150
M.R. DRINKWATER
ka.edu). The recent addition of RADARSAT with its tape-recording capacity has
increased the flexibility for recovering information in inaccessible locations such as
the Southern Oceans.
8.2.3
Scatterometer Imaging
The nonimaging wind scatterometer mode of the AMI on board ERS (EScat) enables
continuous radar coverage of Antarctica along a 500-km swath during the period when
the SAR is switched off. Low bit-rate EScat data (with an intrinsic resolution of approximately 50 km) do not require direct station transmission and are tape recorded and
downlinked to more accessible ESA ground stations (ESA Earthnet 1992). Scatterometer crO vv data can therefore be collected at times and in regions where direct SAR downlink is impossible. Extensive daily coverage of the ERS-1 scatterometer is particularly
valuable due to the lack of data reception in the AMI SAR mode when Antarctic receiving stations are closed. This is especially true in the Weddell Sea, because of the "campaign-style" operation of GARS and limited access to Syowa.
A method is proposed using data acquired in the EScat mode for mapping sea-ice
characteristics over the entire Southern Oceans ice cover. Recent advances in image generation from scatterometer data (Drinkwater et al.1993a) enable complementary,mediurn-scale resolution images to be generated from EScat orbital swath data. This method
allows construction of enhanced-resolution (approximately 20 km) scatterometer
images (with pixel spacing of 12-14 km) from the backscatter data record, and by virtue
of the wider swath and larger coverage allows mapping of the entire sea-ice cover in a
few days (Drinkwater et al. 1993a; Long et aI1993). The advantage of EScat image data
is that they form an uninterrupted sequence of C-band backscatter of Antarctic sea ice
from December 1991 onwards. Not only are these data critically necessary to fill in areas
of sparse temporal and spatial radar data coverage, but they are also complementary
to the restricted incidence angle data (20-26" incidence) of the SAR. The contrasting
20-60" incidence angle diversity of these C-band scatterometer data enables much
greater capability for discriminating ice types around Antarctica than by either SAR or
passive microwave alone. Coupled with higher frequency passive microwave and finer-resolution SAR, these data enable a better understanding of the time sequence and
seasonal history of Antarctic sea-ice formation, drift, deformation and decay.
8.3
Sampling Issues
8.3.1
Temporal and Spatial (overage
One of the priorities for scientific studies of polar ice and snow is high spatial and temporal coverage, due to the short times cales of variability in snow and ice conditions.
Exploitation of radar data, particularly in studies related to the mapping and monitoring of the sea-ice cover, was one of the main driving forces behind inclusion of the
SAR instrument on board ERS-l (Drinkwater 1995a). A large number of sea-ice studies are currently being performed using Arctic Ocean SAR data received at northern
M.R. DRINKWATER
ka.edu). The recent addition of RADARSAT with its tape-recording capacity has
increased the flexibility for recovering information in inaccessible locations such as
the Southern Oceans.
8.2.3
Scatterometer Imaging
The nonimaging wind scatterometer mode of the AMI on board ERS (EScat) enables
continuous radar coverage of Antarctica along a 500-km swath during the period when
the SAR is switched off. Low bit-rate EScat data (with an intrinsic resolution of approximately 50 km) do not require direct station transmission and are tape recorded and
downlinked to more accessible ESA ground stations (ESA Earthnet 1992). Scatterometer crO vv data can therefore be collected at times and in regions where direct SAR downlink is impossible. Extensive daily coverage of the ERS-1 scatterometer is particularly
valuable due to the lack of data reception in the AMI SAR mode when Antarctic receiving stations are closed. This is especially true in the Weddell Sea, because of the "campaign-style" operation of GARS and limited access to Syowa.
A method is proposed using data acquired in the EScat mode for mapping sea-ice
characteristics over the entire Southern Oceans ice cover. Recent advances in image generation from scatterometer data (Drinkwater et al.1993a) enable complementary,mediurn-scale resolution images to be generated from EScat orbital swath data. This method
allows construction of enhanced-resolution (approximately 20 km) scatterometer
images (with pixel spacing of 12-14 km) from the backscatter data record, and by virtue
of the wider swath and larger coverage allows mapping of the entire sea-ice cover in a
few days (Drinkwater et al. 1993a; Long et aI1993). The advantage of EScat image data
is that they form an uninterrupted sequence of C-band backscatter of Antarctic sea ice
from December 1991 onwards. Not only are these data critically necessary to fill in areas
of sparse temporal and spatial radar data coverage, but they are also complementary
to the restricted incidence angle data (20-26" incidence) of the SAR. The contrasting
20-60" incidence angle diversity of these C-band scatterometer data enables much
greater capability for discriminating ice types around Antarctica than by either SAR or
passive microwave alone. Coupled with higher frequency passive microwave and finer-resolution SAR, these data enable a better understanding of the time sequence and
seasonal history of Antarctic sea-ice formation, drift, deformation and decay.
8.3
Sampling Issues
8.3.1
Temporal and Spatial (overage
One of the priorities for scientific studies of polar ice and snow is high spatial and temporal coverage, due to the short times cales of variability in snow and ice conditions.
Exploitation of radar data, particularly in studies related to the mapping and monitoring of the sea-ice cover, was one of the main driving forces behind inclusion of the
SAR instrument on board ERS-l (Drinkwater 1995a). A large number of sea-ice studies are currently being performed using Arctic Ocean SAR data received at northern