Schardt, Mathias
number of stands | mean difference weighted top heights - h | Standard deviation of differences
Alpine test site | 139 - 0.3256 3.1259
hilly test site 49 - 0.9099 5.2412
both test sites 188 - 0.4949 5.0520
Table 3: Statistics for the assessment of tree heights
R Square | Std. Error of Estimation
Alpine test site | 0.633 3.9833
hilly test site 0.823 3.0045
both test sites | 0.715 3.8018
Table 4: Statistics for the fitted top height models
The following features were extracted for each stand from the maximum filtered laser data (max laser):
— arithmetic mean of the laser-derived tree heights (h)
— crown closure, assuming heights of more than 6 m to be crown hits (c)
The stand-wise average tree height values were compared with weighted top heights (one top height for different top
heights from different tree species within one stand) from forest inventory data. Table 3 depicts the statistics for each test
site alone and for both test sites together.
The assumed dependence on crown closure is shown in figure 4 for both test sites. In cases where the crown closure is
below 65 %, the laser-derived tree heights (h - from max laser) are significantly lower than the weighted top heights from
forest inventory. Hence, weighted top heights were predicted by laser-derived tree heights (h - from max laser) and crown
closure (c) for the Alpine test site 1, the hilly test site 2 and both test sites together 3
predicted top height = 16.16 4- 1.35 « h — 29.3«c (1)
predicted top height = 12.366 + 1.619 «xh — 31.889 x ¢ (2)
predicted top height = 15 -- 1.43* h — 29.5 «c (3)
Table 4 depicts the statistics for the fitted top height models and figure 5 shows the predicted top heights for both test sites
using equation 3.
Statistics show, that 72 % (R square 0.715) of forest inventory top heights can be predicted by laser-derived mean tree
heights and crown closure with the same model for different test site conditions concerning tree species mixture and
terrain. However, mean errors from forest floor model between 18 and 100 cm, deteriorating the tree-height map, have to
be considered. Assuming that forest floor DTMs can be improved (Ruppert et al., 2000), accuracy for laser-derived mean
tree heights cannot be stated as the final results in this study.
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1320 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.
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