The contribution of scattered radiation to the upward radiance of a city

Abstract

Remote sensing of nighttime urban light emissions becomes a common part of light pollution modeling. Radiance data gathered by various satellites scanning the Earth surface serve as important inputs for estimating the upward luminous flux of a city, which then allows to evaluate the level of light pollution in its surroundings. The easiest way is to assume the measured radiance of a city pixel as belonging to its direct radiation. However, this radiance is ”contaminated” by scattered radiation coming from the light emitting surroundings of the pixel. In principle, this diffuse light contribution can influence the estimate of the emitted flux. In this paper, we developed a model to assess how important such a contribution can be for cities of different shapes and sizes. The numerical simulations for real city patterns obtained from the VIIRS-DNB database reveal, that scattered radiation could make up on average about 10%–20% of the total upward radiance of a pixel under quite obvious aerosol conditions. We have also derived two simplified models for idealized city patterns which enable relatively simple estimation of the diffuse radiation contribution without the need of complex simulations for realistic cities.