PARIS — Astrium Satellites will build two high-precision spectrometers to monitor the chemical composition of the atmosphere over Europe and North Africa from geostationary orbit under a contract with the European Space Agency (ESA) valued at 149.2 million euros ($209 million), Astrium announced July 11.

The two identical instruments, each weighing about 150 kilograms, will be integrated onto the Meteosat Third Generation satellites now under construction by Thales Alenia Space of France and OHB Technology of Germany under a separate ESA contract.

Astrium Satellites’ Ottobrunn, Germany-based division will provide the two instruments for launches in 2019 and 2027 aboard these spacecraft.

The Meteosat Third Generation satellites are being built for Europe’s weather satellite organization, Eumetsat, but have also been designated as the hosts for the so-called Sentinel-4 mission of environmental surveillance. The two spectrometers will carry out the Sentinel-4 mission.

Sentinel-4 and other Sentinel payloads and dedicated satellites are being built with ESA oversight for the European Union’s executive commission as part of a broader environmental initiative called Global Monitoring for Environment and Security (GMES).

Astrium Satellites Chief Executive Evert Dudok said in a July 11 statement that the Sentinel-4 spectrometers, which will follow on from the Sciamachy instrument on ESA’s Envisat satellite in low Earth orbit, will be built by a team of 45 companies in 11 European nations.