CHAPTER 1
Recent Advances in the Analysis of SAR Data
of the Polar Oceans
C. TSATSOULIS AND R. KWOK
Contents
1.1 Sea Ice and Climate
3
1.2 Synthetic Aperture Radar Remote Sensing of the Sea Ice Cover. . . . . . . . . . .
4
1.3 Analysis of Sea Ice SAR Data ........................................
5
1.4 This Book ........................................................
6
References
8
1.1
Sea Ice and Climate
Studies of the behavior of the world's sea ice cover are particularly important because
sea ice, with its associated snow cover, serves as an insulative layer separating the frigid
Arctic atmosphere from the relatively warm underlying ocean. In fact, the heat fluxes
through typical thick multiyear ice are two orders of magnitude less than fluxes
observed under equivalent meteorological conditions through newly formed ice leads.
Even though the areal coverage by thin ice is small (several percent) in the Arctic, the
integrated flux through this area would be comparable to that through thicker ice. The
presence of sea ice cover also changes the surface albedo from a value of 0.15 (for open
water) to 0.84 (dry snow on the surface of sea ice). Therefore, decreases in sea ice extent
and thickness caused by climatic warming would result in a pronounced positive feedback amplifying the observed change. A warming trend would be expected to result in
a decrease in the extent and thickness of sea ice, in turn causing further atmospheric
and oceanic warming and thus contributing to even further decreases. It is this sea ice
feedback that contributes to the increases in mean annual temperatures that have been
projected in simulations changes in global climate (Manabe and Stouffer 1980). In the
Greenland Sea, where Arctic sea ice exported through the Fram Strait encounters the
warmer North Atlantic water, there is net ice melt. It appears that deep convection - the
mixing of surface water with deep ocean water - in the Greenland and Iceland Seas is
conditioned by freshwater export from the Arctic Ocean. This melt process may be
important in maintaining the stratification of the ocean in this area, thus preventing
significant overturning (Aagaard and Carmack 1994). It was hypothesized that at some
level of increased export of ice, convection would cease; the northward transport of
Atlantic water would decrease; and the climatological ice cover would spread southward. Conversely, if the export were to decrease, a northward movement of the ice cover would be expected due to a weakening of the stratification in the Eurasian Basin.
Analysis of SAR Data of the Polar Oceans
Edited by C. Tsatsoulis and R. Kwok
© Springer-Verlag Berlin Heidelberg 1998
Recent Advances in the Analysis of SAR Data
of the Polar Oceans
C. TSATSOULIS AND R. KWOK
Contents
1.1 Sea Ice and Climate
3
1.2 Synthetic Aperture Radar Remote Sensing of the Sea Ice Cover. . . . . . . . . . .
4
1.3 Analysis of Sea Ice SAR Data ........................................
5
1.4 This Book ........................................................
6
References
8
1.1
Sea Ice and Climate
Studies of the behavior of the world's sea ice cover are particularly important because
sea ice, with its associated snow cover, serves as an insulative layer separating the frigid
Arctic atmosphere from the relatively warm underlying ocean. In fact, the heat fluxes
through typical thick multiyear ice are two orders of magnitude less than fluxes
observed under equivalent meteorological conditions through newly formed ice leads.
Even though the areal coverage by thin ice is small (several percent) in the Arctic, the
integrated flux through this area would be comparable to that through thicker ice. The
presence of sea ice cover also changes the surface albedo from a value of 0.15 (for open
water) to 0.84 (dry snow on the surface of sea ice). Therefore, decreases in sea ice extent
and thickness caused by climatic warming would result in a pronounced positive feedback amplifying the observed change. A warming trend would be expected to result in
a decrease in the extent and thickness of sea ice, in turn causing further atmospheric
and oceanic warming and thus contributing to even further decreases. It is this sea ice
feedback that contributes to the increases in mean annual temperatures that have been
projected in simulations changes in global climate (Manabe and Stouffer 1980). In the
Greenland Sea, where Arctic sea ice exported through the Fram Strait encounters the
warmer North Atlantic water, there is net ice melt. It appears that deep convection - the
mixing of surface water with deep ocean water - in the Greenland and Iceland Seas is
conditioned by freshwater export from the Arctic Ocean. This melt process may be
important in maintaining the stratification of the ocean in this area, thus preventing
significant overturning (Aagaard and Carmack 1994). It was hypothesized that at some
level of increased export of ice, convection would cease; the northward transport of
Atlantic water would decrease; and the climatological ice cover would spread southward. Conversely, if the export were to decrease, a northward movement of the ice cover would be expected due to a weakening of the stratification in the Eurasian Basin.
Analysis of SAR Data of the Polar Oceans
Edited by C. Tsatsoulis and R. Kwok
© Springer-Verlag Berlin Heidelberg 1998