International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
60m. Another, the terrain change is not clear according to
airborne and ground-based lidar data after earthquake (figure
3.14).
eC o A
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Sent Beat
omen
TEE SE |
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Figure 3.13. Five profiles of Jiu-fen-er landslide area
E E ET 630
f^ *
620 A
+
(W)uoneae13
o
e
[Profile]
5% 40: 29 mm 46° 90
Distance(M)
Figure 3.14. A profile of Jiu-fen-er landslide area according to
airborne and ground-based lidar.
3.3 Accuracy Evaluation of 3D Laser Scanning
The range accuracy of laser scanner is in millimeters as shown
by the manufacturers. In addition, the attitude of the scanners in
field operations is also key factor to the final accuracy (Lichti e/
al… 2000; RIEGL LMS GmbH, 2002). Besides, the natural
conditions and personnel capability are contributing to the
overall accuracy.
The accuracy of the test datasets obtained by airborne lidar in
Jiu-fen-er slide area is shown in Table 3.1 (Shih et al., 2002).
On basis of the 137 check points observed by RTK, RMS
accuracy of Opetch ALTM 2030 dataset is 10 cm, that of LH
ALS 40 is 12 cm. This result shows that accuracies varries with
terrain and landcover types.
Table 3.1. Terrain conditions for evaluation of the accuracy of
airborne lidar data of Jiu-fen-er area.
Area| # of Area Description Validation
points Category
Flat road surface
Average slope less than 10 degree,
A IS Road width 7 meters, open to the sky
Road width 5 meters, 5 to 30 meter Covered road
B 81 height difference between road and surface
road-side, sky visibility generally poor
à Slope ranges from 15 to 35 degrees, Cover-less,
C | 349 s
open to the sky, bare rock uniform slope,
nature bare rock
p | 169 Open to the sky, soft soil ARNO
E | 125 Slope about 10 degree, Orchid and Tea| Vegetated with
E field uniform height
F | 46 Slope about 30 degree, Tea field Tea Field
G | 82 Slope about 15 degree, Tea field Tea Field
Flat bare soil
H | 70 Slope about 10 degree, bare soil
As to the accuracy of ground-based laser scanner, Lichti
(2002) made observations by using I-SITE TLS ( Terrestrial
620
Laser Scanner) in a flat beige wall surface and setting for coarse,
medium, fine, ultra resolution and receiving multiple returns.
The range accuracy of the manufacturing specifications is *
25mm for high accuracy mode and £50mm for standard
accuracy mode. With 16 scans of each of 3 sets of 999
observation points, the bias was less than 0.05m. Thus, the
technique was used to observe a stringer bridge for observing
deformation after heavy overburdens.
The accuracy of applying ground-based laser scanner such as
ILRIS-3D has not been reported in an natural conditions of the
mountainous terrain in Taiwan. It is known that overall
accuracy is affected by the distance to the targets (RIEGL LMS
GmbH, 2002). Preliminarily, the results revealed by geodetic
control points on the slide surface observed both by EDM and
scanner is roughly around 1 cm (Figure 3.15)(Bureau of Soil
and Water Conservation, 2003).
For observing the topographic change in a time span, a
pre-requisite is to obtain datasets in accuracy better than the
variation of the topography. For Jiu-fen-er slide area, the
landslide is in very-large scale and the change is severe.
Therefore, all available datasets in this study are significant for
a preliminary evaluation despite the heterogeneous natures of
all the datasets. However, a further observation of the
deformation is in a micro topographic nature. The scale is in
centimeters. Ground-based lidar or permanent GPS stations
could be a suitable means for the deformation study.
Nus à
Ue MET
X: Pt. 234426.440, 2650337 897, 649.134
eV € PRR. FL lar
NE | Pt 234426451. 2650337882, 648.187
GPS-FA1 LasesF4-1 GPS-F5-1
Pt 234261 427, 2650255 734, 642.098 À Pt 234261.404, 2650255 752, 642 081 Pt. 234359.153. 2650298 900, 656,921
Figure 3.15. The coordinates of the control points by EDM and
Ground-based lidar of Jiu-fen-er slide area.
4. CONCLUSION
A geodetic transformed 3d model generated by merging
multiple laser scans on basis of properly distributed ground
control points is proved to be an important efficient source for
observing the topographic change of landslides in Taiwan.
Supplementary information can be resorted to existing 40m
DTM and the 5k photomaps. The earth quantities of fill-and-cut
of a landslide can be estimated by the DEM generated by
various approaches. Better accuracy can be achieved by
applying ground-based laser scanner.
Both ground-based or airborne laser scanner are not suitable for
evaluating erosion for that erosion processes are in a millimeter
scale. However, the change of the topography of landslides is in
a centimeter-to-meter scale. As proved in this study, significant
changes of landslide topography can be depicted in the results
by comparing the laser scanning datasets with those of other
sources.
The advantages of laser scanner are the efficiency of obtaining a
dataset with high density and high accuracy of 3D coordinates.
It is worthwhile to conduct further study on examining exact
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