Remote Sensing of deep convective clouds - A new satellite view
Final Report Abstract
The cloud scanner sensor is a central part of the three-dimensional cloud and aerosol interaction mission (CLAIM-3D) - a satellite remote sensing concept recently proposed by Dr. Martins and colleagues at NASA Goddard Space Flight Center in the US. CLAIM-3D combines measurements of aerosol characteristics in the vicinity of clouds and of profiles of cloud microphysical characteristics. Such a set of collocated measurements will allow new insights in the complex field of cloud-aerosol interactions affecting directly the development of clouds and precipitation, especially in convection. The cloud scanner measures radiance reflected or emitted by cloud sides at several wavelengths to derive a profile of cloud particle size and thermodynamic phase. For the retrieval of effective size a new statistical retrieval was proposed by Dr. Marshak and colleagues at NASA accounting for the complex three-dimensional (3D) nature of cloud geometry and radiative transfer, since a spatial high resolution (~ 100 m) is prerequisite to measure profiles of microphysics for clouds of a few kilometres vertical extent. Up to now, existing passive remote sensing techniques, based on simplified ID radiative transfer, are not able to provide useful information neither on such a resolution nor on this kind of optically thick clouds. In this project the potential of the new approach was tested in realistic cloud observing situations in a fully simulated environment: (1) Cloud resolving modelling provided complex 3D structures of ice, water and mixed phase clouds, from the early stage of convective development to mature deep convection; (2) 3D radiative transfer modelling was used to realistically simulate the aspired observations. A large number of cloud data sets and related simulated observations were conducted to obtain the database for an experimental statistical (Bayesian) retrieval. It could be shown that regardless of the high spatial complexity of realistic cloud structures and 3D radiative transfer, the signatures of cloud particle effective radius and cloud phase were clearly detectable in a statistical sense (for a feasibility study for a ground based sensor please see poster at http://stm.arm.gov/posters/07awards.stm). This fact is used to employ the simulation database as starting point of a prototype Bayesian retrieval of effective radius accounting for realistic cloud structure and 3D radiative transfer. In contrast to fast ID radiative transfer simulations used for standard cloud property retrievals, the computational effort for 3D radiative transfer simulations necessary for the development of a 3D retrieval was only feasible after the introduction of new variance reduction techniques into the employed state-of-the-art Monte Carlo model. A proof-of-concept was provided for the possibility to measure accurate cloud property profiles on a high spatial resolution based on the proposed cloud side remote sensing approach (see also NASA Climate and Radiation Branch "Image of the Week" at http://climate.gsfc.nasa.gov/imageArchive.php for December 2007). In the near future the retrieval database will be extended in the hosting group of this project at NASA Goddard to include more solar illumination geometries and become applicable to cloud side measurements collected at NASA and hopefully soon at the current working group of Dr. Zinner at Deutsches Zentrum für Luft- und Raumfahrt (DLR). Measurements collected will be jointly analysed at both groups and new insights into convective cloud physics and its interaction with aerosol will be gained.
Publications
- "Derivation of Realistic High-resolution Cloud Structure", November 2006
T. Zinner and A. Marshak
- A-Train symposium, Lille, France, October 2007: "Statistical Retrieval for Passive Remote Sensing of Deep Convection"
T. Zinner, A. Marshak, J.V. Martins, and S. Lang
- ARM Science Team Meeting, Monterey, CA, USA, March 2007: "Remote Sensing of Cloud Sides of Deep Convective Clouds"
T. Zinner, A. Marshak, J.V. Martins, X. Li, S. Lang, and W.-K. Tao
- Gordon Research Conference on Radiation and Climate, New London, NH, USA, August 2007: "Remote Sensing of Cloud Sides of Deep Convective Clouds"
T. Zinner, A. Marshak, J.V. Martins, X. Li, S. Lang, and W.-K. Tao
- IUGG General Assembly, Perugia, Italy, July 2007, Session 3D Radiative Transfer in Complex Geophysical Media: "Cloud Microphysics Retrieval in a Highly Three-dimensional Situation"
T. Zinner, A. Marshak, J.V. Martins, and S. Lang
- IUGG General Assembly, Perugia, Italy, July 2007, Session Aerosols, Radiation and Clouds: "Remote sensing of cloud sides of deep convective clouds"
T. Zinner, A. Marshak, J.V. Martins, and S. Lang
