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[ACG37-P22] Quantitative Evaluation of Night Sky Brightness in Japan Considering Atmospheric Environment
Keywords:Light Pollution, Night sky, Radiance, Aerosol
1. Introduction
In recent years, Japan has been facing the problem of urbanization, where the population is concentrated in cities and various problems occur. One such problem is "light pollution." About 70% of the Japanese population lives in areas where the Milky Way is not visible, and globally, the area of the earth's surface illuminated by artificial light is expanding by about 2% every year.
It is now obvious that unnecessary lighting at night is seriously disrupting the ecosystems that connect animals, plants, and the world, and that these effects extend far beyond the city. In ecosystems, past studies have provided ample evidence that artificial light sends a variety of off-timing signals to at least 160 species in nature.
In this context, there have not been many studies on light pollution in Japan. In this study, to quantitatively evaluate light pollution and clarified the relationship between atmospheric conditions and night sky brightness, a mathematical model was developed.
2. Satellite data
Period: 2021/01/01-2021/12/31
Area: Including Sendai City, 140-142°E, 37-39°N
Satellite data used for calculations:
VIIRS/ VNP46A2; Radiance
MODIS/MOD09CMG; Surface reflectance
MERRA2_tavg1_2d_aer_Nx; Scattering AOT, Extinction AOT
3. Method
The atmosphere is considered as a parallel plane, and upward and downward radiation are assumed to be isotropic, respectively. Using as input data the values of urban radiance, emitted from the ground to the atmosphere, surface reflectance, and atmospheric aerosols, the brightness of the night sky is simulated by calculating the downward radiance using the "two-stream approximation" method of radiative transfer.
4. Results
Simulations of changes in night sky brightness around the city of Sendai as a function of aerosol optical depth (AOD) were performed to clarify the relationship between AOD and night sky brightness using average annual urban radiance and aerosol coefficients (including terrestrial and oceanic particles) in 2021.
Analysis of the distribution of night sky brightness on the dates when the maximum and minimum daily average daily AODs were observed for the year 2021 in the analyzed area showed that the brightness of the night sky on the dates when the maximum values were observed was about 10 times greater than that on the dates when the minimum values were observed.
By calculating the relationship of night sky brightness against AOD, the brightness of the night sky could be quantitatively evaluated.
In recent years, Japan has been facing the problem of urbanization, where the population is concentrated in cities and various problems occur. One such problem is "light pollution." About 70% of the Japanese population lives in areas where the Milky Way is not visible, and globally, the area of the earth's surface illuminated by artificial light is expanding by about 2% every year.
It is now obvious that unnecessary lighting at night is seriously disrupting the ecosystems that connect animals, plants, and the world, and that these effects extend far beyond the city. In ecosystems, past studies have provided ample evidence that artificial light sends a variety of off-timing signals to at least 160 species in nature.
In this context, there have not been many studies on light pollution in Japan. In this study, to quantitatively evaluate light pollution and clarified the relationship between atmospheric conditions and night sky brightness, a mathematical model was developed.
2. Satellite data
Period: 2021/01/01-2021/12/31
Area: Including Sendai City, 140-142°E, 37-39°N
Satellite data used for calculations:
VIIRS/ VNP46A2; Radiance
MODIS/MOD09CMG; Surface reflectance
MERRA2_tavg1_2d_aer_Nx; Scattering AOT, Extinction AOT
3. Method
The atmosphere is considered as a parallel plane, and upward and downward radiation are assumed to be isotropic, respectively. Using as input data the values of urban radiance, emitted from the ground to the atmosphere, surface reflectance, and atmospheric aerosols, the brightness of the night sky is simulated by calculating the downward radiance using the "two-stream approximation" method of radiative transfer.
4. Results
Simulations of changes in night sky brightness around the city of Sendai as a function of aerosol optical depth (AOD) were performed to clarify the relationship between AOD and night sky brightness using average annual urban radiance and aerosol coefficients (including terrestrial and oceanic particles) in 2021.
Analysis of the distribution of night sky brightness on the dates when the maximum and minimum daily average daily AODs were observed for the year 2021 in the analyzed area showed that the brightness of the night sky on the dates when the maximum values were observed was about 10 times greater than that on the dates when the minimum values were observed.
By calculating the relationship of night sky brightness against AOD, the brightness of the night sky could be quantitatively evaluated.