Abstract
The MEthane Remote 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. MERLIN is 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 MERLIN is the delivery of weighted atmospheric columns of methane dry-air mole fractions for all latitudes throughout the year with systematic errors small enough (<3.7 ppb) to significantly improve our knowledge of methane sources from global to regional scales, with emphasis on poorly accessible regions in the tropics and at high latitudes. This paper presents the MERLIN objectives, describes the methodology and the main characteristics of the payload and of the platform, and proposes a first assessment of the error budget and its translation into expected uncertainty reduction of methane surface emissions.
Highlights
Monitoring methane (CH4) atmospheric concentrations from space is an important but challenging scientific problem.It is important because human-induced emissions and land use changes make the global concentration of CH4 increase and contribute to additional radiative forcing with other increasing greenhouse gases, leading to the rise of the global mean Earth surface temperature [1]
The main scientific objective of MERLIN is to deliver column-weighted dry-air mole fractions of CH4, referred to as XCH4 along the satellite sub-track with a targeted random error better than 27 ppb (Table 3, 50 km averaging along the satellite track, as illustrated in Figure 1) and a systematic error better than 3.7 ppb (68% interval)
The scientific objective is to deliver observations of atmospheric methane from space for all latitudes using a satellite based on an innovative LIght Detecting and Ranging (Lidar) instrument
Summary
Monitoring methane (CH4) atmospheric concentrations from space is an important but challenging scientific problem. NASA plans the geostationary mission geoCARB [51] to be launched after 2020, while CNES and EUMETSAT are preparing the generation of IASI (IASI-NG, 2021) [52] and ESA-EUMETSAT are preparing UVNS/Sentinel 5 (2021) In this context of the evolving development of passive instruments, the MEthane Lidar missioN (MERLIN) proposes an active measurement of XCH4 by employing an IPDA (Integrated Path Differential Absorption) nadir-viewing Lidar instrument [53,54,55,56]. As described below, this new technique has the potential to deliver global coverage during all seasons and with low systematic errors.
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