Ice and Snow Regimes of the Volga River Reservoirs on the Base of Jason-1,2 Satellite Observations
Rybushkina, Galina; Troitskaya, Yuliya; Soustova, Irina
Institute of Applied Physics RAS, RUSSIAN FEDERATION
This work deals with the distinction of open water and ice/snow surface regimes for large and middle-sized freshwater inland waters, such as the Rybinsk and the Gorky reservoirs of the Volga River. It was shown earlier [1, 2] that the reprocessing of the Jason-1, 2 satellite data allow us to determine enough accurately the water level variations either for the large Rybinsk reservoir, or for the middle-sized Gorky reservoir. Ice and snow conditions of inland waters are of interest since they influence the life and economic activity if people and are significant indicators of climate changes. Satellite methods of ice-snow cover observations have certain advantages, connected with the global coverage, instantaneous observations of large water areas and relatively low cost. However, the use of satellite methods for inland waters is often difficult because of their spatial resolution comparable to or greater than the size of water reservoirs. Remote sensing with high spatial resolution is often associated with a large repeat period of data (ICESat), or with a significant dependence of the quality of data on weather conditions (Landsat). In this regard, the use of Jason -1, 2 satellites, equipped with a dual-frequency (13.6 GHz and 5 GHz) radar altimeters and a passive three-frequency (18, 21 and 37 GHz) microwave radiometers is of great interest, because the footprint diameter of their altimeters in Ku-band is about 10 Km and the repeat period of observations is ten days, that make them suitable for observations of large and medium-sized inland waters.
The method for ice-water discrimination was initially developed for the Topex/Poseidon data in  and was successfully applied to the Caspian, Aral and other Seas and Onega and Baikal Lakes [4,5]. This method is based on the joint analysis of the two parameters: the backscatter coefficient at 13.6 GHz and the average value of the brightness temperature values at 18 and 37 GHz and the conclusion about the ice cover can be made when these parameters exceed a certain threshold.
Open water and ice/snow regimes demonstrate two distinctive clusters on the two-dimensional histograms showing the backscatter coefficient in Ku band (13.6 GHz) versus the average value of brightness temperature at 18 and 37 GHz. This histograms allow also investigate the various phases of ice formation, ageing, snow accumulation and melting [3-5].
In this contribution we analyze the backscatter coefficient\brightness temperature histograms for the Rybinsk and Gorky reservoirs and explore the dynamics of the freezing and break-up cycles for this water bodies. Comparison with in situ observations is made and it is shown that the method works well for large water bodies such as the Rybinsk Reservoir and experience some difficulties for the middle-sized water bodies, such as the Gorky reservoir.
1 Yu.Troitskaya et al., "Satellite altimetry of inland water bodies," Water Resources, vol. 39(2), pp.184-199, 2012.
2. Yu.Troitskaya et al., "Adaptive retracking of Jason-1 altimetry data for inland waters: the example of the Gorky Reservoir", Int. J. Rem. Sens., vol. 33, pp. 7559-7578, 2012.
3. A. V. Kouraev, et al. Ice cover variability in the Caspian and Aral seas from active and passive satellite microwave data. Polar Research, vol. 22(1), pp. 43-50, 2003,.
4. A. V. Kouraev, et al. Observation of Lake Baikal ice from satellite altimetry and radiometry. Remote Sens. Environ., No. 108 , pp. 240 -253, 2007.
5. A. V. Kouraev, et al. Ice and snow cover of continental water bodies from simultaneous radar altimetry and radiometry observations. Surveys in Geophysics, vol. 29 (4-5), pp. 271-295, 2008.