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Min, M.; Zheng, J.; Zhang, P.; Hu, X.; Chen, L.; Li, X.; Huang, Y.; Zhu, L. |
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A low-light radiative transfer model for satellite observations of moonlight and earth surface light at night |
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Journal Article |
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2020 |
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Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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in press |
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106954 |
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Remote Sensing; Instrumentation |
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Abstract |
Lunar sun-reflected light can be effectively measured through a low-light band or a day/night band (DNB) implemented on space-based optical sensors. Based on moonlight, nocturnal observations for artificial light sources at night can be achieved. However, to date, an open-sourced and mature Low-Light Radiative Transfer Model (LLRTM) for the further understanding of the radiative transfer problem at night is still unavailable. Therefore, this study develops a new LLRTM at night with the correction of the lunar and active surface light sources. First, the radiative transfer equations with an active surface light source are derived for the calculation based on the lunar spectral irradiance (LSI) model. The simulation from this new LLRTM shows a minimal bias when compared with the discrete ordinates radiative transfer (DISORT) model. The simulated results of radiance and reflectance at the top of the atmosphere (TOA) also show that the surface light source has a remarkable impact on the radiative transfer process. In contrast, the change in the lunar phase angle has minimal influence. Also, comparing with space-based DNB radiance observations, LLRTM shows the potential to simulate space-based low-light imager observations under an effective surface light source condition during the night. |
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0022-4073 |
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GFZ @ kyba @ |
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2850 |
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Ściężor, T. |
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The impact of clouds on the brightness of the night sky |
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Journal Article |
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2020 |
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Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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in press |
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106962 |
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Skyglow |
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Clouds are a kind of atmospheric factor that most effectively scatters the artificial light coming from the ground. Therefore, they have the most significant impact on the brightness of the night sky. The paper analyses the influence of both the level of cloudiness, as well as the genera of clouds and altitude of its base, on amplifying of the light pollution. The impact of cloudiness on the brightness of the night sky in places with different levels of light pollution was researched. Measurements of meteorological elements were used together with clouds genera assessments. The introduction of an innovative method of identifying some genera of clouds on the base of the all-night continuous measurements of the sky's brightness allowed for a similar analysis in the absence of observational data specifying the genera of clouds.
A linear correlation between the cloudiness and the brightness of the night sky was found. The determined linear correlation parameters allow for specifying the three types of light-polluted areas, possibly related to the density of population. It was found that among the nine genera of the identified night clouds, the Altocumulus, Cirrocumulus, and Cumulonimbus ones are responsible for this correlation. No dependence of the brightness of the night sky on the clouds’ albedo was found. In case of overcast sky, there was a clear relationship between the average altitude of the individual genus of clouds and the brightness of the night sky. Most of the night sky brightness comes from the light scattered on the lowest altitude clouds genera, while the least contribution comes from the light scattered on the high-level clouds. It was also found that at the freezing temperatures, the layer of aerosols forms below the level of the genera Nimbostratus or Stratus. This layer, thickening with the decreasing temperature, additionally scatters the artificial light. |
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2859 |
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Tong, K.P.; Kyba, C.C.M.; Heygster, G.; Kuechly, H.U.; Notholt, J.; Kolláth, Z. |
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Angular distribution of upwelling artificial light in Europe as observed by Suomi–NPP satellite |
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Journal Article |
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2020 |
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Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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in press |
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in press |
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Remote Sensing; Skyglow |
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Measuring the angular distribution of upwelling artificial light is important for modeling light pollution, because the direction of emission affects how light propagates in the atmosphere. We characterize the angular distributions of upwelling artificial light for Europe and northern Africa in 2018, based on night time radiance data for clear nights without twilight and moonlight from the VIIRS–DNB sensor on board the Suomi NPP satellite. We find that in general, suburban areas of major cities emit more light at larger zenith angles, whereas the opposite can be seen at the city centers, where the highest radiance is directed upward. The mean numbers of overflights for the year is 83, meaning that there are on average approximately seven suitable overflights per month. Future analysis may consider using moonlight models to compensate for the retrieval of moonlit scenes and analyzing data from different years in order to expand the amount of available data. As the VIIRS–DNB sensor on board the NOAA–20 satellite (launched 2017) has almost the same design, this method can also be extended to the data taken by NOAA–20. |
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0022-4073 |
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GFZ @ kyba @ |
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2880 |
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Jechow, A.; Kyba, C.C.M.; Hölker, F. |
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Title |
Mapping the brightness and color of urban to rural skyglow with all-sky photometry |
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Journal Article |
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2020 |
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Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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in press |
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in press |
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Skyglow |
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Artificial skyglow is a form of light pollution with wide ranging implications on the environment. The extent, intensity and color of skyglow depends on the artificial light sources and weather conditions. Skyglow can be best determined with ground based instruments. We mapped the skyglow of Berlin, Germany, for clear sky and overcast sky conditions inside and outside of the city limits. We conducted observations using a transect from the city center of Berlin towards a rural place more than 58 km south of Berlin using all-sky photometry with a calibrated commercial digital camera and a fisheye lens. From the multispectral imaging data, we processed luminance and correlated color temperature maps. We extracted the night sky brightness and correlated color temperature at zenith, as well as horizontal and scalar illuminance simultaneously. We calculated cloud amplification factors at each site and investigated the changes of brightness and color with distance, particularly showing differences inside and outside of the city limits. We found high values for illuminance above full moon light levels and amplification factors as high as 25 in the city center and a gradient towards the city limit and outside of the city limit. We further observed that clouds decrease the correlated color temperature in almost all cases. We discuss advantages and weaknesses of our method, compare the results with modeled night sky brightness data and provide recommendations for future work. |
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0022-4073 |
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GFZ @ kyba @ |
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2895 |
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Author |
Kocifaj, M.; Kundracik, F. |
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Multi-wavelength radiometry of aerosols designed for more accurate night sky brightness predictions |
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Journal Article |
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Year |
2020 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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250 |
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106998 |
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Keywords |
Skyglow; Remote Sensing |
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Scattering by aerosols and gases cause a certain fraction of artificial light emitted upwards is redirected to the ground. Of all atmospheric constituents just the aerosols are most important modulators of night-sky brightness under cloudless conditions. Unlike most of the previous we highlight a crucial role of solar radiometry for determining the atmospheric optical depth before night-time observation is to be made. Aerosol optical depth at visible wavelengths extracted from the data measured provides then the information on size distribution or mean refractive index of aerosol particles that in turn are both necessary to make night sky brightness prediction more accurate. Therefore, combining daytime and night-time radiometry we can achieve accuracy much higher than ever before. This is due to significantly reduced uncertainty in aerosol properties.
The aerosol data are retrieved from a new portable multi-wavelength optical analyzer that operates Ocean Optics spectrometer. The equipment provides the radiance data from 350 nm to 1000 nm with spectral resolution of 1 nm. Due to high sun radiance levels we use a system of mirrors each reducing the signal to about 4%, while keeping the integration time short. The minimum integration time of 3 ms allows for detection of direct sunlight. The system developed is sensitive to small changes in the aerosol system, while showing a good detection limit even under low turbidity conditions. The system performance is demonstrated in field experiment conducted shortly after front passage when most of aerosol particles is effectively removed by rain. |
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0022-4073 |
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GFZ @ kyba @ |
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2906 |
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