Geoscience Reference
In-Depth Information
Solar Radiation in the Atmosphere
1.1
Characteristics of the Radiation Field in the Atmosphere
In accordance with the contemporary conceptions, light (radiation) is an elec-
tromagnetic wave showing quantum properties. Thus, strictly speaking, the
processes of light propagation in the atmosphere should be described within
the ranges of electrodynamics and quantum mechanics. Nevertheless, it is
suitable to abstract from the electromagnetic nature of light to solve a number
of problems (including the problems described in this topic) and to consider
radiation as an energy flux. Light characteristics governed by energy are called
the radiative characteristics
.Thisapproachisusualforopticsbecausethefre-
quency of the electromagnetic waves within the optical ranges is huge and
the receiver registers only energy, received during many wave periods (not
a simultaneous value of the electro-magnetic intensity). The electromagnetic
nature of solar radiation including the property of the electromagnetic waves
to be transverse is bound up with the phenomenon of
polarization
,whichis
revealing in the relationship of the process of the interaction between radiation
and substance (refraction, scattering and reflection) and configuration of the
electric vector oscillations on a plane, which is normal to the wave propagation
direction. Further, we are using
the approximation of unpolarized radiation
.
The evaluation of the accuracy of this approximation will be discussed further
concerning the specific problems considered in this topic.
The followingmain types of radiation (and their energy) are distinguished in
radiation transferring throughout the atmosphere:
direct
radiation (radiation
coming to the point immediately from the Sun);
diffused solar
radiation (solar
radiation scattered in the atmosphere);
reflected solar
radiation from surface;
self-atmospheric
radiation (
heat atmospheric
radiation) and
self-surface
radi-
ation (
heat
radiation). The total combination of these radiations creates the
radiation field
in the Earth atmosphere, which is characterized with energy
of radiation coming from different directions within different spectral ranges.
As is seen from above, it is possible to divide all radiation into solar and self
(heat) radiation. In this topic, we are considering only solar radiation in the
spectral ranges 0.3−1.0
µ
m, where it is possible to neglect the energy of heat
radiation of the atmosphere and surface, comparing with solar energy. Further
with this spectral range we will be specifying
theshort-wavespectralrange.
Solar radiation integrated with respect to the wavelength over the considered
