Colour remote sensing of the impact of artificial light at night (II): Calibration of DSLR-based images from the International Space Station.

Nighttime images taken with DSLR cameras from the International Space Station (ISS) can provide valuable information on the spatial and temporal variation of artificial nighttime lighting on Earth. In particular, this is the only source of historical and current visible multispectral data across the world (DMSP/OLS and SNPP/VIIRS-DNB data are panchromatic and multispectral in the infrared but not at visible wavelengths). The ISS images require substantial processing and proper calibration to exploit intensities and ratios from the RGB channels. Here we describe the different calibration steps, addressing in turn Decodification, Linearity correction (ISO dependent), Flat field/Vignetting, Spectral characterization of the channels, Astrometric calibration/georeferencing, Photometric calibration (stars)/Radiometric correction (settings correction - by exposure time, ISO, lens transmittance, etc) and Transmittance correction (window transmittance, atmospheric correction). We provide an example of the application of this processing method to an image of Spain. • DLSR cameras can provide accurate radiometric measurements. • ISS nighttime images using DSLR cameras can provide colour data. • Spatial resolution increased by 150–1000 times compared to popular platforms. • This opens up new possibilities for environmental studies. [ABSTRACT FROM AUTHOR]