Hourly estimation of net radiation over grass

Net radiation (Rn) is the main factor affecting the estimation of reference evapotranspiration (ETo) rates, and accurate Rn values are needed to provide good data. Rn can be measured; however, approximately half of the cost of maintenance for the California automated network was used for Rn sensors. Consequently, it was decided to remove the sensors and to estimate Rn from solar radiation (Rs), air temperature (T), and relative humidity (Dong et al., 1992).