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Validation Issues of a Space-based Methane Lidar

Kiemle, Christoph and Fix, Andreas and Ehret, Gerhard and Flamant, Pierre (2014) Validation Issues of a Space-based Methane Lidar. In: AGU Fall Meeting. AGU, 15.-19.12.14, San Francisco.

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Space-based lidar missions targeting greenhouse gases are expected to close observational gaps, e.g., over subarctic permafrost and tropical wetlands, where in-situ and passive remote sensing techniques have difficulties. In the frame of a joint climate monitoring initiative, a “Methane Remote Lidar Mission” (MERLIN) was proposed by the German and French space agencies DLR and CNES. MERLIN is now in Phase B, in which all mission components are planned in detail. Launch is foreseen in 2019. The instrument is an integrated path differential absorption (IPDA) lidar which, installed on a low earth orbit platform provided by CNES, uses the surface backscatter to measure the atmospheric methane column. The globally observed concentration gradients will primarily help inverse numerical models to better infer regional methane fluxes. The lidar signals are able to travel through optically thin cloud and aerosol layers without producing a bias, and MERLIN’s small field of view, of order 100 m, is expected to provide observations in broken cloud environments, often encountered in the tropics. As IPDA is a novel technique, calibration and validation will be essential. It is foreseen to validate MERLIN by under-flying the satellite with another IPDA lidar, CHARM-F, and a passive remote sensor, both airborne. However, active and passive remote sensors have different, pressure and temperature dependent measurements sensitivities (weighting functions), different fields of view, and do not sample the total methane column on-board an aircraft. Furthermore, since the methane profile is not constant, its column depends on the height of the boundary layer and of the tropopause. We investigate the impact of these issues on the expected validation accuracy, and we examine whether the ground-based Total Carbon Column Observing Network (TCCON) may be useful for validation, too. Finally, validation opportunities are dependent on the location and size of cloud-free regions, since clouds with optical thickness > 1 hinder MERLIN observations. Therefore, existing space lidar measurements from the NASA CALIPSO mission with similar field of view were analysed and show that the northern and southern hemisphere’s subtropics are most favourable validation regions.

Item URL in elib:https://elib.dlr.de/91819/
Document Type:Conference or Workshop Item (Speech)
Title:Validation Issues of a Space-based Methane Lidar
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Flamant, PierreÉcole Polytechnique, Palaiseau, FUNSPECIFIED
Date:18 December 2014
Journal or Publication Title:AGU Fall Meeting
Refereed publication:No
Open Access:No
Gold Open Access:No
In ISI Web of Science:No
Keywords:Methane Lidar, MERLIN mission
Event Title:AGU
Event Location:San Francisco
Event Type:international Conference
Event Dates:15.-19.12.14
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Erdbeobachtung
DLR - Research theme (Project):R - Vorhaben LIDAR-Forschung und -Entwicklung
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Lidar
Deposited By: Kiemle, Dr.rer.nat. Christoph
Deposited On:12 Nov 2014 09:33
Last Modified:12 Nov 2014 09:33

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