Model for Artificial Night-Sky Illumination

Abstract

A model has been constructed to allow calculation of the night-sky brightness caused by a city at its center and outside the city, and at arbitrary zenith distances. A circular city of uniform brightness is assumed, with the total brightness proportional to the population. Molecular scattering and aerosol scattering are included, with the amount of aerosols being an adjustable parameter, and different scale heights being adopted for molecules and aerosols. The reflectivity of the ground and the fraction of light radiated above the horizontal are taken as parameters. Applications are given to several cities, to the general population-distance relations, to brightness-distance relations, and to the city center brightness-population relations.

The artificial night sky brightness mapped from DMSP satellite Operational Linescan System measurements

“…Therefore in the computation of the total light flux S that molecules and aerosols in the infinitesimal volume scatter toward the observer we take into account light already scattered once. We assumed, as Garstang (1984Garstang ( , 1986, that the light coming to the considered infinitesimal volume along the line of sight after a scatter has approximately a direction near that of the direct light, so that the scattering angle ω in first approximation is always the same. In this case the total illuminance S can be written:…”

The Artificial Sky Brightness in Europe Derived from DMSP Satellite Data

“…We obtained the propagation function f ((x, y), (x', y')) for each pair of points (x, y) and (x', y') using detailed models for the light propagation in the atmosphere based on the modelling technique introduced and developed by Garstang (1986Garstang ( , 1987Garstang ( , 1988Garstang ( , 1989aGarstang ( , 1989bGarstang ( , 1991aGarstang ( , 1991bGarstang ( , 1991cGarstang ( , 2000 and also applied by Cinzano (2000a,b,c). The models assume Rayleigh scattering by molecules and Mie scattering by aerosols and take into account extinction along the light path and Earth curvature.…”

“…We neglected the presence of sporadic denser aerosol layers at various heights or at ground level, the effects of the Ozone layer and the presence of volcanic dust. We take into account changes in aerosol content following Garstang (1986), introducing a parameter K which measures the relative importance of aerosol and molecules for scattering light. The adopted modelling technique allows an assessment of the atmospheric conditions for which a map is computed, giving observable quantities like the vertical extinction at sea level in magnitudes.…”

“…We choose to assume this function and check its consistency with satellite measurements, rather than directly determine it from satellite measurements because at very low elevation angles the spread is much too large to constrain adequately the function shape. We adopted for the average normalized emission function the normalized city emission function from Garstang (1986).…”

Light Pollution and Energy Loss from Cairo

“…Many investigators have studied light pollution (see e.g. Walker 1970Walker , 1973Walker , 1977Walker , 1988Treanor 1973;Berry 1976;Garstang 1984Garstang , 1986Garstang , 1988Garstang , 1991. However, only a limited number of investigators have studied the other face of light pollution, which is the electric energy loss.…”