Geoscience Reference
In-Depth Information
Visible
Violet 0.39
μ
m
Red 0.77
μ
m
X rays and
γ
rays
Ultraviolet
Near infrared
Far infrared
Radar, TV, Radio
10
−
3
10
−
2
10
−
1
1
10
100
1000
Thermal radiation
Figure 5.1
Spectrum of radiation with bands defined in terms of wavelength in
μ
m.
1.0
0.8
0.6
0.4
0.2
Figure 5.2
Normalized
spectra of shortwave and
longwave radiation.
0.0
0
1
Wavelength (mm)
10
100
range 3-100
m. The wavelength at which there is most energy in these two
spectra differs by a factor of about twenty and there is little overlap between them.
This fact is extremely important because it allows us to consider the two streams
of radiation separately.
μ
Blackbody radiation laws
The radiant flux density of a surface is defined to be the amount of radiant energy
integrated over all wavelengths emitted or received by unit area of surface per unit
time. In common with other energy fluxes, the flux of radiant energy is expressed
in units of W m
−2
. When describing radiation from natural surfaces it is simplest
first to consider the laws which describe radiation emitted from an idealized
emitting and absorbing surface called a
blackbody
, then to make corrections to
allow for the relative imperfections of real natural surfaces. A blackbody is an
ideal (standard) surface that emits maximum radiation at all wavelengths in all
