The new lidar MERLIN mission for atmospheric methane: Payload and Performance Monitoring

After water vapor and carbon dioxide, methane is the most abundant greenhouse gas in the Earth's atmosphere. The new generation space borne Lidar mission MERLIN (Methane Remote Sensing Lidar Mission) will make very sensitive measurements of the methane distribution with unprecedented quality, i.e. 50km averaged methane columns with a precision of < 2%. After its launch, MERLIN will track down methane sources and sinks on a global scale. The instrument will be mounted on a satellite platform flying at ~500 km altitude in a Sun synchronous orbit. The instrument will continuously send and receive a pair of pulses at two different wavelengths. One wavelength λon is centered on CH4 (methane) absorption line. The second pulse is a reference at λoff which is slightly shifted by a few tenths of nm. It is located where CH4 absorption is relatively smaller, but yet it is close enough to have a nearly identical interaction with the atmosphere and the reflecting surface. From the back-scattered signals of both pulses (on and off), the DAOD (Differential Absorption Optical Depth) of methane is measured, and thus its column density. We will present our approach and strategy to perform a key ground segment work component that supports MERLIN scientific activities which is the long-term monitoring of the Lidar instrument and its measurements. This function includes tracking the behavior of the instrument and its subsystems over time as well as verification and validation of the scientific data during the entire lifetime of the mission. It mainly monitors the instrument’s performance in response to expected or unexpected natural events or technical situations. These are achieved by analyzing the measurement data and housekeeping information over different time frames. We will additionally show how our expertise in SCIAMACHY can be applied to MERLIN