Can we observe the atmosphere by street lamps? Examining the potential for use of anthropogenic light emissions in atmospheric retrievals

Nighttime detection and characterization of atmospheric aerosol is made difficult by a lack of observable visible radiation and limited thermal contrast between the surface and low-altitude aerosol plumes. The Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB), which is sensitive to very low levels of visible light (as low as 10-9 Wxcm-2sr-1), has proven useful for cloud characterization at night and is being studied for use in quantitative aerosol optical depth retrievals. However, since moonlight is not available on all nights, our retrievals are left in the dark on roughly half of all nights. In this study we assess the potential for surface-based anthropogenic light emission sources to be exploited in the context of aerosol retrievals—using their attenuation and light-diffusion properties as a proxy for characterizing the intervening aerosol layer. In order to be useful for in this capacity, a given light source must be well characterized. Namely, its intensity must be stable and predictable as a function of viewing geometry. To assess the predictability of anthropogenic lighting, we have enlisted a full year of cloud masked VIIRS DNB data to develop a radiance database, remapped to a standard grid, and considered several types of anthropogenic light sources. The variable stability of these light sources is assessed and used to determine which light sources may be most viable for aerosol optical depth retrievals.