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Table 1 shows the mean height precisions for different sized regions depending on the amount of control points. With an
immense effort, that is control points in every strip, height precision of 1 cm seems to be achievable for 0.01 km? or 1
km” large regions. However, keep in mind that these simulation calculations only refer to the error per strip (offset and
two tilts; parameters a, b and c) and that the possible falsifying influence of vegetation on the terrain heights is not yet
taken into account. Concerning the benefit of additional cross strips, we stated that they, above all, cause a
homogenisation of the final precision of the entire block.
region size con.pt. con.pt. con.pt. con.pt. con.pt. con.pt. con.pte con.pt. con.pt. con.pt. con.pt.
every every 2. every3. every4. every 5. every Very 7. every every every every
strip strip strip strip Strip 6.strip strip ll.strip 13.strp 24. strip 49. strip
25-10000 m2 1 1,6 2 2,5 2.7 3 3,5 4,3 4,5 6,5 9,5
1 km? 1 1 1,5 1,8 23 2,6 2,8 3,4 3,8 5 7
5 km? 0,6 0,6 0,9 1 1,5 1,6 1,9 2,8 3 4 5.5
10 km? 0,5 0,5 0,7 0,8 1,4 1,5 1,5 2,4 25 3,5 4,5
Table 1: Mean height precisions in cm for different numbers of ground control points and different region sizes
5 CONCLUSIONS
In most cases, height strip adjustment allows a significant improvement of the quality of height data. In general, the
height differences of the 50x50 m? areas (tie ‘points’) had 6-10 cm rms-values before, and 3-5 cm rms after strip
adjustment. The decrease of rms is mainly caused by removing systematic strip errors, such as offset and tilts. In some
cases, however, a more sophisticated approach is required. This applies for the occurence of strip deformations, such as
cross strip parabolic deformation, along-track periodic effects and strip torsions.
Apart from the improvement of the precision of the height-data, the strip adjustment including the analysis of along-
track residual profiles and provides the possibility to get a thorough insight in the quality of the delivered laser altimetry
data. The quality of every individual strip can be examined, an important feature for the acceptance procedure
concerning delivered data. In the meantime, the Survey Department has obliged laser data suppliers to perform strip
adjustment to guarantee the quality of delivered data. Considering the various error aspects we found in laserdata,
further reserach has to be done to further analyse the error sources in order to possibly avoid the occurrence of these
errors in the future.
ACKNOWLEDGMENTS
N.A. Kinneging, R. van Heerd, J.G. van der Kraan, J.S. van Noort, RJ. van 't Zand (Meetkundige Dienst,
Rijkswaterstaat), co-authors of the report 'Strookvereffening van laserdata'.
Arnhemse Fijnhouthandel for the photograph.
REFERENCES
Boon, F., 1999, AHN strategie aanpassing. Internal report of Dutch Survey Department (in dutch).
Fritsch, D. and Kilian, J., 1994. Filtering and calibration of laser scanner measurements. Int. Arch. Potogramm. Remote
Sensing 30 (3/1), 227-234.
Huising, E.J. and Gomes Pereira, L.M., 1998. Errors and accuracy estimates of laser data acquired by various laser
scannning systems for topographic applications. ISPRS Journal of Photogrammetry & Remote Sensing 53 (1998) 245-
261
Kilian, J., Haala, N., Englich, M., 1996. Capture and evaluation of airborne laser scanner data. Int. Arch. Photogramm.
Remote Sensing 31 (B3), 383-388.
Min, E.J. de, Kinneging, N.A., Brügelmann, R., Heerd, R.M. van, Kraan, J.G. van der, Noort, J.S. van, Zand, R.J. van 't,
1999, Strip adjustment of laserdata. Internal report of Dutch Survey Department (in dutch).
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 237
