Measuring Night‐Sky Brightness with a Wide‐Field CCD Camera

Under stable atmospheric conditions the brightness of the urban sky varies throughout the night following the time course of the anthropogenic emissions of light. Different types of artificial light sources (e.g. streetlights, residential, and vehicle lights) have specific time signatures, and this feature makes it possible to estimate the amount of brightness contributed by each of them. Our approach is based on transforming the time representation of the zenithal night sky brightness into a modal expansion in terms of the time signatures of the different sources of light. The modal coefficients, and hence the absolute and relative contributions of each type of source, can be estimated by means of a linear least squares fit. A practical method for determining the time signatures of different contributing sources is also described, based on wide-field time-lapse photometry of the urban nightscape. Our preliminary results suggest that, besides the dominant streetlight contribution, artificial light leaking out of the windows of residential buildings may account for a significant share of the time-varying part of the zenithal night sky brightness at the measurement locations, whilst the contribution of the vehicle lights seems to be significantly smaller.

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A survey of night sky brightness at College, Alaska

Transactions American Geophysical Union ◽

10.1029/tr031i004p00541 ◽

1950 ◽

Vol 31 (4) ◽

pp. 541 ◽

Cited By ~ 1

Author(s):

John B. Wilcox

Keyword(s):

Sky Brightness ◽

Night Sky ◽

Night Sky Brightness

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Remote Sensing of Aerosols at Night with the CoSQM Sky Brightness Data

10.20944/preprints202108.0181.v1 ◽

2021 ◽

Author(s):

Charles Marseille ◽

Martin Aubé ◽

Africa Barreto Velasco ◽

Alexandre Simoneau

Keyword(s):

Remote Sensing ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Low Cost ◽

Empirical Relationship ◽

Important Indicator ◽

Sky Brightness ◽

Night Sky ◽

Remote Sensing Techniques ◽

Night Sky Brightness

The aerosol optical depth is an important indicator of aerosol particle properties and associated radiative impacts. AOD determination is therefore very important to achieve relevant climate modeling. Most remote sensing techniques to retrieve aerosol optical depth are applicable to daytime given the high level of light available. The night represents half of the time but in such conditions only a few remote sensing techniques are available. Among these techniques, the most reliable are moon photometers and star photometers. In this paper, we attempt to fill gaps in the aerosol detection performed with the aforementioned techniques using night sky brightness measurements during moonless nights with the novel CoSQM: a portable, low cost and open-source multispectral photometer. In this paper, we present an innovative method for estimating the aerosol optical depth by using an empirical relationship between the zenith night sky brightness measured at night with the CoSQM and the aerosol optical depth retrieved at daytime from the AErosol Robotic NETwork. Such a method is especially suited to light-polluted regions with light pollution sources located within a few kilometers of the observation site. A coherent day-to-night aerosol optical depth and Ångström Exponent evolution in a set of 354 days and nights from August 2019 to February 2021 was verified at the location of Santa Cruz de Tenerife on the island of Tenerife, Spain. The preliminary uncertainty of this technique was evaluated using the variance under stable day-to-night conditions, set at 0.02 for aerosol optical depth and 0.75 for Ångström Exponent. These results indicate the set of CoSQM and the proposed methodology appear to be a promising tool to add new information on the aerosol optical properties at night, which could be of key importance to improve climate predictions.

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