11 The RADARSAT Geophysical Processor System
239
11.1.4
Open Water Fraction
During the melt season, fresh water is reinjected into the upper ocean. Meltwater
increases ocean stratification and therefore the heat flux between the ocean and atmosphere. The heating of the upper ocean also increases as the total ice concentration
decreases over the summer. Thus, the areal extent of open water is an important parameter to monitor for an understanding of the heat and mass balance of the ice cover.
After the onset of melt in the spring, the contrast between first-year and multiyear
ice at C-band is lost and there is at present no effective means for ice type classification
in the summer time. The summer sea ice cover at C-band has an average range of
backscatter that is between -17 dB and -12 dB. At C-VV, open water backscatter is dependent on wind speed and is typically higher than that of the ice cover if the wind speed
is above 4-5 m/s. The azimuthal look direction introduces only 1-2 dB modulation of
the backscatter at ERS-l100k angles. Comiso and Kwok (1996) used an algorithm which
takes advantage of the higher backscatter of wind-roughened open water relative to the
ice cover to estimate the open water fraction. In addition to the large range of incidence
angle in the RADARSAT data, the SAR is operated at C-HH. For use in the RGPS, this
algorithm needs to be modified to take advantage of the response of roughened water
at near range and the lower backscatter of open water at higher incidence angles at far
range.
11.1.S
Backscatter Histograms
The time-series evolution of backscatter contains information on the state of the surface of snow covered sea ice. It may be possible to link the conditions of the ice surface
to a variety of energy and mass fluxes based upon the state of ablation of the snow and
sea ice (Barber et al.I994). The RGPS will collect time series histograms of backscatter
within each Lagrangian cell to support investigations for relating the evolution of
backscatter to geophysically relevant parameters.
The intention of this chapter is to provide a description of the RGPS, the processing
algorithms, and the data products. In the next section, we outline the algorithms which
are implemented in the RGPS for analysis of the RADARSAT radar data. In Sect. 11.3,
the sea ice data products produced by the system are described. The implementation
of the system is discussed in Sect. 4. Summary remarks are provided in Sect. 11.5.
11.2
Sea Ice Algorithms
Ice motion and backscatter history are the two primary measurements made directly
from the time sequence of SAR imagery. The other sea ice parameters are derived from
the Lagrangian ice motion observations and backscatter record. The algorithms
described herein are strongly dependent on the availability of the time series of ice
motion, and estimation of some of these geophysical variables would not be feasible
without continuous observations of the ice cover. The specific details of the algorithms
described here can be found in the references in the text and elsewhere in this book
239
11.1.4
Open Water Fraction
During the melt season, fresh water is reinjected into the upper ocean. Meltwater
increases ocean stratification and therefore the heat flux between the ocean and atmosphere. The heating of the upper ocean also increases as the total ice concentration
decreases over the summer. Thus, the areal extent of open water is an important parameter to monitor for an understanding of the heat and mass balance of the ice cover.
After the onset of melt in the spring, the contrast between first-year and multiyear
ice at C-band is lost and there is at present no effective means for ice type classification
in the summer time. The summer sea ice cover at C-band has an average range of
backscatter that is between -17 dB and -12 dB. At C-VV, open water backscatter is dependent on wind speed and is typically higher than that of the ice cover if the wind speed
is above 4-5 m/s. The azimuthal look direction introduces only 1-2 dB modulation of
the backscatter at ERS-l100k angles. Comiso and Kwok (1996) used an algorithm which
takes advantage of the higher backscatter of wind-roughened open water relative to the
ice cover to estimate the open water fraction. In addition to the large range of incidence
angle in the RADARSAT data, the SAR is operated at C-HH. For use in the RGPS, this
algorithm needs to be modified to take advantage of the response of roughened water
at near range and the lower backscatter of open water at higher incidence angles at far
range.
11.1.S
Backscatter Histograms
The time-series evolution of backscatter contains information on the state of the surface of snow covered sea ice. It may be possible to link the conditions of the ice surface
to a variety of energy and mass fluxes based upon the state of ablation of the snow and
sea ice (Barber et al.I994). The RGPS will collect time series histograms of backscatter
within each Lagrangian cell to support investigations for relating the evolution of
backscatter to geophysically relevant parameters.
The intention of this chapter is to provide a description of the RGPS, the processing
algorithms, and the data products. In the next section, we outline the algorithms which
are implemented in the RGPS for analysis of the RADARSAT radar data. In Sect. 11.3,
the sea ice data products produced by the system are described. The implementation
of the system is discussed in Sect. 4. Summary remarks are provided in Sect. 11.5.
11.2
Sea Ice Algorithms
Ice motion and backscatter history are the two primary measurements made directly
from the time sequence of SAR imagery. The other sea ice parameters are derived from
the Lagrangian ice motion observations and backscatter record. The algorithms
described herein are strongly dependent on the availability of the time series of ice
motion, and estimation of some of these geophysical variables would not be feasible
without continuous observations of the ice cover. The specific details of the algorithms
described here can be found in the references in the text and elsewhere in this book