R. Perez et. al. developed a model for determining DNI from GHI as an improvement to the DISC model. This model, “DIRINT”, improves estimation by binning zenith angle, global horizontal transmittance, and dew point temperature; or various functions of these variables, including a time derivative of the global horizontal transmittance. Each parameterization or “bin” is indicative of the sky condition. The impact of each possible bin is given by finding a coefficient from a four-dimensional look-up table, and using this coefficient to modify the estimated DNI result from the DISC model. Perez et. al.’s paper “Dynamic Global-to-Direct Irradiance Conversion Models”, only names the DIRINT model as the “modified DISC” model (to distinguish from a “simple model” that was also introduced in the paper) and the name “DIRINT” must have been applied elsewhere.
The PV_LIB toolbox contains a function to perform the DIRINT model, called pvl_dirint.