  Methods to map artificial night sky brightness and stellar visibility across
large territories or their distribution over the entire sky at any site are
based on the computation of the propagation of light pollution with Garstang
models, a simplified solution of the radiative transfer problem in the
atmosphere which allows a fast computation by reducing it to a ray-tracing
approach. We present here up-to-date Extended Garstang Models (EGM) which
provide a more general numerical solution for the radiative transfer problem
applied to the propagation of light pollution in the atmosphere. We also
present the LPTRAN software package, an application of EGM to high-resolution
DMSP-OLS satellite measurements of artificial light emissions and to GTOPO30
digital elevation data, which provides an up-to-date method to predict the
artificial brightness distribution of the night sky at any site in the World at
any visible wavelength for a broad range of atmospheric situations and the
artificial radiation density in the atmosphere across the territory. EGM
account for (i) multiple scattering, (ii) wavelength from 250 nm to infrared,
(iii) Earth curvature and its screening effects, (iv) sites and sources
elevation, (v) many kinds of atmosphere with the possibility of custom setup
(e.g. including thermal inversion layers), (vi) mix of different boundary layer
aerosols and tropospheric aerosols, with the possibility of custom setup, (vii)
up to 5 aerosol layers in upper atmosphere including fresh and aged volcanic
dust and meteoric dust, (viii) variations of the scattering phase function with
elevation, (ix) continuum and line gas absorption from many species, ozone
included, (x) up to 5 cloud layers, (xi) wavelength dependant bidirectional
reflectance of the ground surface from NASA/MODIS satellites, main models or
custom data (snow included), (xii) geographically variable upward light
emission function.
