The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
Figure 9. Residual distribution after coregistration between SAT-PP and PCI DSMs in Euclidean direction and in height. 
7 CONCLUSIONS AND PROSPECTS 
A Cartosat-1 stereopair belonging to test field TS- 
Castelgandolfo was processed in order to test image quality, 
orientation with different models and software, effectiveness of 
image filtering for enhancing the DSM generation and potential 
for DSM generation itself. 
The main results can be summarized as: 
• the noise is intensity dependent, with smaller noise values 
at low grey levels 
• the MTF values for along-track direction are always larger 
(and thus better) than those for cross-track direction and the 
BANDA has a remarkable better quality than BANDF 
• the image orientations show sub-pixel accuracies in all 
directions; the rigorous model in PCI software required 
more GCPs than the RPC correction model (based on affine 
transformation) to perform well 
• two different preprocessing strategies were performed: a 
smoothing moving average filter plus the Sobel filter, that 
transformed the images into gradient maps for PCI; Wallis 
filter for SAT-PP; both strategies were found effective for 
the subsequent DSM generation, which led to similar results 
with an overall 3D and vertical accuracy at the level of 2m. 
For future investigations, some of the following points 
could be addressed: 
• additional tests' about the noise level of BANDA vs. 
BANDF have to be performed 
• additional tests using the Leave-One-Out method have to be 
carried out to give general recommendations; moreover, the 
statistical significance of the parameters estimated within a 
rigorous model should be analyzed 
• the dependence of the DSM accuracy on different land 
cover areas has to be analyzed and the overall shift between 
SAT-PP and PCI DSM of about 3 ground pixels in North 
direction, which is the satellite flight direction, has to be 
investigated. 
ACKNOWLEDGEMENTS 
The authors would like to thank Dr. Nandakumar, for the 
establishment and coordination of the ISPRS-ISRO Cartosat-1 
Scientific Assessment Programme (C-SAP), and for accepting 
our Institutes as Investigators. 
Moreover, Compagnia Generale Ripreseaeree S.p.A. (Parma, 
Italy) is acknowledged for supplying the aerial images. 
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