Metadata, aspect and slope maps are combined to estimate solar angles for the entire image.
solarAngles(surface.model, MTL, WeatherStation)rasterStack with DEM, Slope and Aspect. See surface.model()
Landsat Metadata File
Weather Station data
Narrowband transmittances,are calculated considering some radiation transfer models operated over a wide range of climates and locations across the world, this parameter vary with the cosine of the solar angle, atmospheric pressure and precipitable water vapor in the atmosphere, so the author must obtain accurate values of these three parameters.
R. G. Allen, M. Tasumi, and R. Trezza, "Satellite-based energy balance for mapping evapotranspiration with internalized calibration (METRIC) - Model" Journal of Irrigation and Drainage Engineering, vol. 133, p. 380, 2007
Other net radiation related functions: LAI,
METRICtopo, SWtrasmisivity,
albedo, incLWradiation,
incSWradiation, netRadiation,
outLWradiation, soilHeatFlux,
surfaceTemperature