International Research Fellowship Program: Development of a Metropolis-Hastings Algorithm for Retrieving Aerosol Properties and Their Uncertainties from High Spectral Resolution

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0856648HermanThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four month research fellowship by Dr. Benjamin Herman to work with Drs. Johanna Tamminen and Gerrit de Leeuw at the Finnish Meteorological Institute in Finland.Atmospheric aerosols have an important impact on our environment due to processes that result from their interaction with cloud formation and how they reflect and absorb solar and thermal radiances. They affect climate change through their affects in the radiation budget both directly from their own influence and indirectly from their effects in cloud dynamics. The role of aerosols in cloud dynamics also has an influence on precipitation and thus also the water cycle, which has its own effect on climate in addition to its importance in water resources. A high spectral resolution lidar (HSRL) instrument has already been developed at NASA-Langley that can measure range-resolved aerosol optical properties, specifically back-scattering and depolarization coefficients at infrared (1064nm) and visible (532nm) wavelengths, and extinction coefficient (the degree to which light is attenuated) at 532nm. This project addresses the problem of how to determine other aerosol properties, specifically volume and surface area concentrations, optical absorption, and total scattering from these measurements. The complexity of aerosols means that the five optical properties measured by this lidar instrument cannot give a single definitive description of an aerosol. Instead what is available is a probability distribution that represents uncertainty and is based on measurement errors and knowledge of probable aerosol states in the absence of measurements. The goal of this project is to develop Markov chain Monte Carlo algorithms and aerosol models for processing data from the HSRL instrument to estimate aerosol properties and assess their uncertainties. The project is in collaboration with Dr. Johanna Tamminen and Dr. Gerrit de Leeuw at the Finnish Meteorological Institute and the University of Helsinki. Their combined expertise is an excellent contribution to the development of these data processing algorithms. Dr. Tamminen is experienced in Markov chain Monte Carlo methods while Dr. de Leeuw?s experience is in optical sensing of aerosols. This project is also parallel with the research interests of the Finnish Meteorological Institute, which has a Raman lidar instrument that takes measurements similar to the HSRL.Ultimately, these algorithms may provide the foundation for constructing additional algorithms that analyze data from multiple instruments in the worldwide earth observing system, enabling a better understanding of environmental processes.