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A COMPARATIVE TEST OF UNRESTRICTED, 
STRATIFTED, TWO-PHASE AND TWO-STAGE 
PPS TIMBER VOLUME SAMPLING USING 
AN ORTHOPHOTO MOSATC 
by 
\ * 
D.A. Stellingwerf 
General 
In this part are given the formulae which are used for the calculation of 
volumes and standard deviations of spruce plus fir as resulting from four 
different sampling methods carried out on a forest area of 10,000 hectares 
in Austria. 
The unrestricted random sampling 
Estimate of total volume: v,- A, xvx (plot area) (m°) 2:03 0.70. X4) 
t 
v 
= i 
Estimate of mean volume : v = BR (n5 /plot) 
MS 
n : number of plots in sample 
Vy : volume (a3) in plot i 
Ac : total conifer area (spruce + fir) (ha) 
y4- X | 
  
  
i 2 
Estimate of variance : S - 2 (Ac)  . . . . 00 + . . (2) 
(n-1) 
The stratified sampling 
T 
- 3 
Estimate of total volume : vr S. Pii (plot area) (m) . . . . . . .(3) 
n. 
J 
v 
= ij 3 
Estimate of mean volume per stratum j : vs de ra (m /plot) 
j 
  
*Ir D.A. Stellingwerf, Professor Forest Survey, Chairman Division of 
Natural Resources, Head Department of Forestry, International Institute 
for Aerial Survey and Earth Sciences, Enschede, The Netherlands.