WALES, the Airborne Demonstrator for a Water Vapor Differential Absorption LIDAR in Space

Kurzfassung

One of the major challenges in contemporary climate research is to detect seasonal and inter-annual variabilities of water vapor for determining both the sign and the magnitude of its feedback to the Earth’s system on a global and regional scale. Here one important task is to understand and quantify the mechanisms that control moistening and dehydration of the upper troposphere / lower stratosphere from polar regions to the tropics. A key sub-task here is the investigation of the tropopause dynamics and the stratosphere-troposphere exchange processes. Further is necessary to improve our knowledge on the separation of water into gaseous and ice phases in cirrus clouds. On a more technical level it will be inevitable to provide a new, bias free reference for calibrating other remote sensing techniques, thereby unifying the global observational network for humidity in order to permit accurate regional trend analyses. All these tasks require globally available, essentially bias-free, vertically highly resolved and uncorrelated measurements of the water vapor profile. Current and possible near future space-borne passive observing systems fail to meet these requirements. The active differential absorption LIDAR (DIAL) method on the other hand has the potential to fulfill all these needs. A mission employing such an active system was proposed to ESAs Earth Explorer Program under the name WALES. As a contribution to this effort the German Aerospace Center (DLR) developed an airborne demonstrator which implements all essential features of a possible space-borne instrument, for example a multi-wavelength approach in the 935 nm absorption band of H2O and the usage of state-of-the art solid state laser technology. With this instrument a large data set has been gathered in various airborne campaigns devoted to different topics concerning the atmospheric part of the global water vapor cycle over the past years. We will present a selection of results from these campaigns and comparisons to other measurement techniques, both in-situ and remote which cover the whole troposphere up to the UTLS.