distance between the Sun and the Earth, and it is called a spectral solar constant.
Figure 1.3 illustrates the solar constant F 0 as a function of wavelength.
1.2 Interaction of the Radiation and Atmosphere
Consider a symbolic particle (a gas molecule, an aerosol particle) that is illuminated
by the parallel beam F 0 (Fig. 1.4). The process of the interaction of radiation and
this particle is assembled of the radiation scattering on the particle and of the
radiation absorption by the particle. Together these processes constitute the radiation extinction (the irradiance after interaction with the particle is attenuated by the
processes of scattering and absorption along the incident beam direction ~ r 0 ). Let
absorbed energy be equal to E a , scattered in all directions energy be equal to E s , and
total attenuated energy be equal to E e ¼ E a + E s . If the particle interacted with
F 0 , mW•cm -2 •mm -1
300
400
500
600
700
800
900
1000
40
80
120
160
200
240
Wavelength l, nm
Fig. 1.3 Spectral extraterrestrial solar flux
d W
r
j
F 0
g
®
Fig. 1.4 Definition of the
cross-section of the
interaction
1.2 Interaction of the Radiation and Atmosphere
7