Impact of atmospheric effect and observation geometry on the directional distribution of blooming effect in VIIRS night-time light images

Blooming effect, a phenomenon that actual lit areas appear enlarged in nighttime light images acquired by satellites, has been widely studied in remote sensing community. However, the physical mechanisms behind its formation have not been quantitatively explored. In this study, we first reported a new and interesting phenomenon that the blooming effect exhibits an east-west elliptical shape at point light sources in VIIRS nighttime light images. Based on this observation we hypothesize that the blooming shape is influenced by the observation geometry (i.e., viewing zenith angle (VZA)) and atmospheric scattering. To test this hypothesis, the physical mechanism behind the formation of the blooming shape through numerical simulations using the Method of Successive Orders of Scattering (MSOS) model was revealed. More than 1000 numerical simulations were conducted using MSOS model under various aerosol conditions, observation geometries, and wavelengths, revealing a positive correlation between the eccentricity of the blooming shape and VZA, with R² values exceeding 0.9. To validate these findings with satellite observations, we analyzed VNP46A1 data of Black Marble product from 10 gas flaring regions worldwide. The results reconfirmed the positive correlation between the eccentricity of the blooming shape and VZA across all the selected regions, with R² values exceeding 0.5. Both numerical simulations and satellite observations supported the hypothesis. This study revealed the physical mechanism behind the blooming effect, suggesting that physical models are important to understand and advance nighttime light remote sensing.