Cloud slicing retrievals of the methane concentration in the planetary boundary layer from CHARM-F XCH4 measurements over the Northern Scandinavian wetlands

Kurzfassung

Airborne or spaceborne Integral Path Differential Absorption (IPDA) lidar has the potential to deliver the highly accurate column measurements of trace gases that are needed to reduce the uncertainties on the surface fluxes of anthropogenic greenhouse gases. Among its advantages over passive remote sensing is the very narrow field of view, which makes it possible to exploit “cloud holes” at all spatial scales to increase the coverage. Moreover, in a broken cloud field scenario, it is possible to turn the IPDA lidar into a pseudo-range-resolved lidar and retrieve the average trace gas concentration in the atmospheric layer below the clouds by combining partial columns down to the cloud tops and total columns down to the ground. This is usually referred to as "cloud slicing". Here we report on an attempt to apply cloud slicing on methane data from DLR's airborne IPDA lidar, CHARM-F. The data was acquired on the 23rd of August 2021 over the northern Scandinavian wetlands in the frame of the MAGIC 2021 campaign. We show that cloud slicing enables to overcome some issues with the instrument’s performance during the campaign and that the retrieved methane concentration in the boundary layer matches well with vertical in-situ profiles acquired during the same flight.