The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008
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coordinates by adding the effect ei and e 2 , the calibrated point
coordinates were shown in Table 5.
No.
1
2
3
4
5
X(mm)
1701.6
1698.5
1695.4
1692.4
1689.4
Y(mra)
-37911.6
-33929.9
-29978.3
-26057.9
-22163.6
Z(mm)
-213991.2
-213924.7
-213847.9
-213778.5
-213705.5
6
7
8
9
10
11
1686.4
1683.4
1680.5
1677.6
1674.7
1671.8
-18295.9
-14446.9
-10619.4
-6807.7
-3010.4
774.5
-213647.4
-213568.6
-213507.9
-213439.8
-213372.2
-213314.4
12
13
14
15
16
17
1668.9
1666
1663.2
1660.3
1657.5
1654.7
4550.6
8319.2
12082.6
15843.6
19604
23366.9
-213241.7
-213171.4
-213113.6
-213047.8
-212975.2
-212917.1
18
19
20
21
22
23
1651.8
1649
1646.2
1643.4
1640.5
1637.7
27132.7
30906.3
34688.3
38481.5
42288.4
46111.2
-212834.9
-212775.2
-212707.9
-212640.1
-212574.1
-212506.4
24
25
26
27
28
29
1634.9
1632
1629.1
1626.3
1623.4
1620.5
49952
53816.7
57699.9
61611.9
65552.7
69525.8
-212436.1
-212381.4
-212300.6
-212232.9
-212165.3
-212099.4
30
31
1617.5
1614.6
73532
77573.8
-212028.4
-211951.4
Table 5. Point coordinates calibrated by et and e 2
In Figure.5, the true values (point coordinates measured by total
station) were represented by data set 1; the raw data (point
coordinates calculated without considering ei and e 2 ) were
represented by data set 2; the calibrated data (point coordinates
calculated considering ei and e 2 ) were represented by data set 3 .
Figure 5 . The errors caused by change of beam divergence
angle before and after calibration
4. DISCUSSION
accuracy of AOE-LiDAR is required to be O.lmRad; that means
at the distance of 200m, the errors on X axis and Y axis were
less than 20mm. Before calibration, the residuals were dx =
±21.5mm, dy = ±35.5mm, dz = ±5.2mm. After calibration, the
residuals reduced to dx = ±1.2mm, dy =± 0.8mm, dz = ±1.6mm.
That satisfied the pointing accuracy of AOE-LiDAR.
In future research, an improved calibration method will be
studied, which contained the error factors in a general
mathematic model. The relativity between the error factors is
complex; the general mathematic model would help to increase
the LiDAR data precision.
5. CONCLUSIONS
When tuning the beam divergence angle (which changed the
footprint size), the movement of mechanical parts made the
optical axis shift and the laser pointing direction shift at the
same time. In other words, switching laser beam divergence
angle made the laser pointing accuracy degraded. From
formulae (1) ~ (9), the optical axis shifting errors were
calculated in the ground experiment. After calibration the
system error caused by vector E was removed, the pointing
precision of AOE-LiDAR increased obviously, which was
increased from ±0.2mRad to ±0.01mRad.
REFERENCES
Baltsavias, E.P., 1999a. A comparison between
photogrammetry and laser scanning. ISPRS Journal of
Photogrammetry and Remote Sensing, 54, 83-94.
Baltsavias, E.P., 1999b. Airborne laser scanning: basic relations
and formulas. ISPRS Journal of Photogrammetry and Remote
Sensing, 54, 199-214.
Burman, H., 2000. Calibration and Orientation of Airborne
Image and Laser Scanner Data Using GPS and INS, PhD
dissertation, Photogrammetry Reports No. 69, Royal Institute of
Technology, Stockholm, 107p.
Luis Gon^alves-Seco, David Miranda, Rafael Crecente and
Javier Farto. Digital Terrain Model generation using airborne
LiDAR in a forested area of Galicia, Spain. 7th International
Symposium on Spatial Accuracy Assessment in Natural
Resource andEnviromental Sciences, 169-180.
Nora Csanyi May, Charles K. Toth, 2007. Point Position
Accuracy of Airborne LiDAR Systems: A Rigorous Analysis.
International Archives of Photogrammetry, Remote Sensing and
Spatial Information Sciences, 36, 107-111.
Wehr, A., Lohr, U., 1999. Airborne laser scanning - an
introduction and overview. ISPRS Journal of Photogrammetry
and Remote Sensing, 54, 68-82.
From the data above, obvious system errors were found when
tuning the beam divergence of LiDAR; actually the errors were
caused by the shift of the optical axis. It was hard to make the
incidence point on the mirror immobile when tuning beam
divergence. From the experiment, shift of the incidence point
was calculated, error vector E was added to formula (6), the
errors of recalculated scan points were reduced. The pointing
ACKNOWLEDGEMENTS
The authors would like to thank the LiDAR Department,
Academy of Opto-Electronics, Chinese Academy of Sciences
for having supported LiDAR data acquisition.