Radiation Properties of the Environment

We have already described the radiation spectrum of the sun and noted that the major portion of solar energy is concentrated in the short-wavelength region. It was also noted that as a consequence of this spectrum, real surfaces may exhibit substantially different absorption properties for solar radiation than for long-wavelength earthbound radiation. 

Meteorologists and hydrologists use the term insolation to describe the intensity of direct solar radiation incident on a horizontal surface per unit area and per unit time, designated with the symbol /. Although we shall emphasize other units, it will be helpful to mention a unit that appears in the meterological literature  

Insolation and radiation intensity are frequently expressed in langleys per unit time e.g., the Stefan-Boltzmann constant would be 

Reflection phenomena in the atmosphere occur for wavelengths less than the particle size and are fairly independent of wavelength in this region. The term albedo is used to describe the reflective properties of surfaces and is defined by 

The albedos of some natural surfaces are given in Table 8-4. The effect of solar incident angle on the albedo of water is shown in Fig. 8-64, where a is the angle which the incoming rays make with the horizontal. 

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