Abstract
Light pollution modelling and monitoring has traditionally used zenith
sky brightness as its main indicator. Several other indicators (e.g.
average sky radiance, horizontal irradiance, average sky radiance at
given interval of zenith distances) may be more useful, both for general
and for specific purposes of ecology studies, night sky and
environmental monitoring. These indicators can be calculated after the
whole sky radiance is known with sufficient angular detail. This means,
for each site, to integrate the contribution in each direction of the
sky of each light source in the radius of hundreds of km. This approach
is extremely high time consuming if the mapping is desired for a large
territory. Here we present a way to obtain maps of large territories for
a large subset of useful indicators, bypassing the need to calculate
first the radiance map of the whole sky in each site to obtain from it
the desired indicator in that site. For each indicator, a point spread
function (PSF) is calculated from the whole sky radiance maps generated
by a single source at sufficiently dense number of distances from the
observing site. If the PSF is transversally shift-invariant, i.e. if it
depends only on the relative position of source and observer, then we
can further speed up the map calculation via the use of fast
Fourier-transform (FFT). We present here examples of maps for different
indicators. Precise results can be calculated for any single site,
taking into account the site and light sources altitudes, by means of
specific inhomogeneous (spatially-variant) and anisotropic (non
rotationally symmetric) PSFs.