in the spectral ranges 0.3–1.0 mm which may be specified as the short-wave spectral
range. Solar radiation integrated with respect to the wavelength over the considered
spectral region will be called total radiation. Meanwhile, it should be noted that
further definitions of the radiation characteristics are not linked within this limitation
and could be used either for heat or for microwave ranges.
The notion of a monochromatic parallel beam (the plane electromagnetic wave
of one concrete wavelength and one strict direction) is widely used in optics for the
theoretical description of different processes. Usually solar radiation is set just in
that form to describe its interactions with different objects. The principle of an
independency of the monochromatic beams under their superposition is postulated,
i.e. the interaction of the radiation beams coming from different directions with the
object is considered as a sum of independent interactions along all directions. The
physical base of the independency principle is an incoherence of the natural
radiation sources.
1
This standard operation is naturally used for the radiation field, i.e. the consideration of it as a sum of non-interacted parallel monochromatic beams. Furthermore,
radiation energy can’t be attributed to a single beam, because if energy were finite
in the wavelength and direction intervals, it would be infinitesimal for the single
wavelength and for the single direction. For characterizing radiation, it is necessary
to pass from energy to its distribution over spectrum and directions.
Consider an emitting object (Fig. 1.1) implying not only the radiation source but
also an object reflecting and scattering external radiation. Pick out a surface element
dS, encircle the solid angle dO around the normal ~ r to the surface. Then radiation
energy would be proportional to the area dS, the solid angle dO, as well as to the
wavelength ranges [l, l + dl] and the time interval [t, t + dt]. The factor of
the proportionality of radiation energy to the values dS, dO, dl and dt would be
` n
J
dS 2
dS
` n
dW
r
dS
®
Fig. 1.1 The intensity and
the flux of radiation (radiance
and irradiance)
1 It should be noted that monochromatic radiation is impossible in principle. It follows from the
mathematical properties of the Fourier transformation: a spectrum consisting of one frequency is
possible only with the time-infinite signal. Furthermore, the principle of the independency is not
valid for the monochromatic beams because they always interfere. Both these contradictions are
possible to remove if we are considering monochromatic radiation not as a physical but as a
mathematical object, i.e. as a real radiation expansion into a sum (integral Fourier) of the harmonic
terms. The separate item of this expansion is interpreted as monochromatic radiation.
2
1 Radiation in the Earth Atmosphere
range. Solar radiation integrated with respect to the wavelength over the considered
spectral region will be called total radiation. Meanwhile, it should be noted that
further definitions of the radiation characteristics are not linked within this limitation
and could be used either for heat or for microwave ranges.
The notion of a monochromatic parallel beam (the plane electromagnetic wave
of one concrete wavelength and one strict direction) is widely used in optics for the
theoretical description of different processes. Usually solar radiation is set just in
that form to describe its interactions with different objects. The principle of an
independency of the monochromatic beams under their superposition is postulated,
i.e. the interaction of the radiation beams coming from different directions with the
object is considered as a sum of independent interactions along all directions. The
physical base of the independency principle is an incoherence of the natural
radiation sources.
1
This standard operation is naturally used for the radiation field, i.e. the consideration of it as a sum of non-interacted parallel monochromatic beams. Furthermore,
radiation energy can’t be attributed to a single beam, because if energy were finite
in the wavelength and direction intervals, it would be infinitesimal for the single
wavelength and for the single direction. For characterizing radiation, it is necessary
to pass from energy to its distribution over spectrum and directions.
Consider an emitting object (Fig. 1.1) implying not only the radiation source but
also an object reflecting and scattering external radiation. Pick out a surface element
dS, encircle the solid angle dO around the normal ~ r to the surface. Then radiation
energy would be proportional to the area dS, the solid angle dO, as well as to the
wavelength ranges [l, l + dl] and the time interval [t, t + dt]. The factor of
the proportionality of radiation energy to the values dS, dO, dl and dt would be
` n
J
dS 2
dS
` n
dW
r
dS
®
Fig. 1.1 The intensity and
the flux of radiation (radiance
and irradiance)
1 It should be noted that monochromatic radiation is impossible in principle. It follows from the
mathematical properties of the Fourier transformation: a spectrum consisting of one frequency is
possible only with the time-infinite signal. Furthermore, the principle of the independency is not
valid for the monochromatic beams because they always interfere. Both these contradictions are
possible to remove if we are considering monochromatic radiation not as a physical but as a
mathematical object, i.e. as a real radiation expansion into a sum (integral Fourier) of the harmonic
terms. The separate item of this expansion is interpreted as monochromatic radiation.
2
1 Radiation in the Earth Atmosphere