WIÊÈËmÎÈÎÊËÊÊÊÈ 
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
difference between CDED level 1 and SRTM data of Mount 
Carleton is described as follows: Mean error -1.2 ± 15.6 m, 
absolute error 12.1 m, RMSE 15.6 m, Cl 51.2 m, LE 30.5 m 
with 95% of the points to present difference with the range [- 
50.0, 47.0 m]. We founded that vertical accuracy is terrain class 
dependent. Accuracy particularly suffers on terrain with slope 
values higher than 15°. High errors of CDED level 1 are not 
typical of sloping regions. Aspect of the terrain influences both 
the magnitude and the sign of errors in the difference between 
CDED level 1 and SRTM data. But statistically, limited to our 
study area, we can only mention the relative concentration of 
errors in the NE and N directions. The obtained results proved 
that the error is relatively geographic dependent in NE, N 
directions and minimized in the other directions. Like other 
DEM, CDED are slope-dependent. Mostly for SRTM model, 
their accuracy vary in function of the specific vegetation type 
(Miliaresis G.C et al. 2005). The role of vegetation was also 
assessed in our study. It is shown that in the geographic area 
studied, vegetation covers uniformly (various species) 36 x 24 
km. Differences are concentrated on broadleaf and there is not a 
correlation between the percentage of dominant species and 
large range difference. The highest RMSE of 12.7 m among 
species is for broadleaf class which is not dominant in the study 
area. Assessment of the impact of the vegetation was made 
using SRTM (CGIAR-CSI SRTM) and ICESat data. Both 
SRTM and ICESat are subject of the influence of the vegetation. 
We observed that SRTM is much closed to ICESat, but the 
RMSE of 12.7 m confirm the accuracy of ICESat data versus 
CDED level 1. The Pearson's correlation between ICESat and 
CDED level 1, the tendency of the ICESat’profiles indicated 
that data investigated in our study is reliable. 
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