ABSTRACT
The quality of solar radiation at the Earth's surface can vary with latitude and elevation, especially with respect to variation in amounts of ultraviolet radiation. The energy balance concept provides a theoretical basis for predicting the water use of well-watered crops. Information on the surface temperature of crop plants can be used to determine whether a crop needs to be irrigated. Empirical indexes have been developed for remotely quantifying the degree of stress experienced by crop canopies based on information obtained with scanners in aircraft or satellites. Consider a cropped area next to a body of water, such as a large lake, during the spring and summer. The energy balance over the water will result in less heating of the air during the day than occurs in the cropped area, because there will be more heat transfer into the water than there is into the soil under the cropped area.
