International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part Bl. Istanbul 2004
The output values for the bias parameters for exterior
orientation can be seen in table 8.
Table 8: Adjusted bias values of exterior orientation
Test site x bias (m) | y bias (m) | z bias (m) | ¢ bias (°)
Catalonia 0.09 0.02 -0.01 0.0007
South Bavaria -0.16 0.01 -0.01 0.0012
Only negligibly small bias values have been found for x, y, and
z. The bias of the pitch angle ¢ corresponds to a shift on the
ground in the order of one pixel which is in good agreement
with the nearly constant shifts between the orthoimages.
Another main result of the bundle block adjustment with CLIC
is the object space coordinates of all tie points. These can be
checked against the available DEM. Table 9 summarizes the
results of these comparisons. In the Catalonian case the
standard deviation of the height differences is the same as
before whereas the mean difference is much reduced. For the
Bavarian test site the standard deviation of the height
differences of the CLIC points to the high quality reference
DEM is quite small and comparable to the Catalonian case. A
small tilt of the DEM plane from Northwest to Southeast is
found in the CLIC point heights: high quality GCP in Austria
were not available, unfortunately. The comparison with the
ERS-DEM which covers the full area gives a nice mean
difference of 0 m but a high standard deviation because of the
partly low accuracy of the ERS-DEM, in connection with the
tilt mentioned above.
Table 9: Object space heights of tie points after bundle
adjustment with CLIC compared to reference DEM
Test site reference Analysis of terrain height
DEM differences
Nr. of mean stand.
points diff. (m) | dev. (m)
Catalonia ICC-DEM 15029 -1.2 3.5
DEM-01 75 3.6 24
DEM-02 59 6.0 2.0
Bavaria DEM-03 75 12 22
(south) DEM-04 71 -3.9 2.0
DEM-05 198 -3.7 3.9
DEM-06 635 8.4 4.8
ERS-DEM 15912 0.0 10.6
9, CONCLUSION
It could be shown that a stereoscopic evaluation of SPOT-HRS
data, only using ancillary data delivered by the image provider,
leads to an absolute accuracy of terrain heights in the order of 5
to 9 meter (mean height error), with standard deviations of
about 2 to 4 meter for single points and 4 to 7 meter for the
interpolated DEM in comparison to the reference DEM. A
fusion with a DEM from the SRTM mission shows the potential
of merging DEM from optical and radar data. The absolute
accuracy can be improved by this merging or using ground
control to reach a mean height difference in the order of 1 meter
if sufficiently accurate ground control points are available. The
standard deviations are reduced by DEM filtering, which also
leads to a smoother DEM. The relative accuracy of course
depends on terrain steepness and land use classes, since image
matching algorithms depend on these image features.
Orthoimages can be derived to an absolute location accuracy of
1 to 2 pixels (10 to 20 meter) without ground control.
The difficulty in getting sufficiently accurate and well
distributed GCP stresses once more the benefits of highly
accurate exterior orientation measurements.
10. REFERENCES
R. Bamler, M. Eineder, B. Kampes, H. Runge, H., N. Adam.;
“SRTM and beyond: Current situation and new developments
in spaceborne SAR and InSAR”, Proceedings of the ISPRS
Workshop High Resolution Mapping from Space, Hanover,
Oct. 6.-8. 2003, IPI, Universität Hannover, on CD-ROM
A Bouillon, E. ‘Breton, F. De Lussy, R, Gachet “SPOTS
Geometric Image Quality”, IGARSS 2003, Toulouse, 21.-25.
July 2003, IEEE International Geoscience and Remote Sensing
Symposium
J.P. Gleyzes, A. Meygret, C. Fratter, C. Panem, S. Baillarin, C.
Valorge : “SPOTS : System overview and image ground
segment”, IGARSS 2003, Toulouse, 21.-25. July 2003, IEEE
International Geoscience and Remote Sensing Symposium
C. Heipke, W. Kornus, A. Pfannenstein, *The evaluation of
MEOSS airborne 3-line scanner imagery — processing chain and
results", Photogrammetric Engineering and Remote Sensing,
Vol. 62, No. 3, pp. 293-299, 1996
M. Lehner, R.S. Gill, *Semi-automatic derivation of digital
elevation models from stereoscopic 3-line scanner data",
[APRS, Vol. 29, Part B4 Washington, USA pp. 68-75, 1992
W. Linder, “Geo-Informationssyteme”, Springer-Verlag Berlin,
Heidelberg, Germany, ISBN 3-540-65276-0, 1999
Ra. Müller, M. Lehner, Ru. Müller, “Verification of Digital
Elevation Models from MOMS-2P data” Proceedings of the
ISPRS Workshop “High Resolution Mapping from Space
2001”, Hannover, Germany, on CD-ROM, September 2001
Ru. Müller, G. Palubinskas, P. Reinartz, M. Schroeder, V.
Amann, R. Stätter, “From Airborne Digital Raw Data to Image
Maps“ PFG Photogrammetrie, Fernerkundung, Geoinformation,
Germany, 4, 4, (2003), S. 317-326
Ru. Müller, P.. Reinartz, M. Lehner, .M.. Schroeder,
*Comparison of the Accuracy of DEM from SPOT HRS two-
fold Stereo Data and HRS/HRG three-fold Stereo Data in
Barcelona Test Site", Proceedings of the ISPRS xX Congress,
Istanbul 12-23 July 2004
P. Reinartz, M. Lehner, Ru. Miiller,M. Schroeder, “First Results
on Accuracy Analysis for DEM and Orthoimages Derived from
SPOT HRS Stereo Data over Bavaria”, Proceedings of the
ISPRS Workshop High Resolution Mapping from Space,
Hannover, Oct. 6.-8. 2003, IPI, Uni Hannov., on CD
A. Roth, W. Knoepfle, S. Gebhardt, B. Rabus, D. Scales,
“Evaluation of Interferometric Digital Elevation Models
Derived from ERS Tandem Data” ISPRS Commission ll
Symposium, Cambridge, UK, 13.-17.7.1998, ISPRS,
International Archives of Photogrammetry and Remote Sensing,
S. 242-247, (1998)
SPOT IMAGE, “SPOT Satellite Geometry Handbook", S-NT-
73-12-SI, Edition 1, Rev. 0, Toulouse, France 2002
T. Toutin, P. Cheng, “DEM Generation with ASTER Stereo
Data”, Earth Observation Magazine, Vol. 10, No. 6, pp. 10-13,
June 2001
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