Multiple Angle Observations Would Benefit Visible Band Remote Sensing Using Night Lights

The spatial and angular emission patterns of artificial and natural light emitted, scattered, and reflected from the Earth at night are far more complex than those for scattered and reflected solar radiation during daytime. In this commentary, we use examples to show that there is additional information contained in the angular distribution of emitted light. We argue that this information could be used to improve existing remote sensing retrievals based on night lights, and in some cases could make entirely new remote sensing analyses possible. This work will be challenging, so we hope this article will encourage researchers and funding agencies to pursue further study of how multi‐angle views can be analyzed or acquired.
Plain Language Summary: When satellites take images of Earth, they usually do so from directly above (or as close to it as is reasonably possible). In this comment, we show that for studies that use imagery of Earth at night, it may be beneficial to take several images of the same area at different angles within a short period of time. For example, different types of lights shine in different directions (street lights usually shine down, while video advertisements shine sideways), and tall buildings can block the view of a street from some viewing angles. Additionally, since views from different directions pass through different amounts of air, imagery at multiple angles could be used to obtain information about Earth's atmosphere, and measure artificial and natural night sky brightness. The main point of the paper is to encourage researchers, funding agencies, and space agencies to think about what new possibilities could be achieved in the future with views of night lights at different angles.
Key Points: Remote sensing using the visible band at night is more complex than during the daytime, especially due to the variety of artificial lights. Views of night lights intentionally taken from multiple angles provide several advantages over near‐nadir or circumstantial view geometries. Night lights remote sensing would benefit from greater consideration of the role viewing geometry plays in the observed radiance.
EC H2020 H2020 Societal Challenges http://dx.doi.org/10.13039/100010676
Helmholtz Association http://dx.doi.org/10.13039/501100009318
Slovak Research and Development Agency
Xunta de Galicia (Regional Government of Galicia) http://dx.doi.org/10.13039/501100010801
National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
University of Hong Kong http://dx.doi.org/10.13039/501100003803
Fonds de recherche du Québec
EC Emprego, Assuntos Sociais e Inclusão European Social Fund http://dx.doi.org/10.13039/501100004895
Natural Environment Research Council http://dx.doi.org/10.13039/501100000270
City of Cologne, Germany