Self-Calibrating Method for Estimating Solar Radiation from Air Temperature

Abstract

Procedures are introduced for self-calibrating an equation for estimating solar radiation (R_s) in the absence of measurements. The self-calibration is based on computed clear sky solar radiation envelopes and uses daily maximum and minimum air temperature. The resulting calibration can predict both daily and monthly average R_s parameters in evapotranspiration equations. The method was tested at nine locations in the United States representing low, medium, and high elevations, semi-arid and subhumid climates and ocean locations and was generally accurate, especially when predicting monthly R_s. Prediction of daily R_s was less accurate, but was scattered evenly about the 1:1 relationships with measured R_s. The self-calibration procedure was about as accurate on a monthly basis as ratios of R_s to extraterrestrial radiation from regional stations. The self-calibration procedure was more accurate than fixed calibration coefficients. The method is both simple and conservative because it is constrained by computed clear-sky solar-radiation curves.