Testing Sky Brightness Models Against Radial Dependency: A Dense Two Dimensional Survey Around The City Of Madrid, Spain: Sqm Data

We present a study of the night sky brightness around the extended<br> metropolitan area of Madrid using Sky Quality Meter (SQM) photometers. The map is the first to cover the spatial distribution of the sky brightness in the<br> center of the Iberian peninsula. These surveys are neccessary to test the light<br> pollution models that predict night sky brightness as a function of the<br> location and brightness of the sources of light pollution and the scattering of<br> light in the atmosphere. We describe the data-retrieval methodology, which<br> includes an automated procedure to measure from a moving vehicle in order to<br> speed up the data collection, providing a denser and wider survey than previous<br> works with similar time frames. We compare the night sky brightness map to the<br> nocturnal radiance measured from space by the DMSP satellite. We find that i) a<br> single source model is not enough to explain the radial evolution of the night<br> sky brightness, despite the predominance of Madrid in size and population, and<br> ii) that the orography of the region should be taken into account when deriving<br> geo-specific models from general first-principles models. We show the tight<br> relationship between these two luminance measures. This finding sets up an<br> alternative roadmap to extended studies over the globe that will not require<br> the local deployment of photometers or trained personnel.