M.R. DRINKWATER
The most promising application of radar data in Antarctica is undoubtedly the ability to observe ice dynamics in time-sequential data sets. Further work to realize automated algorithms for processing these images to large-scale ice-kinematics products
will be undertaken in the near future, such that these data sets become widely available
to more general users of dynamic information. Ice-drift statistics alone are an important advance in understanding how the wind-aided advection of ice influences regional heat and freshwater budgets of the Southern Ocean.
Observation and recognition of particular ice characteristics and types is critical to
the interpretation and evaluation of new microwave image products in Antarctica. This
chapter provides the first broad picture of the backscatter characteristics or "signatures"
observed by C-band satellite radars, and serves as a foundation for a catalogue of Southern Ocean sea-ice signatures for regions in which in-situ measurements are frequently made. Examples illustrated in this study indicate that Antarctic ice can often look
considerably different from its Arctic counterpart, warranting future studies to expand
knowledge of its regional and seasonal variability. A caveat must be added, however, in
relationship to the utility of more general automated ice-classification schemes in
Antarctica, especially in regions and seasons where products cannot be characterized
in terms of their uncertainty. Indeed, the concept and requirement for proxy classes of
ice thickness should be revisited, and future algorithms to classify Antarctic ice should
be carefully crafted. Future schemes should utilize the present framework oflarge-scale
measurements by passive microwave and scatterometers, together with drawing upon
quantitative information derived from direct observations of the kinematics. Together these information sources provide the basis for a more valuable geophysical product than simply ice-type classification.
Coupled regional ocean-ice-atmosphere models will initially benefit from Southern
Ocean radar data through more accurate parameterizations of the ice rheology and
resulting motion and deformation fields. In turn, they will be used to evaluate the direct
relationships between the changing basin-wide distribution of sea ice and the flux of
momentum. Accurate monitoring of Southern Ocean ice formation, drift, deformation,
and divergence is of additional importance to indirect estimation of surface fluxes of
heat, freshwater and salt.
Mesoscale coverage of ERS-l and NSCAT can now be used together with the meteorological and oceanographic data to generate regional surface flux estimates in varying locations in the Southern Ocean. These are presently being compared with the
regional distribution of warm and cold water regimes observed in oceanographic data,
to map the spatial arrangement of ice surface flux environments in relation to the ocean
and atmospheric circulation patterns. Resultant estimates will be compared with simulated fluxes in one- and two-dimensional coupled sea-ice models to provide keys to
the principal sea-ice factors regulating the surface fluxes in ice-covered regions. Furthermore, the advantage of the coverage which the scatterometer image data provide
is to facilitate investigations oflinks between the Antarctic circumpolar wave and temporally varying attributes of the sea-ice cover. For the first time, high-resolution global coverage of sea ice enables teleconnections between mid- and high-latitude processes to be studied in Antarctica in a consistent fashion.
Acknowledgments. ERS-l data were supplied as part of the European Space Agencysupported A02.USA.1l9 project. Enhanced resolution ERS-l scatterometer data were
The most promising application of radar data in Antarctica is undoubtedly the ability to observe ice dynamics in time-sequential data sets. Further work to realize automated algorithms for processing these images to large-scale ice-kinematics products
will be undertaken in the near future, such that these data sets become widely available
to more general users of dynamic information. Ice-drift statistics alone are an important advance in understanding how the wind-aided advection of ice influences regional heat and freshwater budgets of the Southern Ocean.
Observation and recognition of particular ice characteristics and types is critical to
the interpretation and evaluation of new microwave image products in Antarctica. This
chapter provides the first broad picture of the backscatter characteristics or "signatures"
observed by C-band satellite radars, and serves as a foundation for a catalogue of Southern Ocean sea-ice signatures for regions in which in-situ measurements are frequently made. Examples illustrated in this study indicate that Antarctic ice can often look
considerably different from its Arctic counterpart, warranting future studies to expand
knowledge of its regional and seasonal variability. A caveat must be added, however, in
relationship to the utility of more general automated ice-classification schemes in
Antarctica, especially in regions and seasons where products cannot be characterized
in terms of their uncertainty. Indeed, the concept and requirement for proxy classes of
ice thickness should be revisited, and future algorithms to classify Antarctic ice should
be carefully crafted. Future schemes should utilize the present framework oflarge-scale
measurements by passive microwave and scatterometers, together with drawing upon
quantitative information derived from direct observations of the kinematics. Together these information sources provide the basis for a more valuable geophysical product than simply ice-type classification.
Coupled regional ocean-ice-atmosphere models will initially benefit from Southern
Ocean radar data through more accurate parameterizations of the ice rheology and
resulting motion and deformation fields. In turn, they will be used to evaluate the direct
relationships between the changing basin-wide distribution of sea ice and the flux of
momentum. Accurate monitoring of Southern Ocean ice formation, drift, deformation,
and divergence is of additional importance to indirect estimation of surface fluxes of
heat, freshwater and salt.
Mesoscale coverage of ERS-l and NSCAT can now be used together with the meteorological and oceanographic data to generate regional surface flux estimates in varying locations in the Southern Ocean. These are presently being compared with the
regional distribution of warm and cold water regimes observed in oceanographic data,
to map the spatial arrangement of ice surface flux environments in relation to the ocean
and atmospheric circulation patterns. Resultant estimates will be compared with simulated fluxes in one- and two-dimensional coupled sea-ice models to provide keys to
the principal sea-ice factors regulating the surface fluxes in ice-covered regions. Furthermore, the advantage of the coverage which the scatterometer image data provide
is to facilitate investigations oflinks between the Antarctic circumpolar wave and temporally varying attributes of the sea-ice cover. For the first time, high-resolution global coverage of sea ice enables teleconnections between mid- and high-latitude processes to be studied in Antarctica in a consistent fashion.
Acknowledgments. ERS-l data were supplied as part of the European Space Agencysupported A02.USA.1l9 project. Enhanced resolution ERS-l scatterometer data were