11:45 AM - 12:00 PM
[ACG36-10] Modulation of Night Sky Brightness by Aerosol around the Capital Area in Japan
Keywords:Light Pollution, Night sky, Radiance, Aerosol, Mapping
In recent years, light pollution, which interferes with natural starry sky visibility due to increased outdoor lighting and urbanization, has become a major serious problem. The studies of mapping the climatological distribution of the night sky brightness, for example Falchi et al. [2016], had a significant, social and scientific impacts. However, previous studies in global scale were computationally expensive and did not represent interannual, seasonal, and daily atmospheric variations. To address this issue, we have developed a new model in this study, incorporating data from satellite observations considering daily changes of aerosol obtained from reanalysis data.
Aerosols have a positive role in increasing the intensity of light scattered by the atmosphere and the brightness of the night sky when their amount is large, but they also have a negative role in making it harder for light to diffuse to distant locations. To quantify the impact of aerosols, we used the following computational approach. We used the data obtained by Suomi-NPP, MODIS and MERRA-2. This model considers multiple factors, including atmospheric reflectance by multiple scattering, reflections to and from the ground surface, and 3D light diffusion that is modeled by convolution using the point spread function (PSF) derived from a Monte Carlo photon transfer simulation. We compared our result of spatial distribution with the results of Falchi et al. [2016], which confirmed our model's capability to accurately reproduce the brightness distribution, especially in urban areas.
In the study, modulation in the brightness of the night sky were shown on different time scales. In the year-by-year scale, artificial light source radiance related to human activity was the primary modulator, showing a decrease in night sky brightness during COVID-19. In the seasonal cycle, the night sky has a tendency to become darker in winter and brighter in late spring and early summer in urban areas, on the other hand, the mountain area tends to become darker in autumn and brighter in winter. This difference could be due to the impact of albedo on the ground surface caused by snowfall. Also, the lunar radiance and aerosol impact daily variation, and analysis of different types of aerosols confirmed the variation in the brightness of the night sky by aerosol events. This showed that the brightness of the night sky is impacted not only by naturally occurring aerosols, which vary with the meteorological field, but also by anthropogenic aerosols related to human activities.
In this study, we evaluated the impact of aerosols on the brightness of the night sky at different time scales. This will not only help quantify light pollution caused by urbanization, but also show that the optical thickness of aerosols can potentially be calculated from ground-based light sources, which is expected to be useful for a new nighttime aerosol observation technique.
Aerosols have a positive role in increasing the intensity of light scattered by the atmosphere and the brightness of the night sky when their amount is large, but they also have a negative role in making it harder for light to diffuse to distant locations. To quantify the impact of aerosols, we used the following computational approach. We used the data obtained by Suomi-NPP, MODIS and MERRA-2. This model considers multiple factors, including atmospheric reflectance by multiple scattering, reflections to and from the ground surface, and 3D light diffusion that is modeled by convolution using the point spread function (PSF) derived from a Monte Carlo photon transfer simulation. We compared our result of spatial distribution with the results of Falchi et al. [2016], which confirmed our model's capability to accurately reproduce the brightness distribution, especially in urban areas.
In the study, modulation in the brightness of the night sky were shown on different time scales. In the year-by-year scale, artificial light source radiance related to human activity was the primary modulator, showing a decrease in night sky brightness during COVID-19. In the seasonal cycle, the night sky has a tendency to become darker in winter and brighter in late spring and early summer in urban areas, on the other hand, the mountain area tends to become darker in autumn and brighter in winter. This difference could be due to the impact of albedo on the ground surface caused by snowfall. Also, the lunar radiance and aerosol impact daily variation, and analysis of different types of aerosols confirmed the variation in the brightness of the night sky by aerosol events. This showed that the brightness of the night sky is impacted not only by naturally occurring aerosols, which vary with the meteorological field, but also by anthropogenic aerosols related to human activities.
In this study, we evaluated the impact of aerosols on the brightness of the night sky at different time scales. This will not only help quantify light pollution caused by urbanization, but also show that the optical thickness of aerosols can potentially be calculated from ground-based light sources, which is expected to be useful for a new nighttime aerosol observation technique.