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gray, and light), packed pancakes, FY ice, dry MY ice,
flooded MY ice, frozen melt pond, summer melting ice,
and summer frozen surface crust (which is an extreme
case). The data were compiled from 11 field and labora-
tory studies, all conducted before 1992. A subset of the
emissivity data published in Eppler et al . [1992] is pre-
sented in Table 8.10 for the OW and the three major ice
types (new, FY, and dry MY) at the three operational
frequencies of the space‐borne microwave radiometers.
It should be mentioned that other authors (e.g., Johannessen
et al ., 2007] presented slightly different values.
While the table shows an insignificant difference
between emissivity of OW and new ice, the difference
between emissivity of FY and MY ice is significant. All
ice concentration retrieval algorithms that use microwave
data are based on the emissivity contrast between OW on
one hand and FY ice and MY ice on the other hand.
Identification of new ice can be confused with OW. The
difference between ice and water emissivity is higher at
lower microwave frequencies and for the horizontal polar-
ization more than vertical polarization data. A frequently
used graph that shows the spectral microwave emissivity
of FY ice and OW is presented in Figure 8.30. Data were
obtained from experiments in the Bering Sea in the Arctic,
Weddell Sea in the Antacrctic, and Mould Bay, Northwest
Territories. The figure shows the significantly higher emis-
sivity of sea ice compared to seawater. The OW data were
obtained from leads and polynyas in the Arctic. Errors
associated with the emissivity of FY ice are attributed to
changes in snow cover while errors in the OW data are
mainly due to surface roughness. The data points shown
by solid circles are theoretical values of emissivity of OW
calculated using permittivity data presented in Stogryn
and Desargent [1985]. The strong bias of OW to the ver-
tical polarization is also obvious in Figure 8.30.
Spreen et al . [2008] calculated the emissivity from field
measurements of brightness temperature and presented
a graph showing frequency dependence of emissivity in
the microwave frequency (Figure 8.31). The winter data
of FY ice, MY ice, and OW were obtained during the
Norwegian Remote Sensing Experiment [ NORSEX
Group , 1983], and summer data were obtained from mea-
surements of mixed FY ice and MY ice in marginal ice
Table 8.10 Emissivity of major ice types and OW compiled
from an extensive data set published in studies before 1992.
18.7 GHz
37 GHz
90 GHz
Ice Type
H
V
H
V
H
V
OW
0.332
(0.018)
0.570
(0.033)
0.392
(0.015)
0.662
(0.029)
0.528
(0.022)
0.792
(0.019)
NEW
0.368
0.623
0.417
0.703
0.573
0.850
FY
0.888
(0.019)
0.941
(0.019)
0.913
(0.013)
0.955
(0.015)
0.886
(0.031)
0.926
(0.045)
MY
0.780
(0.080)
0.850
(0.068)
0.706
(0.115)
0.764
(0.079)
0.650
(0.011)
0.680
(0.105)
Note : Data are presented for the most commonly used
operational frequencies of passive microwave spaceborne
sensors. Numbers in parenthesis are standard deviations
[adapted from Eppler et al ., 1992].
1. 0
First-year ice
0.8
Vertical polarization (V-pol)
Horizontal polarization (H-pol)
Theory
Observation
0.6
Open water
0.4
0.2
1
10
100
Frequency, GHz
Figure 8.30 Variation of emissivity of FY ice and OW with microwave frequency. Data obtained from shipboard
and surface‐based radiometer at 50° incidence angle. Error bars represent variability in measurements. Emissivity
values were calculated from measured brightness temperatures. Solid circles are theoretical values obtained using
complex permittivity of calm and rough water surface [ Eppler et al ., 1992, Figure 4‐1, with permission from AGU].
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