F. CARSEY, R. HARDING, C. WALES
ance and hence its climate, the continental record of past climate changes, the history
of recent fault movements, and the evolution of the continental crust.
9.3
Applications of SAR in Sea Ice Research
Sea ice is important because of its roles in oceanic and atmospheric dynamics, oceanic productivity, and operations. In fact, sea ice and polar oceans studies are the primary motivation behind the RADARSAT program. At this time the central scientific issues
for the polar oceans are those relating to the interactions of the high-latitude seas with
the world ocean. These issues are: vertical mixing including oceanic convection and
shelf processes, freshwater fluxes in the form of ice, and ice-edge-driven dynamics such
as upwelling. Also of ongoing interest are the roles of ice in the radiation balance and
as a surface flux control in synoptic processes. Understanding these processes calls for
data on ice extent, motion, thickness, and concentration. SAR data are uniquely useful
in making these determinations on fine scales.
Scientifically, RADARSAT will contribute to a number of specific determinations. The
local and global heat and brine budgets are strongly influenced by the dynamics and
thermodynamics of polynyas and shelf processes in both the Arctic and the Antarctic,
and by the processes occurring during the melt season (Winebrenner et al. 1994). The
changes observed in the surface morphology of the ice pack resulting from deformation can be used to estimate changes in regional values for air-ice-ocean momentum
transfer, thereby contributing to the more effective utilization of such values in ice
dynamics models. Detailed observations of ice movement and deformation have
already stimulated the development of more realistic models of the rheology of sea ice
(Stern et al. 1995), and this should be extended for its variation with location, season,
ice thickness, and ice type. At the coastlines of ice-covered seas the interactions of ice
with land are important to the behavior of the ice pack itself and to processes such as
erosion and sediment transport in the near-shore region.
A key variable in polar seas is the simple matter of the presence of ice. C-band and
L-band SAR systems are generally able to resolve the ice edge to within a few hundred
meters. There are situations of ambiguity in this determination, notably when winds
roughen the sea adjacent to old ice or first-year ice rubble fields; this situation is the
largest source of error in the automatic determination of ice extent, and algorithms are
under development to correct that problem. At the ice edge forming ice can occur as
"grease ice" or "pancake ice;' and each of these has a unique backscatter level and
appearance in SAR data, although, again, algorithms for their automatic classification
are currently in development.
Ice type is an involved matter. The World Meteorological Organization recognized 13
stages of development of ice, including icebergs, and 12 forms of ice. Various scientists
have their own glossaries, often of subsets of the WMO list (WMO 1970). It is likely that
no system of observations, including in situ visual sighting, will produce a reliable classification of these stages and forms, but there have been efforts to accomplish a usable
classification of sea ice from satellite data, and these have met with various measures
of success (Carsey 1992). A common goal of these efforts is to successfully determine
the areal concentrations of areas of thin new ice (ice of less than about 50 cm thickness), thicker first-year ice (ice that has not been submitted to a summer melt period),
ance and hence its climate, the continental record of past climate changes, the history
of recent fault movements, and the evolution of the continental crust.
9.3
Applications of SAR in Sea Ice Research
Sea ice is important because of its roles in oceanic and atmospheric dynamics, oceanic productivity, and operations. In fact, sea ice and polar oceans studies are the primary motivation behind the RADARSAT program. At this time the central scientific issues
for the polar oceans are those relating to the interactions of the high-latitude seas with
the world ocean. These issues are: vertical mixing including oceanic convection and
shelf processes, freshwater fluxes in the form of ice, and ice-edge-driven dynamics such
as upwelling. Also of ongoing interest are the roles of ice in the radiation balance and
as a surface flux control in synoptic processes. Understanding these processes calls for
data on ice extent, motion, thickness, and concentration. SAR data are uniquely useful
in making these determinations on fine scales.
Scientifically, RADARSAT will contribute to a number of specific determinations. The
local and global heat and brine budgets are strongly influenced by the dynamics and
thermodynamics of polynyas and shelf processes in both the Arctic and the Antarctic,
and by the processes occurring during the melt season (Winebrenner et al. 1994). The
changes observed in the surface morphology of the ice pack resulting from deformation can be used to estimate changes in regional values for air-ice-ocean momentum
transfer, thereby contributing to the more effective utilization of such values in ice
dynamics models. Detailed observations of ice movement and deformation have
already stimulated the development of more realistic models of the rheology of sea ice
(Stern et al. 1995), and this should be extended for its variation with location, season,
ice thickness, and ice type. At the coastlines of ice-covered seas the interactions of ice
with land are important to the behavior of the ice pack itself and to processes such as
erosion and sediment transport in the near-shore region.
A key variable in polar seas is the simple matter of the presence of ice. C-band and
L-band SAR systems are generally able to resolve the ice edge to within a few hundred
meters. There are situations of ambiguity in this determination, notably when winds
roughen the sea adjacent to old ice or first-year ice rubble fields; this situation is the
largest source of error in the automatic determination of ice extent, and algorithms are
under development to correct that problem. At the ice edge forming ice can occur as
"grease ice" or "pancake ice;' and each of these has a unique backscatter level and
appearance in SAR data, although, again, algorithms for their automatic classification
are currently in development.
Ice type is an involved matter. The World Meteorological Organization recognized 13
stages of development of ice, including icebergs, and 12 forms of ice. Various scientists
have their own glossaries, often of subsets of the WMO list (WMO 1970). It is likely that
no system of observations, including in situ visual sighting, will produce a reliable classification of these stages and forms, but there have been efforts to accomplish a usable
classification of sea ice from satellite data, and these have met with various measures
of success (Carsey 1992). A common goal of these efforts is to successfully determine
the areal concentrations of areas of thin new ice (ice of less than about 50 cm thickness), thicker first-year ice (ice that has not been submitted to a summer melt period),