My main research interest is the role of aerosol and clouds in the climate system, which I try to better understand using remote-sensing approaches. During my PhD research (U Marburg, Germany) I developed an operational technique to retrieve fog properties and patterns from passive-sensor satellite data. Later, I complemented this by ground-based observations (ceilometer, FMCW radar) in the context of various EU COST actions. As a PostDoc, I became interested in the role of aerosols around clouds (stay at U Washington, Seattle, WA, USA), which, at ETH Zurich (Switzerland), I put into the context of the global climate system and the evaluation of global climate model output. As a professor of climatology (U Bochum, Germany) I began combining my low cloud property retrievals with aerosol-cloud-interactions research by focusing on boundary-layer clouds using a range of passive and active sensor remote sensing observations. Statistical methods (stay at NOAA, Boulder, CO, USA) play an important role in my approaches to system understanding. At Karlsruhe Institute of Technology (KIT, Karlsruhe, Germany) I contribute to the work of the Institute of Photogrammetry and Remote Sensing and the Institute of Meteorology and Climate Research.