Degree of Master of

Use of Digital Elevation Map (DEM)

The next method examined for the AALS water-surface calculation was based on the application of the Digital Elevation Map (DEM). The method assumed the following steps:

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  CEU eTD Collection
  Creation of the Digital Elevation Map (DEM) of the AALS by integration of the 6 Shuttle Radar Topographic Mission (SRTM) images in the Arcview program (Figure 8);
  
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  Working with the DEM map in Arcview program (Figure 9); the main idea here was to gradually fill the DEM of the AALS depression with water until the historic level of water table is reached; this level is defined by analyzing the old satellite images. Thus we could examine the water-surface area and volume of the AALS for the different years;
  
• 
  Comparison of the AALS water-surface in the Arcview program.
  

Figure 8. Integration of six SRTM images in the Arcview Program

Figure 9. Digital Elevation Map (DEM) created by Arcview Program

Relative to the previous two methods, this method is supposed to be more complicated in terms of technical skills needed for working in the Arcview program. In the process of using this method one crucial disadvantage, that brought us to reject this method, was identified. After the DEM creation it was revealed that the AALS depression on the DEM has been already filled with water, and consequently, the procedure of analyzing the AALS water- surface area depending on the different levels of water table was not possible. Consequently, this method was not suitable for our exercise as well as the previous two.

4. Remote sensing

The last method used for the present exercise was based on remote sensing assisted by the MultiSpec program. Among all methods described above, this method can be undoubtedly considered as the most sophisticated because:

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  It requires advanced technical skills in working with remote sensing needed, including reading of the special literature and tutorials;
  
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  It is extremely time-consuming method;
  
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  It is a combination of several software programs for the water-surface calculation.
  

Despite all complications, remote sensing was acknowledged to be very accurate and convenient method of the AALS water-surface calculation. To prove that, let us explain the main working steps taken here. They are:

• 
  
  CEU eTD Collection
  Downloading the AALS satellite images for the various time periods, starting from 1969 to 2009. There were two complications. One the one hand, not all satellite images were downloadable; for the exercise we managed to download the images for the following years: 1968, 1973, 1978, 1983, 1988, 1993, 1998, 2003, 2008 and 2009. But, at the same time, we should highlight that images obtained enabled to examine the change dynamics of the AALS water surface. On the other hand, process of satellite images preparation to remote sensing was time-consuming because several images consisted of two parts and they had to be integrated into one image (Figure 10);
  
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  Processing of the satellite images in the MultiSpec program; in total, 10 satellite images from the all given periods were processed;
  
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  Working with the processed satellite images in the Arcview program; Figure 11 shows the process of working with the image in the Arcview program, namely, calculation of the AALS water-surface area for 1993 by using a special Arcview extension called
  

Grid Analyst. The same procedure was conducted for all respective years considered in the exercise.

Figure 10. Preparation stage: integration of the satellite images






CEU eTD Collection
Figure 11. Working with the AALS processed image in the Arcview Program

3.