# MERLIN: A French-German Space Lidar Mission Dedicated to Atmospheric Methane
## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Parameter/Information** & **MERLIN** & **SCIAMACHY** & **COSAT** & **COSAT-2** & \multicolumn{2}{c}{**Seminal SP**} & \multicolumn{1}{c}{**Sentinel 5**} & \multicolumn{1}{c}{**LASI**} & \multicolumn{1}{c}{**goCARB**} & \multicolumn{1}{c}{**LASI-NG**} \\ \hline Agencies & DLR/CNES & DLR/NSO/ESA & JAXA & JAXA & ESA/NSO & ESA & CNES/EUMETSAT & NASA & CNES/EUMETSAT \\ \hline Orbit & Low sun & Low sun & Low sun & Low sun & Low sun & Low sun & Low sun & Low sun synchronous & Geo-stationary & Low sun synchronous \\  & synchroques & synchroques & synchroques & synchroques & synchroques & synchroques & synchroques & & & & synchronous \\ \hline Meas. tech. & Active Lidar & Passive SWIR & Passive SWIR & Passive SWIR & Passive SWIR & Passive SWIR & Passive SWIR & Passive SWIR & Passive SWIR & Passive SWIR \\ \hline Mission status & Selected and & & & & & & & & & & & \\  & funded & Terminated 2012 & In orbit & Selected and & Selected and & Selected and & Selected and & & & & & \\  & funded & functioning & funded & funded & funded & funded & funded & funded & funded & funded \\ \hline Spectrict window (jun) * & 1.64555 & 1.63-1.70 & 1.63-1.70 & 1.63-1.70 & 2.31-2.39 & 1.63-15.0 & 3.62-15.50 & 2.3-2.34 & 3.62-15.50 \\  & 1.64585 * & 2.23-24 & 1.63-1.70 & 2.33-2.38 & 2.31-2.39 & 2.31-2.39 & 3.62-15.0 & 2021/28/35 \\ Launch date & 2021/22 & 2002 & 2009 & 2018 & 2017 & 2022 & 2006/13/18 & 2022/23 & (Metep-GC-1) \\  & & & & & & & & & & \\  & & & & & & & & & \\ \hline Product & XCH\({}_{4}\) & XCH\({}_{4}\) XCO\({}_{5}\), SE & XCH\({}_{4}\) XCO\({}_{5}\) & XCH\({}_{4}\) XCH\({}_{5}\), SE other & XCH\({}_{4}\) XIF, other & Free trop. XCH\({}_{4}\) & XCH\({}_{4}\) XCO\({}_{5}\) & free trop. XCH\({}_{4}\) & XCH\({}_{4}\) XCO\({}_{5}\) & free trop. XCH\({}_{4}\) \\  & other next. gases & & SF & & & & & & & \\ \hline Revisiting time (days) & 28 & 6 & 3 & 6 & 1 & 1 & 1 & 2-8 h * & 1 \\ \hline Smallest spot size (km) & \(0.15\times 0.15\) & \(30\times 6\) & Circular & Circular & \(7\times 7\) & \(7\times 7\) & \(12\times 12\) & \(4\times 5^{d}\) & \(12\times 12\) \\  & & & & & & & & & \\ \hline Sounding/s & 20 & 3 & 0.25 & 0.25 & 215 & 215 & 215 & -250 & 215 \\ \hline Overpass time (local) & 0(\(\times 0\))/18.00 & 10.00 & 13.00 & 13.00 & 13.00 & 13.00 & 9.30 & 09:30/21:30 & Continuous & 09:30/21:30 \\ \hline References & This paper & [2;72] & [73] & [50] & [74] & [75] & [64] & [76] & [52] \\ \hline \hline \end{tabular}  
* Only windows for CF\({}_{4}\) detection are listed
* At continental scale
* Resolution at roughly 30
* The resolution is degraded when latitude increases. German Space Agency (DLR) French Space Agency (CNES); SC-Canning Imaging Absorption SpectroMeter for Atmospheric CHartography) (SCIMACHY); Greenhouse Gases Observing SATellite (GOSTA); shortwave infrared absorption spectrometry (SWIR); Netherlands Space Office (NSO); European Space Agency (ESA); Japan Aerospace Exploration Agency (JAXA); thermal infrared (TR); Teysospheric Monitoring Instrument (TROPMI); solar-induced chlorophyll fluorescence (SIP); National Aeronautics and Space Administration (NASA); European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT); geostomary carbon cycle observatory (goCARB); new generation of infrared atmospheric sounding interferometry (LASI-NG).  
\end{table} 
Table 1: Comparison of MEhane Remote sensing Lidar missioN (MERLIN) mission with other past, current, decided, or proposed missions measuring methane with characteristics that are suitable for source estimation.