Figure 1. A three-dimensional plot presenting a section of the DEM, the ponds located within it along with their drainage basins. 
by the two methods is presented in Figure 2. 
In Figure 3, the differences in pond area determined 
using the two methods is presented. 
  
0.5 4 
04 4 
0.3 + 
02 4 
Pond area (DEM) 
  
3 ° 
0 + + + + 3 + ES 
0.4 0.6 0.8 1 1.2 1.4 
Pond area (aerial photographs) 
  
  
  
Figure 2. A plot of the pond areas (ha) derived from the two 
methods. n=30, r=0.263. 
The influence of the method on the estimation of the 
areas of the ponds was analyzed using a Student's t- 
test. The paired sample t-test gave a t-value of 9.77,- 
which resulted in a rejection of the Ho hypothesis (u 
aerial photographs = HDEM) at the 99% confidence 
level. 
820 
  
Frequency 
  
  
-1.5 
-1.2 -0.9 -0.6 -0.3 0 0.3 0.6 0.9 
  
Differences in pond area (aerial photographs-DEM) 
  
  
Figure 3. The differences in pond area (ha) determined using the 
two methods. mean=0.59, n=30. 
The correlation coefficient between the areas of the 30 
drainage basins to the ponds derived by the two 
methods (DEM and aerial photographs) was -0.059 
With a 95% confidence interval between -0.410 and 
0.308. A plot between the areas derived from the two 
methods is presented in Figure 4. 
In Figure 5, the differences in drainage basin area 
derived from the two methods is presented.