Error Budget of the MEthane Remote LIdar missioN and Its Impact on the Uncertainties of the Global Methane Budget

MEthane Remote LIdar missioN ( MERLIN) is a German-French space mission, scheduled for launch in 2024 and built around an innovative light detecting and ranging instrument that will retrieve methane atmospheric weighted columns. MERLINproducts will be assimilated into chemistry transport models to infer methane emissionsand sinks. Here the expected performance of MERLINto reduce uncertainties on methane emissionsis estimated. A first complete error budget of the mission is proposed based on an analysis of the plausible causes of random and systematic errors. Systematic errorsare spatially and temporally distributed on geophysical variables and then aggregated into an ensemble of 32 scenarios. Observing System SimulationExperiments are conducted, originally carrying both random and systematicerrors. Although relatively small (±2.9 ppb), systemati c errors are found to have a larger influence on MERLINperformances than random errors. The expected global mean uncertainty reduction on methane emissionscompared to the prior knowledge is found to be 32%, limited by the impact of systemati c errors. The uncertainty reduction over land reaches 60% when the largest desert regions are removed. At the latitudinal scale, the largest uncertainty reductions are achieved for temperate regions (84%) and then tropics (56%) and high latitudes (53%). Similar Observing System SimulationExperiments based on error scenarios for Greenhouse Gases Observing SATellite reveal that MERLINshould perform better than Greenhouse Gases Observing SATellite for most continental regions. The integration of error scenarios for MERLINin another inversion systemsuggests similar results, albeit more optimistic in terms of uncertainty reduction.