"A CI. 
X. x4 pu p AP. T - rd "T A ci 4 'w Mw Sf qe AR A 
4.3 Slope Aspect 
À slope aspect can be expressed from DEM, 
which is one of the most important items for 
topographical analysis. In this study, the slope 
aspect shows along the maximum inclination angle 
at one target pixel. An index of slope aspect 
accuracy is also used percentages of correct pixels. 
In case of slope gradient accuracy, correct pixel 
means difference with verification slope gradient 
data indicates inside of 45 degree. Figure 9 shows 
relationship between contour line interval and 
correct percentage in each method. The correct 
percentage shows very lower than elevation or 
slope gradient, which is indicated less than 68%. 
However, buffering method is almost located the 
highest accuracy in all contour intervals. 
    
= 70-00: er 
i 0 o----Profile 
65.00 [Fr > --4l]-- Window 
| fg Buffering 
Correct percentage (% 
A C [91] eo 
aso 55 
e e e e 
© o eo o 
  
A 
o 
o 
o 
- 
L 
  
50 100 150 200. 250 30 3580 400 450 
Contour line interval (m) 
Figure 9 Relationship between contour line 
interval and correct percentage of slope aspect 
44 Stream Pattem 
A runoff analysis or a stream pattern 
generation is very popular application of DEM. 
Usually, such analysis can be carried out by using a 
grid series tank model. A precipitation is supplied 
to each DEM grid that is one of the tanks. An inlet 
content which means effective rainfall for 
discharge is calculated by following equation. 
Q,-KiR L? Qin: Inlet Content (n°) 
Ki: Infiltration 
R: Precipitation (m) 
L: Grid Size (m) 
The inlet content must discharge to next 
grid according to slope aspect and velocity. That 
is to say flow tracking. The slope aspect can be 
calculated from DEM, the velocity can be 
estimated from slope gradient which is also 
calculated from DEM. And the flow in the grid 
can be expressed by a continuous equation as 
follows; 
ps 3 
Q EC d. At Q: Remaining Content (ni ) 
HAL q in 4 m Qin: Inlet (ms) 
out: Outlet (m/s) 
At: Time (s) 
By using previous equations, stream pattern 
can be drawn. In this study, a parameter of 
infiltration was given 1.0, because purpose is just 
DEM evaluation. 
An index of stream pattern accuracy is also 
used percentages of correct pixels. In this case, 
correct pixel means difference with verification 
discharge value indicates inside of 20 m?/s. Figure 
10 shows relationship between contour line 
interval and correct percentage in each method. 
Buffering method is almost located high accuracy. 
However, in 400m contour interval, buffering 
method indicated the worst accuracy. The 
discharge accuracy is influenced by slope aspect. 
Though the slope aspect of buffering method kept 
the highest accuracy, stream pattern accuracy 
didn't keep it. This reason might come from 
difference of aspect distribution. 
   
   
65.00 .. 
to fo - = profile 
© -@---P 
p --Ja-- Window 
o * 
S 60.00 | —f— Buffering 
= 
D 
O 
I 
D 
ssl 
© 
© 
© 
O 5000 i : à j | : : 
  
  
100 150 200 250 300 350 400 
Contour line interval (m) 
Figure 10 Relationship between contour line interval 
and correct percentage of stream pattern 
4.5 Slope Stability 
A slope stability analysis is also popular 
application of DEM. Sometime we generate land 
slide risk map or slope failure risk map from DEM. 
The slope stability which means safety factor was 
Figure 11-b Illustration of 
Each Slice 
5 
    
  
   
  
Landslide 
  
    
Elevation 
  
C3 mi lee di m 
  
ritical Circle 
rs 
" 1 M 
Ie 
  
WP» Grid Si 
Length of Landslide nd ze 
Figure 11-a Illustration of Fellenius Method 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996