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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012
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Figure 3. Scatter plot and fitted curve
After constructing the equation, those samples which have been
holding out (20 percent) were used for calculating bias and root
mean square error. Relative bias and RMSE were -5.8 and 49.8
percent, respectively (table 2).
Table 2. Bias, relative bias, RMSE and relative RMSE of stand
volume estimation
Bias (m^) -21.3
Relative Bias (%) -5.8
RMSE (m?) 183
Relative RMSE (%) 49.8
4. DISCUSSION
In the present research, a new approach for estimating forest
stand volume at plot level were presented and examined. It has
been found that the most proper pixel size for modelling stand
volume was 5 to 7 meter. Maybe, this is a consequence of this
fact that the average size of tree crowns at study area was
approximately 7 m. The smaller sizes contain some variation of
crown surface and larger sizes cause a smoothing in height
variation.
Many researches have been conducted for estimating stand
volume by remotely sensed data. When looking at accuracy
expressed as a relative RMSE of stand volume estimation, using
sattelite images, 45% (Mäkelä and Pekkarinen, 2004), 48% and
19% (Mäkelä and Pekkarinen, 2001), 51% (Labrecque et al.,
2006), 64% to 295% (Katila and Tomppo, 2001), 56% (Hyyppä
et al., 2000), 36% (Holmgren et al., 2000), 83% (Franco-Lopez
et al, 2001), 41% (Wallerman et al., 2002), 36% (Hall et al.,
2006) and using aerial photographs, 57.8% (Tuominen and
Pekkarinen, 2005), the present result is satisfactory.
Tuominen and Pekkarinen (2004) achieved 66.1% RMSE,
using modified colour-infrared aerial photographs and Sohrabi
(2008) using colour infrared aerial images of UltraCamD
reported 66.1 — 76.9 % RMSE at plot level. Here, we achieved
49.8% RMSE which is a good improvement in precision of
volume estimation of forest stands.
One big problem in this method occurs when trees canopy cover
Is totally closed. In this situation, the standard deviation of
height is low while stand volume is high. In future studies,
applying forest stratification could be studied.
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