Degree of Master of

Analysis of the main methods applied

1. Comparative method: land use datasets

To begin with, the comparative method based on the analysis of the different land use datasets by Arcview program was the first in the exercise. The basic idea of this method was taking two land use maps, e.g. for 1970 and 1990 and comparison of the AALS water-surface areas for the respective years by using some special extensions of the Arcview program.
At first view, this method seemed quite simple and suitable for our exercise because it did not require a complicated procedure. But, in the process of GIS data mining, i.e. searching land use datasets for various time periods, we only managed to download the contemporary datasets (for 2004 and 2009). Therefore, the principal limitation of this method was the unavailability of the land use datasets for the 1970s and the 1980s.
Another limitation of the method was impossibility to examine dynamics of the AALS water surface changes during 1969-2009. In case of availability of the old land use datasets, we only could compare the AALS water-surface area for two years taken. Thus, we should conclude that this method does not detect the change dynamics of the water-surface area from year to year; it merely demonstrates the absolute value of the water-surface area in each year and indicates relative changes between two years. Summarizing, the major downsides of this method are:

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  unavailability of old land use datasets;
  
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  time-consuming process of the water surface calculation (in case of availability of old land use datasets);
  
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  impossibility to examine the change dynamics through the entire time line.
  

2. 
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   Comparative method: USSR military maps

Comparative method based on the analysis of the USSR military maps was the second method applied in the exercise. The principal idea of this method was similar to the first one,
i.e. analysis of the two USSR military maps concerning calculation of the AALS water- surface area. We should clarify that despite the supposed time consuming process of the calculation, the USSR military maps are considered to be more accurate with relation to demonstration of the AALS water-surface area in the various time periods. For this reason it was decided to try this method in the present research.
In order to demonstrate and make it and understandable for the reader, a part of the exercise procedure of the water-surface calculation is illustrated. Figure 7 shows some initial steps undertaken for the water-surface area calculation. The left picture displays the process of adjustment of the AALS represented on UUSR military map with the AALS on Google Earth. The right picture shows the next step, namely, image interpretation. After these two steps this method assumes working with annotated images in the Arcview program for the purpose of the water-surface area and volume calculation.
Notwithstanding the above, in the course of the work we encountered some serious limitations which forced us to reject this method. The main limitation we identified was the

Figure 7. Initial steps taken for the AALS calculation (screenshot from Google Earth)

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uncertainty of the creation time of the USSR maps. Specifically, some maps were created in 1975, but then were revised in 1985; others were composed in 1982 and revised in 1985. Consequently, it was impossible to calculate the AALS water-surface area precisely for a certain year and results obtained could be with low accuracy. For this reason this method was omitted.

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