Short wave transmisivity is estimated for broad-band considering an extended equation developed by Allen (1996), based from Majumdar et al.(1972), using coefficients developed by ASCE-EWRI (2005).
SWtrasmisivity(Kt = 1, ea, dem, incidence.hor)unitless turbidity coefficient 0<Kt<=1.0, where Kt=1.0 for clean air and Kt=0.5 for extremely turbid, dusty, or polluted air
near-surface vapor pressure (kPa)
digital elevation model
solar incidence angle, considering plain surface
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
Majumdar, N.; Mathur, B. & Kaushik, S. Prediction of direct solar radiation for low atmospheric turbidity Solar Energy, Elsevier, 1972, 13, 383-394
ASCE-EWRI The ASCE Standardized Reference Evapotranspiration Equation Report of the ASCE-EWRI Task Committee on Standardization of Reference Evapotranspiration, 2005
Other net radiation related functions: LAI,
METRICtopo, albedo,
incLWradiation,
incSWradiation, netRadiation,
outLWradiation, soilHeatFlux,
solarAngles,
surfaceTemperature