Structure and Properties of Lake Ice - Freezing of Lakes and the Evolution of their Ice Cover - page 78

Table 3.8 The bands of the electromagnetic radiation referred in lake research

Ultraviolet 100 - 400 nm UV-C 100 - 280 nm

UV-B 280 - 315 nm

UV-A 315 - 400 nm

Light a 380 - 750 nm Violet 380 - 450 nm

Blue 450 - 495 nm

Green 495 - 570 nm

Yellow 570 - 590 nm

Orange 590 - 620 nm

750 nm
Infrared 750 nm - 1 mm Near IR (IR-A) 750 - 1,400 nm
Short-wavelength IR (IR-B) 1.4 - 3 ʼ m
Thermal IR (IR-C) 3 - 15 ʼ m
Far IR 30 - 1,000 ʼ m
Microwaves 1 mm - 1 m Millimeter waves (MMW) 1 - 10 mm
Radar 1 - 30 cm
a Radiation visible to a human eye, also called ' visible light ' and ' optical band '

Red 620

-

In the derivation, it is assumed that ʻ k B T ≪ hc, which simpli es the Planck ' is law to

derive the direct solution.
The wavelengths from ultraviolet to microwaves are divided into bands as shown in
Table 3.8 . The limits are not sharp, and the reference transition wavelengths of the bands
show minor variability in literature. The solar spectrum peaks at 480 nm, has nearly all its
energy in the ultraviolet, light, and infrared (IR-A and IR-B) bands (Fig. 3.15 ). Narrow
Frauenhofer lines are seen in the short wave solar spectrum due to absorption by elements
in the solar atmosphere.
At the Earth s surface, the visible light distribution shows yellow to our eye, and UV-C

and most of UV-B are absent as absorbed by ozone in the upper atmosphere. According to
observations, even though the level of solar radiation varies largely due to atmospheric
conditions, the shape of the radiation spectrum is fairly stable. Atmospheric gases have
absorption bands, which show up in the spectrum, while cloudiness decreases the level of
radiation on the surface of the Earth. The radiation depends on the Earth

'

Sun distance r,
solar zenith angle Z and the attenuation in the atmosphere. This distance depends on the
time of year, and the solar zenith angle depends on the time of year and day and the
latitude, obtained from astronomical formulae (see Annex).
Semi-empirical equations are available for the clear sky atmospheric transmittance T tr
and the in

-

uence of cloudiness N. A general form for the incident solar radiation on a
horizontal unit area on the surface of the Earth is

fl