Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> By accounting for surface-based light source emissions and Top-of-Atmosphere (TOA) downward lunar fluxes, we adapted the Spherical Harmonic Discrete Ordinate Method (SHDOM) 3-dimentional (RTM) radiative transfer model (RTM) to simulate nighttime 3-D TOA radiances as observed from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night-Band (DNB) onboard the Suomi-NPP satellite platform. Used previously for daytime 3D applications, new SHDOM enhancements allow for the study of the impacts of various observing conditions and aerosol properties on simulated VIIRS-DNB TOA radiances. Observations over Dakar, Senegal, were investigated for potential applications and opportunities for using observed radiances containing VIIRS-DNB ‘bright pixels’ from artificial light sources to conduct aerosol retrievals. We found that using the standard deviation (STD) of such bright-pixels provided a more stable quantity for nighttime aerosol optical depth (AOD) retrievals than direct retrievals from TOA radiances. Further, both the mean TOA radiance and STD of TOA radiances over artificial sources are significantly impacted by satellite viewing angles. Light domes, the enhanced radiances adjacent to artificial light sources, are strong functions of aerosol properties and especially aerosol vertical distribution, which may be further utilized for retrieving aerosol layer height in future studies. Through inter-comparison with both day- and night-time Aerosol Robotic Network (AERONET) data, the feasibility of retrieving nighttime AODs using 3-D RTM SHDOM over artificial light sources was demonstrated. Our study shows strong potential for using artificial light sources for nighttime AOD retrievals, while also highlighting larger uncertainties in quantifying surface light source emissions. This study underscores the need for surface light emission source characterizations as a key boundary condition, which is a complex task that requires enhanced input data and further research. We demonstrate how quality-controlled nighttime light data from the NASA’s Black Marble product suite could serve as a primary input into estimations of surface light source emissions for nighttime aerosol retrievals.
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