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blue and green and generally decreases with wavelength,
although the data of Bukata et al. (1995) suggest an
increase in absorption in the red. In all cases, however,
absorption by suspended sediment, chlorophyll, or dis-
solved organic matter remains an order of magnitude less
than absorption by pure water. Scattering by dissolved
organic matter is insignificant, and the scattering cross-
section for chlorophyll is spectrally flat and considerably
smaller in magnitude than that for suspended sediment,
illustrated for four different materials in Figure 3.7b. The
radiative transfer modeling of (Legleiter et al., 2004, 2009)
demonstrated that higher concentrations of suspended
sediment produce greater scattering and increase the
volume reflectance of the water column, and thus
L
C
(
λ
), throughout the blue and green. As concentrations
increase, the range of wavelengths affected by these
scattering interactions extends farther into the red.
An important result of these studies is that the visible
spectrum can be partitioned, at least conceptually and for
a given set of conditions, into: 1) a scattering-dominated
regime at shorter wavelengths, where suspended sediment
concentration is a primary control on the water-leaving
radiance; and 2) an absorption-dominated regime, where
L
W
(
λ
) is mainly sensitive to variations in water depth due
Absorption
Scattering
0.3
3
1
0.01
Bukata et al.
Brown earth
Red clay
Sand
Chlorophyll
DOC
Pure water
0.2
2
0.5
0.005
0.1
1
0
80
0
0
80
0
400
500
600
700
400
500
600
700
Wavelength (nm)
Wavelength (nm)
(a)
(b)
Figure 3.7
Optical properties of the most important constituents of the water column. (a) The absorption spectrum of pure water is
plotted on the right vertical axis, based on the data of Pope and Fry (1997) from 400-720 nm and Smith and Baker (1981) from
730-800 nm. The absorption cross-sections for four different types of suspended sediment, chlorophyll, and dissolved organic carbon
(DOC) are plotted on the left vertical axis and are based on data compiled in the Hydrolight radiative transfer model (Mobley and
Sundman, 2001) and Equation (5.7) of Bukata et al. (1995) for DOC. (b) Scattering cross-sections for suspended sediment. Based on
data from Hydrolight (Mobley and Sundman, 2001).
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