On 17 February 2017, the German Aerospace Center (Deutsches Zentrum für Luft-und Raumfahrt; DLR) Space Administration and Airbus Defence and Space GmbH signed a contract for the design and construction phases of the German-French climate satellite MERLIN (Methane Remote Sensing LIDAR Mission). From 2021, this small satellite mission will measure the methane concentration in Earth's atmosphere to an unprecedented level of accuracy and thus contribute to research into the causes of climate change.
The contract was signed at the Airbus site in Ottobrunn and includes the German contribution to the mission – namely, the development and construction of the methane LIDAR (Light Detection And Ranging), the measuring instrument on board the MERLIN satellite. The core part of the instrument is a laser, which can send out light pulses on two different wavelengths and thus measure the methane concentration at all latitudes with great precision regardless of sunlight.
"Space missions such as MERLIN measure trace gases in our atmosphere and therefore help us to understand the changes that are taking place in our climate; this is an important element towards implementing the United Nations Paris Agreement on Climate Change," said Gerd Gruppe, DLR Executive Board Member responsible for the Space Administration, on the occasion of the contract signing. "Methane is a particularly strong greenhouse gas. Its effect on the climate is 25 times more powerful than that of carbon dioxide (CO2) on a timescale of 100 years. And although the concentration of methane is significantly lower than that of carbon dioxide, at present it contributes to approximately 20 percent of global warming. Effective measures for climate protection must therefore address methane. For that reason, it is necessary to have measurements from all over the world. This can only be achieved with satellites."
Methane is warming up our planet
Methane affects Earth in three different ways: first of all, it has its own global warming potential. In addition, it facilitates the formation of ozone in the lower levels of the atmosphere and also reduces aerosols in the atmosphere. These sulphur aerosols reflect incoming sunlight directly back into space. More methane therefore means less reflection and thus also additional global warming.
Searching using light waves
The LIDAR instrument is being developed and constructed in Germany on behalf of the DLR Space Administration, funded by the Federal Ministry for Economic Affairs and Energy (BMWi). "MERLIN is a great technological challenge. Germany is breaking new technological ground with the innovative laser. We are thus fostering innovation far beyond the boundaries of the project," stressed Gruppe.
The laser is not harmful to the human eye. The wavelengths used fall within the infrared range. These have been chosen so that one of them is absorbed by methane, whereas the other one is not. MERLIN emits two pulses in short succession to the same location on Earth's surface. The reflected light is then picked up and registered by a telescope on the small satellite. One of the pulses is weakened by the methane that is present 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 satellite can also be transmitted to ground stations several times a day.
The LIDAR process has several advantages: the data contain minimal systematic errors. It is therefore possible, using computer models to evaluate the data, to reliably identify sources and sinks of methane and their global distribution. Methane is released in environments where organic matter decomposes where there is little or no oxygen – mainly in the agriculture, forestry, mining and gas extraction industries, as well as in sewage treatment plants and landfill sites. But the largest amount is released as a result of permafrost soil thawing in the Arctic. MERLIN has been designed to track down these sources of methane around the world and make use of any holes in the clouds with its short light pulses. In addition, as an 'active instrument' the LIDAR generates its light itself, the reflection of which it measures. This means that the climate satellite is also capable of monitoring certain regions on Earth – even at night.
German industry participation
The LIDAR instrument is being built by a consortium of companies and research institutes from Germany, France and the Netherlands under the supervision of Airbus Defence and Space GmbH in Ottobrunn. Alongside the design, integration and testing activities for the LIDAR instrument, Airbus is also taking over the construction of several subsystems. The laser, which presents a particular technological challenge, is being constructed by the Fraunhofer Institute for Laser Technology in Aachen in collaboration with Airbus in Ottobrunn. The design is based on the Future Laser (FULAS), developed by the European Space Agency (ESA) and the DLR Space Administration, which was successfully tested in 2016. Other subsystems for the MERLIN LIDAR will come from the German companies SpaceTec GmbH and Hoerner & Sulger GmbH. The telescope mirrors and optics will be supplied by the French company REOSC. The German contribution to the MERLIN ground segment will be provided by SCISYS Deutschland GmbH in close collaboration with the DLR DLR Institute of Atmospheric Physics and the The Remote Sensing Technology Institute (IMF). The MERLIN instrument will be installed on the French satellite bus 'Myriade Evolutions'. The MERLIN climate mission is scheduled to last for three years.