High-resolution image of Berlin at night facilitates light pollution research

Researchers from Berlin have published an 878 megapixel aerial mosaic image of Berlin at night. With one pixel per square meter, the resulting map is the highest resolution image ever published of a city at night. The ecologists from the Leibniz Institute of Freshwater Ecology and Inland Fisheries and physicists from Freie Universität Berlin used the image to measure how much light comes from different types of land use areas, such as streets or parks. Their findings were recently published in the journal Remote Sensing of Environment.

The scientists are studying light pollution, the modification of natural light levels in the nocturnal environment due to artificial light from cities.. Their goals are to understand both what the sources of upwards directed light are, and to identify patterns in the distribution of the lights. To do this, they stitched together a total of 2647 aerial photographs taken from the research aircraft of Freie Universität Berlin's Institute for Space Sciences. The photos were taken in a series of 14 tracks at 3 km above the city in September of 2010.

A total of 42 percent of Berlin's area, including all of the city's central neighborhoods, was analyzed by comparing the light emitted from each point to land use information about the city. The scientists found that more than one third of the upward directed light came from streets, which are lit by streetlights, auto headlights, and advertisements. The city's sources of light were found to be unevenly distributed, with half of the total light coming from only one quarter of its area. Part of the reason for this is that Berlin still contains large unlit areas such as the Havel River, Grunewald, and Tempelhofer Park. The researchers noted that these areas are important dark resources for nocturnal animals. In total, the researchers found that such natural areas accounted for almost one third of the study area, but emitted only 6 percent of the total light.

The research was funded by two interdisciplinary projects, MILIEU (Freie Universität Berlin) and "Verlust der Nacht," a joint project of Leibniz Institute of Freshwater Ecology and Inland Fisheries and Freie Universität Berlin. "Verlust der Nacht" is funded by the German Ministry of Education and Research (BMBF) and the Senate Department for Economics, Technology, and Research.