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

TL;DR

This paper details a comprehensive calibration method for DSLR images taken from the ISS to accurately analyze artificial light at night, enabling valuable spatial and temporal light data across the globe.

Contribution

It introduces a detailed calibration pipeline for DSLR nighttime images from the ISS, enhancing their usability for studying artificial light at night.

Findings

Calibration steps improve image accuracy for light analysis

Processed images enable reliable spatial and temporal light variation studies

Method applied successfully to an example image of Spain

Abstract

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.