44
D.G. BARBER, A. THOMAS, AND T.N. PAPAKYRIAKOU
free and the grains are fairly small we do not expect any significant scattering (at 5.3
GHz) from the snow volume during this period.
Within first-year sea ice, microwave scattering appears to be dominated by a combination of basal layer volume scattering and ice surface scattering. During this period
we would expect to find a significant difference in solar noon versus solar midnight
observations, as small amounts of water in liquid phase would contribute to grain
growth and the elevated temperatures would significantly increase the brine volume of
the ice surface and snow basal layer. The overall magnitude of 0'0 will be dependent on
the ice surface microscale roughness and its surface brine volume.
Melt Onset. In multiyear sea ice, melt onset is denoted by a rapid decrease in 0'0. The
mechanism responsible is the absorption of microwave energy by the water in liquid
phase within the snow cover (Winebrenner et al. 1994) and by the presence of water in
liquid phase within the hummock structures free of a snow cover. An increase in permittivity and in particular an increase in tlIe dielectric loss effectively mask the volume scattering from the hummocks, thereby decreasing 0'0. The decrease in 0'0 proceeds
over both the pendular and funicular regimes of snow ablation.
In first-year sea ice, melt onset is denoted by a rapid increase in 0'0. There are two mechanisms which are likely candidates for tlIe observed increase. At relatively low water volumes (1-3%) the large, wet snow grains in tlIe basal layer may contribute a significant
volume scattering term to 0'0. As the water in liquid phase continues to increase (but is
maintained witlIin the pendular regime) it is likely that the snow surface may also contribute a surface scattering term to cro (Drinkwater 1989; Livingstone and Drinkwater
1991; Barber and LeDrew 1994). It most likely that the snow volume scattering term is the
dominant mechanism, since tlIe maximum cro reached at the first-year ice site was larger tlIan the corresponding one at tlIe multiyear ice site, even tlIough the snow surface
roughness was approximately equivalent between the two sites. A distinct dip in 0'0 at
the first-year ice site corresponded witlI tlIe transition from tlIe pendular and funicular
regimes. This transition marks the reduction of brine within tlIe basal layer to near zero,
an increase in the water in liquid phase at the base of tlIe snow cover and a reduction of
water in liquid phase in the top parts of tlIe snow volume (as tlIe surface begins to drain).
These processes could lead to a reduction of botlI the volume scattering and snow surface scattering hypothesized to dominate tlIe pendular regime conditions.
Advanced Melt. In multiyear sea ice, the advanced melt season is denoted by a rapid
increase in 0'0. As surface water forms in tlIe previous year's melt ponds tlIere is an
increase in the discontinuity at the air-water interface. The dielectric permittivity and
loss (E' and E") of this fresh water (which has a surface temperature of about +1 ·C) is
sufficiently large that we can expect a penetration depth on tlIe order of 1 cm (Ulaby et
al. 1986). We can expect an increase in scattering if the melt pond surfaces are windroughened. A reduction in the water in liquid phase within the hummocks may also
cause an increase in cro by increasing the volume scattering component of 0'0. Once the
ice surface begins to drain there is a pronounced decrease in the multiyear 0'0. This period coincides with a reduction in tlIe spatial extent of the melt ponds and cyclical
changes in the water in liquid content within the hummocks. The exact mechanisms
for scattering over multiyear sea ice in the advanced melt season remain largely unexplored and are identified here as a priority for future research.
In first year-sea ice 0'0 increases over the ponding period and decreases as the ice
begins to drain, analogous to that described for the multiyear ice surface. The mecha-
D.G. BARBER, A. THOMAS, AND T.N. PAPAKYRIAKOU
free and the grains are fairly small we do not expect any significant scattering (at 5.3
GHz) from the snow volume during this period.
Within first-year sea ice, microwave scattering appears to be dominated by a combination of basal layer volume scattering and ice surface scattering. During this period
we would expect to find a significant difference in solar noon versus solar midnight
observations, as small amounts of water in liquid phase would contribute to grain
growth and the elevated temperatures would significantly increase the brine volume of
the ice surface and snow basal layer. The overall magnitude of 0'0 will be dependent on
the ice surface microscale roughness and its surface brine volume.
Melt Onset. In multiyear sea ice, melt onset is denoted by a rapid decrease in 0'0. The
mechanism responsible is the absorption of microwave energy by the water in liquid
phase within the snow cover (Winebrenner et al. 1994) and by the presence of water in
liquid phase within the hummock structures free of a snow cover. An increase in permittivity and in particular an increase in tlIe dielectric loss effectively mask the volume scattering from the hummocks, thereby decreasing 0'0. The decrease in 0'0 proceeds
over both the pendular and funicular regimes of snow ablation.
In first-year sea ice, melt onset is denoted by a rapid increase in 0'0. There are two mechanisms which are likely candidates for tlIe observed increase. At relatively low water volumes (1-3%) the large, wet snow grains in tlIe basal layer may contribute a significant
volume scattering term to 0'0. As the water in liquid phase continues to increase (but is
maintained witlIin the pendular regime) it is likely that the snow surface may also contribute a surface scattering term to cro (Drinkwater 1989; Livingstone and Drinkwater
1991; Barber and LeDrew 1994). It most likely that the snow volume scattering term is the
dominant mechanism, since tlIe maximum cro reached at the first-year ice site was larger tlIan the corresponding one at tlIe multiyear ice site, even tlIough the snow surface
roughness was approximately equivalent between the two sites. A distinct dip in 0'0 at
the first-year ice site corresponded witlI tlIe transition from tlIe pendular and funicular
regimes. This transition marks the reduction of brine within tlIe basal layer to near zero,
an increase in the water in liquid phase at the base of tlIe snow cover and a reduction of
water in liquid phase in the top parts of tlIe snow volume (as tlIe surface begins to drain).
These processes could lead to a reduction of botlI the volume scattering and snow surface scattering hypothesized to dominate tlIe pendular regime conditions.
Advanced Melt. In multiyear sea ice, the advanced melt season is denoted by a rapid
increase in 0'0. As surface water forms in tlIe previous year's melt ponds tlIere is an
increase in the discontinuity at the air-water interface. The dielectric permittivity and
loss (E' and E") of this fresh water (which has a surface temperature of about +1 ·C) is
sufficiently large that we can expect a penetration depth on tlIe order of 1 cm (Ulaby et
al. 1986). We can expect an increase in scattering if the melt pond surfaces are windroughened. A reduction in the water in liquid phase within the hummocks may also
cause an increase in cro by increasing the volume scattering component of 0'0. Once the
ice surface begins to drain there is a pronounced decrease in the multiyear 0'0. This period coincides with a reduction in tlIe spatial extent of the melt ponds and cyclical
changes in the water in liquid content within the hummocks. The exact mechanisms
for scattering over multiyear sea ice in the advanced melt season remain largely unexplored and are identified here as a priority for future research.
In first year-sea ice 0'0 increases over the ponding period and decreases as the ice
begins to drain, analogous to that described for the multiyear ice surface. The mecha-