CHAPTER 7
Mapping the Progression of Melt Onset and Freeze-Up on
Arctic Sea Ice Using SAR and Scatterometry
D.P. WINEBRENNER, D.G. LONG, B. HOLT
Contents
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
7.2 Synopsis of Transition Date Mapping Using the ERS-l SAR . . . . . . . . . . .. 132
7.3 Enhanced-Resolution Scatterometer Observations of Freeze-Up ........ 138
7.4 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 142
References ................................................ 142
7.1
Introduction
The annual changes of seasons, their timing, and their variations from place to place
reflect and drive many processes of geophysical import, as well as a wide range of
human activities. In remote parts of the world, including the Arctic, knowledge and
understanding of annual and interannual cycles has been limited by a paucity of observational data. Satellite observations promise to illuminate many relationships and
underpin new theoretical understanding. Seasonal transitions on Arctic sea ice are
especially germane to studies of global climate and links between high latitude and
global geophysical processes.
For example, Scharfen et al. (1987) have reported evidence, based largely on satellite
observations, that the date when Arctic sea ice begins to melt is related to the areal extent
of sea ice remaining in late summer, which significantly affects global albedo (Ebert
and Curry 1993). It is widely thought that the length of the melt season, i.e., the number of days between spring melt onset and autumn freeze-up, strongly influences the
sea ice mass balance budget (Maykut and Untersteiner 1971; Ebert and Curry 1993),
which in turn influences global ocean circulation (Aagaard and Carmack 1994). Parkinson (1992), using satellite passive microwave data, has noted significant geographical
and interannual variability in melt season length. Carsey (1985) observed that Arctic
sea ice backscatter seemed to respond to the end of the melt season, i.e., the autumn
freeze-up, and that the progression of this event northward could be traced in the
record.
In all cases, however, the relevant satellite records are short, their analysis is to some
degree uncertain because of limited understanding of the physics underlying the
observations, and the necessary analysis was highly labor intensive and therefore slow
and limited. To realize the promise in satellite remote sensing, we must learn how to
Analysis of SAR Data of the Polar Oceans
Edited by C. Tsatsoulis and R. Kwok
© Springer-Verlag Berlin Heidelberg 1998
Mapping the Progression of Melt Onset and Freeze-Up on
Arctic Sea Ice Using SAR and Scatterometry
D.P. WINEBRENNER, D.G. LONG, B. HOLT
Contents
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
7.2 Synopsis of Transition Date Mapping Using the ERS-l SAR . . . . . . . . . . .. 132
7.3 Enhanced-Resolution Scatterometer Observations of Freeze-Up ........ 138
7.4 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 142
References ................................................ 142
7.1
Introduction
The annual changes of seasons, their timing, and their variations from place to place
reflect and drive many processes of geophysical import, as well as a wide range of
human activities. In remote parts of the world, including the Arctic, knowledge and
understanding of annual and interannual cycles has been limited by a paucity of observational data. Satellite observations promise to illuminate many relationships and
underpin new theoretical understanding. Seasonal transitions on Arctic sea ice are
especially germane to studies of global climate and links between high latitude and
global geophysical processes.
For example, Scharfen et al. (1987) have reported evidence, based largely on satellite
observations, that the date when Arctic sea ice begins to melt is related to the areal extent
of sea ice remaining in late summer, which significantly affects global albedo (Ebert
and Curry 1993). It is widely thought that the length of the melt season, i.e., the number of days between spring melt onset and autumn freeze-up, strongly influences the
sea ice mass balance budget (Maykut and Untersteiner 1971; Ebert and Curry 1993),
which in turn influences global ocean circulation (Aagaard and Carmack 1994). Parkinson (1992), using satellite passive microwave data, has noted significant geographical
and interannual variability in melt season length. Carsey (1985) observed that Arctic
sea ice backscatter seemed to respond to the end of the melt season, i.e., the autumn
freeze-up, and that the progression of this event northward could be traced in the
record.
In all cases, however, the relevant satellite records are short, their analysis is to some
degree uncertain because of limited understanding of the physics underlying the
observations, and the necessary analysis was highly labor intensive and therefore slow
and limited. To realize the promise in satellite remote sensing, we must learn how to
Analysis of SAR Data of the Polar Oceans
Edited by C. Tsatsoulis and R. Kwok
© Springer-Verlag Berlin Heidelberg 1998