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D.P. WINEBRENNER, D.G. LONG, B. HOLT
7.4
Future Work
Clearly much work on, and involving, automated mapping of seasonal transitions on
sea ice remains to be done as of this writing. Methods and observations to date are no
more than prototypes; neither mature technology nor geophysically useful data sets yet
exist.
We believe the single most pressing need, from both a geophysical and an algorithmdevelopment standpoint, is for observational studies outside the popular Beaufort Sea
region. There is evidence that SAR signatures of sea ice vary significantly across the
Arctic basin, and the adjustment of algorithm parameters or entire algorithms may
prove necessary in the face of wider observations. From a geophysical standpoint, it is
Arctic-basin-scale variations in melt onset and freeze-up timing and melt season
length that are of most interest. We hope that data records now available from ERS-land -2-receiving stations in addition to the Alaska SAR facility can be used to address
this need.
As we have shown in the previous section, scatterometer data and backscattering
observations at 13-15 GHz hold considerable promise for extending seasonal transition
mapping. However, the physics of the relevant phenomenology, especially strong winter backscattering from first-year ice, is not well understood. We cannot say how broadly, in a geographical sense, higher frequency data may be useful without a better understanding of why the phenomenon arises, and therefore when, if ever, it is likely not to
arise. A physical understanding of backscattering also aids the multiple-incidence
angle processing necessary in constructing enhanced resolution scatterometer
imagery and ScanSAR imagery (e.g., RADARSAT).
Finally, from a purely geophysical standpoint, seasonal transition dates have been
mapped so far, by whatever means, for very few years in the Arctic. Progress on questions about the role of the Arctic in global climate and possible climate change cannot
be addressed without decadal and multidecadal time series. We therefore hope that the
next few years will bring the publication and availability of such time series. We believe
that with such availability, the role of automated interpretation of satellite observations
investigating polar geophysical questions will be greatly strengthened.
References
Aagaard K, Carmack EC (1994) The Arctic Ocean and climate: a perspective.AGU Geophys Monogr 85
Barber DG, LeDrew EF, Flett DG, Shokr M, Falkingham J (1992) Seasonal and diurnal
variations in SAR signatures of landfast sea ice. IEEE Trans Geosci Remote Sens 30,
no 3: 638-642
Beaven SG, Gogineni SP (1994) Shipborne radar backscatter measurements from Arctic sea ice during the fall freeze-up. Remote Sens Rev 9: 3-25
Carlstrom A, Ulander LMH (1993) C-band backscatter signatures of old sea ice in the
central Arctic during freeze-up. IEEE Trans Geosci Remote Sens 31, no 4: 819-829
Carsey F (1985) Summer Arctic sea ice character from satellite microwave data. J Geophys Res 90, no C3: 5015-5034
D.P. WINEBRENNER, D.G. LONG, B. HOLT
7.4
Future Work
Clearly much work on, and involving, automated mapping of seasonal transitions on
sea ice remains to be done as of this writing. Methods and observations to date are no
more than prototypes; neither mature technology nor geophysically useful data sets yet
exist.
We believe the single most pressing need, from both a geophysical and an algorithmdevelopment standpoint, is for observational studies outside the popular Beaufort Sea
region. There is evidence that SAR signatures of sea ice vary significantly across the
Arctic basin, and the adjustment of algorithm parameters or entire algorithms may
prove necessary in the face of wider observations. From a geophysical standpoint, it is
Arctic-basin-scale variations in melt onset and freeze-up timing and melt season
length that are of most interest. We hope that data records now available from ERS-land -2-receiving stations in addition to the Alaska SAR facility can be used to address
this need.
As we have shown in the previous section, scatterometer data and backscattering
observations at 13-15 GHz hold considerable promise for extending seasonal transition
mapping. However, the physics of the relevant phenomenology, especially strong winter backscattering from first-year ice, is not well understood. We cannot say how broadly, in a geographical sense, higher frequency data may be useful without a better understanding of why the phenomenon arises, and therefore when, if ever, it is likely not to
arise. A physical understanding of backscattering also aids the multiple-incidence
angle processing necessary in constructing enhanced resolution scatterometer
imagery and ScanSAR imagery (e.g., RADARSAT).
Finally, from a purely geophysical standpoint, seasonal transition dates have been
mapped so far, by whatever means, for very few years in the Arctic. Progress on questions about the role of the Arctic in global climate and possible climate change cannot
be addressed without decadal and multidecadal time series. We therefore hope that the
next few years will bring the publication and availability of such time series. We believe
that with such availability, the role of automated interpretation of satellite observations
investigating polar geophysical questions will be greatly strengthened.
References
Aagaard K, Carmack EC (1994) The Arctic Ocean and climate: a perspective.AGU Geophys Monogr 85
Barber DG, LeDrew EF, Flett DG, Shokr M, Falkingham J (1992) Seasonal and diurnal
variations in SAR signatures of landfast sea ice. IEEE Trans Geosci Remote Sens 30,
no 3: 638-642
Beaven SG, Gogineni SP (1994) Shipborne radar backscatter measurements from Arctic sea ice during the fall freeze-up. Remote Sens Rev 9: 3-25
Carlstrom A, Ulander LMH (1993) C-band backscatter signatures of old sea ice in the
central Arctic during freeze-up. IEEE Trans Geosci Remote Sens 31, no 4: 819-829
Carsey F (1985) Summer Arctic sea ice character from satellite microwave data. J Geophys Res 90, no C3: 5015-5034