eumetsat relies on three weather satellites in low Earth orbit: MetOp-A, launched in October 2006, MetOp-B in September 2012 and MetOp-C in November 2018. Each of these satellites is carrying a IASI instrument installed by CNES and built by Thales Alenia Space. Data from the three instruments support weather forecasting and are helping to monitor Earth’s environment and climate.

The IASI instruments’ exceptional features—day/night observation of land surfaces and oceans, spatial coverage and high spectral and radiometric quality of data—combined with the length of the mission have enabled its scope to be extended to studying and monitoring the atmosphere’s chemical composition and climate change. Each instrument provides more than one million measurements per day, used by teams of research scientists and engineers at the LATMOS atmospheres, environments and space observations laboratory belonging to the Institut Pierre Simon Laplace (IPSL) to compile maps of 30 gases. Each gas has its own unique spectral signature, making it possible from the satellite data to obtain atmospheric temperature and humidity characteristics as well as the concentrations of certain chemical species as a function of altitude. IASI is today the global benchmark for hyperspectral sounding of the atmosphere.

The main sources of atmospheric pollution are emissions from road traffic and industrial facilities. While the Copernicus programme’s Sentinel 5-P satellite is observing nitrogen oxide (NO2), IASI is observing carbon monoxide (CO). This colourless and odourless gas persists in the atmosphere for several weeks and is carried by winds over hundreds of kilometres. Maps of carbon monoxide generated from IASI data enable scientists to trace emissions and variations. For example, these data are showing the impact of lockdown measures on CO concentrations in the world’s main population centres, beginning with China, where coal-fired power stations emit a lot of the gas. The effects of the lifting of the lockdown are now also visible there.


In Europe, which burns are lot less coal than China, the decrease is not so pronounced but nonetheless visible in the region around Milan, lying in a depression that acts as a trap for pollutants. IASI observed a drop of around 20 to 30% in CO pollution over the first fortnight of March between 2020 and the average of the previous two years.

© Maya George, LATMOS/Sorbonne Université

IASI also enables monitoring of another polluting gas, ammonia (NH3), which comes chiefly from intensive livestock farming and production of nitrogen fertilizers. For example, despite the sharp drop in road traffic as a result of the lockdown and the associated reduced concentrations of nitrogen oxides (NOx) observed by the AirParif air quality monitoring network, two peaks in particulate emissions were recorded on 20-21 and 27-28 March, correlated to increased amounts of ammonia in the atmosphere. This result confirmed the impact of farming activities in the composition of the air over Paris.

CNES is tasked with monitoring the IASA instruments, providing expertise and assuring the quality of first-level data. It also provides support for data exploitation by research laboratories. CNES and Eumetsat are currently readying a new-generation instrument, IASI-NG, to fly on the future MetOp-SG satellites.

Pascale Bresson    Press Officer    Tel. +33 (0)1 44 76 75 39
Raphaël Sart    Press Officer    Tel. +33 (0)1 44 76 74 51

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