Satellite-based remote sensing of the urban atmosphere: examples from German cities

The major goal of the German research project Urban Climate Under Change [UC]² is the development and evaluation of an innovative urban climate model that should be able to simulate atmospheric processes on spatial scales of 10 m or finer for entire cities like Berlin and Stuttgart. This will enable interdisciplinary analyzes for the planning of measures to improve the urban climate and air quality. For the evaluation of urban climate models and mesoscale chemical-transport models and the three-dimensional processes represented therein, reference measurements are usually only available in the lowest meters of the boundary layer. In addition, an evaluation of city-wide mass balances (e.g. of air pollutants) with point measurements at the surface is only possible under many assumptions, the uncertainties remain high. Satellite and aircraft-based observations are therefore an inevitable addition to the analysis of the urban climate and the evaluation of three-dimensional urban climate models and chemical-transport models, especially if they cover entire cities or agglomerations. The objective of the work presented here is the analysis of atmospheric and chemical parameters by satellite and airborne measurements in order to examine the variability of the urban atmosphere and thereby contribute to the evaluation of the urban climate model PALM-4U and the mesoscale chemical-transport model POLYPHEMUS/DLR. In addition of long-term observations, results from the new instrument Sentinel-5P/TROPOMI will be shown. The capability of the instrument to monitor urban pollution plumes and urban pollution islands is examined. Airborne in-situ measurements were carried out with the DLR Cessna during two intensive measurement campaigns (IOP) in Berlin and Stuttgart