MERLIN: A French-German Space Lidar Mission Dedicated to Atmospheric Methane

The MEthaneRemote sensing Lidar missioN ( MERLIN) aims at demonstrating the spaceborne active measurement of atmospheric methane, a potent greenhouse gas, based on an Integrated Path Differential Absorption (IPDA) nadir-viewing LIght Detecting and Ranging (Lidar) instrument. MERLINis a joint French and German space mission, with a launch currently scheduled for the timeframe 2021/22. The German Space Agency (DLR) is responsible for the payload, while the platform (MYRIADE Evolutions product line) is developed by the French Space Agency (CNES). The main scientific objective of MERLINis the delivery of weighted atmospheric columns of methanedry-air mole fractions for all latitudes throughout the year with systematic errors small enough (<3.7 ppb) to significantly improve our knowledge of methanesources from global to regional scales, with emphasis on poorly accessible regions in the tropics and at high latitudes. This paper presents the MERLINobjectives, describes the methodology and the main characteristics of the payloadand of the platform, and proposes a first assessment of the error budget and its translation into expected uncertainty reduction of methanesurface emissions.