Characterisation of night-time outdoor lighting in urban centres using cluster analysis of remotely sensed light emissions

Evidence of the negative impact of light pollution on ecosystems is increasing every year. Its monitoring and study requires the identification, characterisation and control of the emitting sources. This is the case of urban centres with outdoor lighting that spills light outside the place it is intended to illuminate. The quantity and nature of the pollutant (artificial light at night) depends on the lamps used and how they are positioned, which is important because a greater proportion of blue light means a greater scattering effect. In this study, we analysed the emissions of 100 urban centres in the north of Granada province (Spain), using images from International Space Station (ISS) in 2012 and 2021, and compared the results with public lighting inventories and with data from the VIIRS instrument. Using inference and cluster analysis techniques, we confirmed an overall increase in emissions and a shift in their colour towards blue, consistent with the results of the lighting inventory analysis. However, there is a discrepancy with the results obtained from VIIRS images, which is explained by the lack of sensitivity of this instrument to blue light. We concluded that the analysis of ISS images is a powerful tool for the study and characterisation of street lighting and its evolution, especially when the changes occur in the blue band.