On 14 September 2016 in Berlin, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and the French space agency (Centre national d'études spatiales; CNES) signed a cooperation agreement for the design, construction and operational phases of the Franco-German climate satellite MERLIN in the presence of Brigitte Zypries, Parliamentary State Secretary at the German Federal Ministry for Economic Affairs and Energy (BMWi) and Federal Coordinator of German Aerospace Policy, as well as Thierry Mandon, French Minister of State for Higher Education and Research. The agreement was signed by Gerd Gruppe, DLR Executive Board Member responsible for the DLR Space Administration and Jean-Yves Le Gall, the President of CNES. The small satellite mission MERLIN – Methane Remote Sensing LIDAR Mission – will measure the concentration of methane in the Earth's atmosphere with unprecedented accuracy. The mission will last for three years.
"With MERLIN, France and Germany are making a significant contribution to climate change research. Space missions such as MERLIN help us to gain a greater understanding of the mechanisms that influence the Earth's climate. This is therefore also an essential component for implementing the Paris Climate Agreement", stated Brigitte Zypries during the signing ceremony.
"Germany and France will process and evaluate the data from the mission together and in close cooperation with research laboratories. MERLIN will be launched in 2021 and will orbit Earth at an altitude of approximately 500 kilometres," said Thierry Mandon.
MERLIN is based on the new 'Myriade Evolutions' satellite bus, developed by CNES in collaboration with the French aerospace industry. The satellite payload, an active LIDAR (LIght Detection And Ranging) instrument that can conduct measurements even at night and through thin clouds, is being developed and built in Germany on behalf of the DLR Space Administration with funds from the German Federal Ministry for Economic Affairs and Energy. The methane LIDAR has a laser that can emit light at two different wavelengths, and is therefore capable of carrying out extremely precise measurements of methane concentrations at all latitudes, regardless of sunlight.
Methane is a particularly strong greenhouse gas. Its impact on the climate is about 25 times stronger than that of carbon dioxide. Although the concentration of methane is considerably lower than that of carbon dioxide, methane is responsible for approximately 20 percent of today's global warming.
Explaining the importance of the mission, Gerd Gruppe states: "Effective measures for climate protection must address methane. Precise and consistent measurements from all over the world are needed. This can only be achieved with a satellite. With MERLIN, Germany and France are pursuing a common goal. To achieve this, France is contributing the satellite bus and Germany an innovative space laser. Constructing such an instrument is a major technological challenge. We are thus providing innovation to last far beyond the project itself."
The LIDAR instrument on board MERLIN emits light that is not harmful to the human eye. It releases short pulses at two different infrared wavelengths. They have been selected so that one is absorbed by the methane and the other one is not. MERLIN emits these two pulses in quick succession to the same location on Earth's surface. The pulses are reflected and then picked up by the telescope and registered by the small satellite. One of the pulses is weakened by the methane in the atmosphere, the other is not. This difference enables scientists to determine the quantity of methane present between the satellite and the ground. The data acquired by the satellites can also be transmitted to the ground stations several times a day.
"The LIDAR method has scientific advantages: it is a so-called 'self-calibration' procedure, which means that the data contains an extremely low amount of systematic errors. So, when the data is supplied to numerical models for analysis, it is possible to reliably determine the methane sources and sinks, as well as their distribution across the globe," explains DLR Project Manager, Matthias Alpers. With its short light pulses, MERLIN is able to 'take advantage of' every break in the clouds. In terms of a LIDAR, MERLIN is also an 'active' instrument. In other words, it generates the light itself and then measures its reflection. This enables the climate satellite to conduct measurements on Earth at night-time.
The LIDAR will be built by a consortium of companies and research institutions from Germany, France and the Netherlands, under the leadership of Airbus Defence and Space GmbH in Ottobrunn.