Page 179 - Fluid Power Engineering

152 Chapter Eight

FIGURE 8-2 Illustration of a site with elevation contours, circle of radius r ,
72 radii emanating from the center and dark radial segments indicating
segments with slope greater than a threshold. (From Mortensen, N. G.,
Bowen, A. J., and Antoniou, I. Improving WAsP Predictions in (too) Complex
Terrain, EWEC, 2006.)

Ruggedness is a measure of the change in elevation or slope of
terrain. Quantitatively, ruggedness index (RIX) is defined as: Fraction
of terrain surface that is steeper than a critical slope θ c . There are three
parameters to computing RIX:

Calculation radius around a site center, normally a radius of

3.5 km is used
Critical slope, normally a value of θ c = 0.3 is used

Number of radii, normally 72 radii are used

Figure 8-2 illustrates the process of computing RIX; 72 radii are drawn
from the center and for each radius, segments are identified (darker
segments in the figure) with slopes above the critical slope. RIX is
calculated as the ratio of the sum of segment lengths to sum of the
radii. If 72 radii are used, then:

72
s
i=1 i
RIX = (8-7)
72r