Direct Solar Radiation Models by Formetta et al. 2012-2013

This paper presents two new modelling components based on the Object Modelling System v3 for the calculation of the shortwave incident radiation on complex topography settings, and the implementation of several ancillary tools. To understand it, it can be useful to give a look to the previous post on radiation of few weeks ago. The first component, NewAGE-SwRB, accounts for slope, aspect, shadow and the topographical information of the sites, and use suitable parametrisation for obtaining the cloudless irradiance. A second component, NewAGE-DEC-MOD's is implemented to estimate the irradiance reduction due to the presence of clouds, according to three parameterisations. To obtain a working modelling composition, suitable to be compared with ground data at measurement stations, the two components are connected to a Kriging component, and, with the use of a further component NewAGE-V (verification package), the performance of modeled is quantitatively evaluated. The two components (and the various parametrisations they contain) are tested using the data from three basins catchments, and some simple verification test is made to assess the goodness of the methods used. The components are part of a larger system, JGrass-NewAGE, their input and outputs are given as geometrical objects immediately visualisable in a GIS (for instance the companion uDig), and can be used seamlessly with the various modelling solutions available in JGrass-NewAGE for the estimation of long wave radiation, evapotranspiration, and snow melting, as well as stand-alone components to just estimate shortwave radiation for various uses. The modularity of the approach is shown to be extensible to more accurate physical-statistical studies aimed to assess in deep the components performances and to extend spatially their results, without the necessity of recoding any part of the component but just making use of connective scripts.

This is, obviously not the first effort in such direction, and some other good softwares were produced as 
SolarFlux (in ArcInfo GIS) (Dubayah and Paul, 1995; Hetrick et al., 1993), Solar Analyst (Fu and Rich, 2000), SRAD (by Moore, 1992, and documented in Wilson and Gallant, 2000- but you can see this), Solei (Miklanek, 1993 - see this) or r.sun (Hofierka and Suri, 2002), and often integrate the models in GIS. 
Our modelling, making treasure of these previous efforts, is also in line with those tools that try to respond to the increase demand of modularity and interchangeability in hydrological and biophysical models and have been developed in the last decades.

Executable, Data, and Documentation of the system can be found following this link (not yet operational - give me a little time for preparing it, with the objective that everyone can reproduce the results of the paper). Source code is partially available through the jgrasstool page.