18
0
R
20 0
40
E
a: 60
w
I« 0
~
L!.
0
0
J:
I~ 20
0
40
60
Exercise 2
particulate materials suspended in the water. The scattering of light energy can be
viewed as a composite of reflection from a massive array of angles existing internally
within a lake or stream (Wetzel, 1983). The extent of scattering in a specific volume of
water varies greatly with the composition, quantity, and relative transparency of
suspended materials. Therefore, one would anticipate variations in scattering oflight in
relation to, for example, distribution of inorganic and organic suspended matter and
proximity to sediments.
Solar radiation in water is absorbed and dispersed by the processes discussed above.
Light attenuation is the reduction of radiant energy with depth by both scattering and
absorption mechanisms. The measurement of transmission or absorption of light in
water can be made in several ways. The percentage absorption through a given depth of
water may be expressed in percent according to the relationship developed by Birge
(1915, 1916):
100(10 - U
10
where 10 = irradiance at the surface of the lake or some discrete layer within the lake
and 1 z = irradiance at depth 2, usually taken at I-m intervals below 1 0 ,
The percentile absorption of pure water is very high in the infrared portion of the
spectrum and results in rapid heating of water by incident light. About 53 % of total
light energy is transformed into heat in the first meter of water. Absorption by pure
water decreases markedly in the shorter wavelengths to a minimum absorption in the
blue and increases again in the violet and ultraviolet spectral wavelengths (Fig. 2.1).
Solar irradiance 1 z at depth 2 is a function of the intensity at the surface, 1 0 , multiplied
by the antilog of the negative extinction coefficient (I]) at depth 2 in meters:
or
5
PERCENT AGE OF INCIDE NT LIGHT
In 10 - In 1 z = 1]2
Figure 2.1. Transmission of light by distilled water
at six wavelengths (R = red, 720 nm; 0 = orange,
620 nm; Y = yellow, 510 nm; G = green, 510 nm;
B = blue, 460 nm; V = violet, 390 nm). Percentage
of incident light that would remain after passing
through the indicated depths of water expressed on
linear (upper) and logarithmic (lower) scales. (Wetzel,
1983 after Clarke.)
0
R
20 0
40
E
a: 60
w
I« 0
~
L!.
0
0
J:
I~ 20
0
40
60
Exercise 2
particulate materials suspended in the water. The scattering of light energy can be
viewed as a composite of reflection from a massive array of angles existing internally
within a lake or stream (Wetzel, 1983). The extent of scattering in a specific volume of
water varies greatly with the composition, quantity, and relative transparency of
suspended materials. Therefore, one would anticipate variations in scattering oflight in
relation to, for example, distribution of inorganic and organic suspended matter and
proximity to sediments.
Solar radiation in water is absorbed and dispersed by the processes discussed above.
Light attenuation is the reduction of radiant energy with depth by both scattering and
absorption mechanisms. The measurement of transmission or absorption of light in
water can be made in several ways. The percentage absorption through a given depth of
water may be expressed in percent according to the relationship developed by Birge
(1915, 1916):
100(10 - U
10
where 10 = irradiance at the surface of the lake or some discrete layer within the lake
and 1 z = irradiance at depth 2, usually taken at I-m intervals below 1 0 ,
The percentile absorption of pure water is very high in the infrared portion of the
spectrum and results in rapid heating of water by incident light. About 53 % of total
light energy is transformed into heat in the first meter of water. Absorption by pure
water decreases markedly in the shorter wavelengths to a minimum absorption in the
blue and increases again in the violet and ultraviolet spectral wavelengths (Fig. 2.1).
Solar irradiance 1 z at depth 2 is a function of the intensity at the surface, 1 0 , multiplied
by the antilog of the negative extinction coefficient (I]) at depth 2 in meters:
or
5
PERCENT AGE OF INCIDE NT LIGHT
In 10 - In 1 z = 1]2
Figure 2.1. Transmission of light by distilled water
at six wavelengths (R = red, 720 nm; 0 = orange,
620 nm; Y = yellow, 510 nm; G = green, 510 nm;
B = blue, 460 nm; V = violet, 390 nm). Percentage
of incident light that would remain after passing
through the indicated depths of water expressed on
linear (upper) and logarithmic (lower) scales. (Wetzel,
1983 after Clarke.)