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Satellite oceanography: New results 6 page

The microwave surveillance conducted using ERS and RADARSAT satellite data are very useful for studying the variability of the White Sea ice because they are independence of night-time and weather. The ERS and RADARSAT data indicate that the ice cover in the White Sea has recently exceeded average long-term values. Practically the entire sea area proved to be covered with ice, with compactness of 9-10 points. Only individual regions of the sea surface remained free from ice, attributed to the specific features of the basin s hydrology and the wind effect upon the ice. The nature of new ice formation processes in various parts of the White Sea is also determined by the effects of tidal currents, which revealed them- selves very clearly in high-resolution SAR imagery. It has been shown that the effect of watering (moistening) of the ice edge by the tidal wave essentially changes the radar signal level. The study of the contrast of the ice-water boundary forms the basis of the SAR method of monitoring the intensity of tidal currents and registering the tidal phase shift. The distribution of drift ice and the configuration of the ice edge can provide an insight to the regional atmospheric circulation patterns. SAR imagery is capable of providing indirect evidence of an inflow of transformed Barents Sea waters of Atlantic origin to the White Sea Basin. In the Gorlo, some ice mosaic fields of thin first-year and young ice were shown to be suitable for the Greenland seal calving camps.

The SMMR and SSM/I data indicate some important changes that occurred in the sea ice concentration in the White Sea during November 1978 to December 1999. The observational data on the multi-frequency Tb is valuable for calculating the total sea ice concentration, providing therefore the information about the variability of the total ice extent in the White Sea. The NORSEX algorithm has been used to calculate the ice concentration from the SMMR and SSM/I Tb data. All data indicate an appreciable decrease in the total ice content with the lowest sea ice concentrations registered in 1992. A significant decrease in the ice concentration was established for all areas (e.g., -20% in Onezhskiy Bay and -4% in the Voronka). Starting from 1992, all regions of the White Sea show an opposite tendency (i.e., the ice concentration steadily increases). The obtained results


6.5

indicate that the rate of reduction of sea ice concentration constituted 8.1% per decade. The total surface area of the White Sea that was monitored was equal to 30,000 km2.

The White Sea is one of the most adequately studied areas in the Russian sector of the Arctic. Nevertheless, many essential problems concerning the winter hydrology require further studying (ice dynamics and ice exchange processes with the Barents Sea; the mechanism of generation of sub-ice currents and eddy structures and their spatial and temporal variations; the role of atmospheric processes and the phenomena occurring in the catchment in the variability of ice state characteristics; etc.).



The methods presented in this chapter, as well as the results obtained, constitute a solid basis for further utilization of remote sensing data (first and foremost, on the SST, concentration of chlorophyll-a, suspended matter, and ice cove) for calibration, tuning, and verification of numerical models. Ecosystem models can be further improved through the involvement of new approaches allowing for a quantitative assessment of primary productivity making use of remote sensing data. This will constitute a significant step forward in the perfection of system analysis methods intended for the estimation of the present status and prediction of changes in the marine environment in the future as a result of natural and anthropogenic forcing.


 


Date: 2016-03-03; view: 628


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