Towards gridded nighttime aerosol optical thickness retrievals using VIIRS day–night band observations over regions with artificial light sources

Using observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) day–night band (DNB), we examined the feasibility of developing a gridded nighttime aerosol optical thickness (AOT) data set based on the spatial derivative of measured top-of-atmosphere attenuated upwelling artificial lights at night (ALAN) over the US, Middle East, and Indian Subcontinent regions for 2017. We also studied the potential of using NASA's standard operational Black Marble nighttime lights product suite (VNP46) for estimating the spatial derivatives of surface artificial-light emissions, which is one of the key lower boundary conditions for the retrieval process. The sensitivity of nighttime aerosol retrievals to observing conditions and different methods of estimating the spatial derivative of surface artificial-light emissions were also explored. Root-mean-square errors (RMSEs) of ? 0.15 and ? 0.18 and correlations of ? 0.8 and ? 0.6 were found between VIIRS nighttime AOT and Aerosol Robotic Network (AERONET) nighttime and daytime data, respectively, suggesting that the proposed gridded nighttime AOT retrievals have reasonable skill levels for potential data assimilation, air quality, and climate studies of significant events. We also found that NASA Black Marble products can be used to estimate the spatial derivative of surface artificial-light emissions for nighttime AOT retrievals over regions that are not frequently contaminated by aerosol plumes, such as the USA. This study demonstrated the feasibility of constructing a gridded nighttime AOT data, using artificial lights, for monitoring of nighttime aerosol events over large spatial and temporal domains. Given the deployment of VIIRS instruments (currently in orbit and forthcoming) aboard the NOAA Joint Polar Satellite System (JPSS) series satellites, this study can be viewed as a precursor for gridded nighttime AOT retrievals at both regional and global scales in the future. We also show that the use of the NASA Black Marble products, which would greatly save the processing time of this method, is challenging over regions with frequent aerosol pollution, such as the Indian Subcontinent, and further exploration is required.