Geology Reference
In-Depth Information
12
12
May 6
May 6
May 9
May 9
10
10
8
8
6
6
4
4
2
2
0
0
2
50
150
250
350
0
2468 10 12
05
12.5
20
Density (kg/m
3
)
Average grain size (mm
2
)
Salinity (%
°
)
12
12
May 6
May 9
10
10
8
8
6
6
4
4
2
2
0
0
0
.005
.015
.025
2
2.5
3
3.5
.05
.15
.25
Modeled permittivity (
ϵ
′
)
Modeled loss (
ϵ
″
)
Brine volume fraction
Figure 7.41
Profiles of physical parameters in snow overlaying FY sea ice in Barrow Strait, central Arctic. The salin-
ity, density, and average snow grain size were measured from samples extracted at approximately solar noon on 6
and 9 May, 1993 while brine volume fraction, permittivity, and loss factor were calculated using models presented
in
Barber and Nghiem
[1999] (adapted from
Barber and Nghiem
[1999], Figure 2, with permission from AGU).
Table 7.7
Density of different snow types.
Snow type
New snow
Damp new snow
Settled snow
Depth hoar
Packed snow
Firn snow
Density (kg/m
3
)
50-70
100-200
200-300
100-300
350-400
700-800
7.7.3.1. Optical and Thermal Infrared Regions
In principle, discrimination between ice and water is pos-
sible from optical data (when solar light conditions are
appropriate) because there is enough contrast between the
albedo from the two objects. Albedo of seawater is usually
below 0.1, whereas albedo of bare ice surface varies between
0.5 and 0.6. The interest in using optical observations from
snow‐covered ice in the polar regions (particularly the
Arctic) is mainly for mapping the albedo and exploring
its seasonal and interannual variability (given the recent
decline of the ice extent in the Arctic). Snow over ice reveals
a wide range of albedo. It increases the surface albedo to
about 0.9 for fresh snow, but it drops to 0.5 or lower values
as the snow ages [
Grenfell and Maykut
, 1977]. When the
snow starts to melt, the albedo decreases to 0.4 or lower.
Because of this wide range of albedo from the snow, the
status of the snow on ice becomes important for determin-
ing the onset and the rate of ice melt (melting accelerates
when the albedo of the overlain snow is low). For that rea-
son many studies were launched to explore the effect of
physical properties of the snow on its optical behavior in
relation to the wavelength of the incident radiation. A com-
prehensive review on the subject is given in
Warren
[2012].
It demonstrates the dependence of albedo on the snow
grain size, wetness, impurity contents, and wavelength and
viewing angles of the radiation. Other details on optical
remote sensing of snow‐covered sea ice can be found in
Warren
[1982],
Zhou
[2002], and
Pedersen
[2007].
