Self-Calibrating Method for Estimating Solar Radiation from Air Temperature

Abstract

Procedures are introduced for self-calibrating an equation for estimating solar radiation (Rs) 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 Rs 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 Rs. Prediction of daily Rs was less accurate, but was scattered evenly about the 1:1 relationships with measured Rs. The self-calibration procedure was about as accurate on a monthly basis as ratios of Rs 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.