The International Archives of the PhotogrammeUy, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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the height variation of the 70cm HiRISE DTM is directly 
comparable with the local surface roughness values from the 
MOLA laser beam broadening. 
3.2 MOLA local surface roughness results 
The topic investigated in such analysis is the direct comparison 
of the numerical local surface roughness with the height 
deviation of the HiRISE DTM. Figure 4 shows that the local 
surface roughness value, corrected for the slope effects, is 
correlated to the real metre level height variation. 
At first, we extracted the most reliable base height map using 
1.5m resolution HiRISE DTMs from median filtered 3D 
intersection points. The new nominal divergence angle values 
were then fitted as shown in Figure 4 to minimise the 
differences between a slope corrected MOLA local roughness 
and the height variation of normalised HiRISE DTMs. These 
values are then used for the slope correction with MOLA, 
HRSC and CTX DTMs. 
(a) HIRISE height variance 
above the best fitted MOLA 
surface height 
(b) MOLA track profiles over 
HiRISE stereo images 
stddev of stereo hirise height value (n 
(c) local roughness extracted from MOLA beam broadening vs. 
standard deviation of normalised HiRISE height points within 
the corresponding MOLA footprint with nominal divergence 
angle=33 p rad which shows the best correlation between two 
Figure 4. HiRise-MOLA inter-comparison and the divergence 
angle fitted with a normalised (slope reduced) 
HiRISE DTM standard deviation of heights 
Figure 5. The corrected RMS local roughness MOLA profiles 
Even after applying slope correction using MOLA CTX and 
HRSC DTMs, the artifacts due to crossing tracks in the pulse 
beam broadening were not completely resolved (Figure 5). 
However, well corrected local surface roughness areas show the 
correlation with the surface geomorphology to a certain extent. 
As shown in Figure 5, local surface roughness in the MOLA 
track overlaid on an ORI image, shows obvious features. 
4. CONCLUSIONS & FUTURE WORK 
We extracted various resolution stereo DTMs from 50m up to 
0.7m. All important geological and geomorphological 
observations including direct extraction of metre scale local 
height variations can be performed with such multi-resolution