Porres, Maru 
  
the 2 2 2 2 
he Anc LIBI. p, a LL Ur t2pas t q't) 
el e M. 3 i2 
|o» *tq' Nü* p^ *q | L *9^ Nt p^-rg*3 | 
ater 
is to where, 
fter ira rat 3. 
sion 
Considering a tt x tt neighbourhood: 
fter w-(tt-1)/2 d 
atic for i=w,m-w do begin 
for j =w,n-w do begin 
vere for ss =-w,w do begin 
r(j,i)-(a(j-w,itss)*a(j*w,i*ss)-a(j-(w-1),i*ss)-a(j*(w-1),i*ss))*r(j,i) 
t(j,i)-(a(j*ss,i-w)*a(j*ss,i--w)-a(j*ss.i-(w-1))-a(j*ss,i*(w-1)))*t(j,i) 
end 
ge (aG * w,i- w)-*aG- w,i* w) t ai -(w -D,i -(w- D) t aG-* (w-D),i* (w-1) -aG- wi- w)-a(- w,i * w)-a(-* (w - 1i -(w - D) - a -(w - Di - (w - 0) 
; 4*(t-2)* d2 
: ou 
^o t#*(t-2)*(d?) 
14 t(], 1) 
(I) 2 —————— 
s of à tt* (tt -2)* (d?) 
ting 
end 
end 
dn From the curvature profile and curvature area images it is possible to obtain a third image H, calculated as the average 
of the other two (Florinsky & Kuryakova, 1996): 
k, +k, 
2 
With the topographic parameters defined and stored in images of equal grid size, number of rows and columns and with 
the same geographic reference, a single image called the multivariable digital model (Felicisimo,1994) is created, in 
which each of the bands corresponds to each of the topographic characteristics calculated above. To this multivariable 
model can be added some more bands such as the potential solar radiation and the normalised vegetation indices. 
  
Hz 
3.22. Calculation of the upslope catchment area. One of the factors that, together with the slope, the orientation and 
the curvature, defines the terrain is a map indicating the water accumulation potential of each point. This stores for 
each point the number of other points on the map from which water would drain to that point. To calculate this 
parameter it is first necessary to produce a map of flow directions; a possibility offered by the Arcview Spatial Analysis 
program. 
The values represented in a flow direction map are eight numbers each corresponding to the eight directions that the 
water could flow into adjacent cells. The direction of the water flow is determined by comparing the elevation of the 
pixel with its eight immediate neighbours.. 
The directions are: 
E —1 W -—16 
SE 2 NW — 32 
S 4A N 64 
SW — 8 NE —128 
Once the direction map has been calculated it is possible to define the accumulated areas as a function of the eight 
direction values. Thus the cells with the highest values are the areas which collect water draining from other cells and 
the areas with 0 value correspond to elevated areas which drain into the neighbouring pixels. These pixels are found on 
the watersheds and can be used to delineate the drainage basins. 
The calculation of the catchment specific area does not consider either evapotranspiration or infiltration of the water 
into the ground although it is still useful for showing the places where water could accumulate, areas which due to their 
greater humidity, a priori, favour regenerative processes, especially in areas like the study area where the lack of water 
is a determining factor in the characterisation of vegetation species. 
ble 
Ire 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 1173