  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.
