2
10
100
a
b
c
10 1
b
d
3
10
e
a
10 2
g
h
10 3
i
4
10
10 4
400
500
600
700
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Figure 15. Observed spectral transmittances for 1.5-
Figure 16. Spectral extinction coefficients for nine
m-thick first-year ice with a) 0.05-m snow cover plus
distinct cases: a) dry snow (Grenfell and Maykut
157 mg chlorophyll m2 biomass and b) 0.19 m snow
1977), b) ice below the eutectic point with solid salts
cover plus 117 mg chlorophyll m2.
present (Perovich and Grenfell 1981), c) melting snow
(Grenfell and Maykut 1977), d) surface scattering
layer of white ice (Grenfell and Maykut 1977), e) the
observations of extinction coefficient than of al-
interior of white ice (Grenfell and Maykut 1977), f)
bedo. Most of the reported sea ice spectral extinc-
cold blue ice (Grenfell and Maykut 1977), g) melting
tion coefficients have been calculated using a two-
blue ice (Grenfell and Maykut 1977), h) bubble-free
stream radiative transfer model (Grenfell and
fresh ice (Grenfell and Perovich 1981), and i) clear
Maykut 1977, Perovich and Grenfell 1981).
Arctic water (Smith and Baker 1981).
Figure 16 summarizes spectral extinction coef-
ficients culled from a number of sources for nine
distinct cases: dry snow, melting snow, ice below
spectral extinction coefficients are about 20 times
the eutectic point with solid salts present, the
larger than those of melting blue ice.
surface scattering layer of white ice, the interior
Coefficients in melting snow are above half
of white ice, cold blue ice, melting blue ice, bubble-
those in cold dry snow. Extinction coefficients for
free fresh ice, and clear Arctic water (Grenfell and
very cold ice below the eutectic point are quite
Maykut 1977, Perovich and Grenfell 1981, Smith
large, comparable to values for snow. In this case
and Baker 1981). The range of over one to two
solid salts precipitate in the interior of the sea ice.
orders of magnitude in the extinction coefficients
These precipitated salts are small and plentiful
shows the tremendous variation in attenuation
and, with an index of refraction of approximately
between different snow and ice types. Sea ice and
1.5, are effective scatterers. The drained surface
snow curves all show relatively constant values
layer of multiyear ice (white ice scattering) con-
in the 400- to 500-nm region, followed by strongly
tains an abundance of air inclusions which formed
increased attenuation at longer wavelengths.
as a result of brine drainage. These air inclusions
Again, as was the case for albedo, the magnitude
cause considerable scattering, and extinction co-
of the extinction coefficient is largely a function
efficients are large. In the interior of white ice
of the amount of scattering, while the wavelength
there are fewer air bubbles, and extinction coeffi-
dependence is determined by absorption. The
cients are correspondingly smaller. In the blue ice
greatest attenuation occurs in cold snow, where
cases the inclusions are primarily brine pockets,
13
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